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104-473: With the rise of modern genetics , the concept of distinct human races in a biological sense has become obsolete. In 2019, the American Association of Biological Anthropologists stated: "The belief in 'races' as natural aspects of human biology, and the structures of inequality ( racism ) that emerge from such beliefs, are among the most damaging elements in the human experience both today and in

208-455: A Moravian Augustinian friar working in the 19th century in Brno , was the first to study genetics scientifically. Mendel studied "trait inheritance", patterns in the way traits are handed down from parents to offspring over time. He observed that organisms (pea plants) inherit traits by way of discrete "units of inheritance". This term, still used today, is a somewhat ambiguous definition of what

312-429: A helical structure (i.e., shaped like a corkscrew). Their double-helix model had two strands of DNA with the nucleotides pointing inward, each matching a complementary nucleotide on the other strand to form what look like rungs on a twisted ladder. This structure showed that genetic information exists in the sequence of nucleotides on each strand of DNA. The structure also suggested a simple method for replication : if

416-534: A sexual process for transferring DNA from one cell to another cell (usually of the same species). Transformation requires the action of numerous bacterial gene products , and its primary adaptive function appears to be repair of DNA damages in the recipient cell. The diploid nature of chromosomes allows for genes on different chromosomes to assort independently or be separated from their homologous pair during sexual reproduction wherein haploid gametes are formed. In this way new combinations of genes can occur in

520-540: A "Nordic race". The British-born German racialist Houston Stewart Chamberlain considered the Nordic race to be made up of Celtic and Germanic peoples , as well as some Slavs . Chamberlain called those people Celt-Germanic peoples , and his ideas would influence the ideology of Nordicism and Nazism . Madison Grant , in his 1916 book The Passing of the Great Race , took up Ripley's classification. He described

624-509: A "Nordic" or "Baltic" type: "long skulled, very tall, fair skinned, with blond, brown or red hair and light coloured eyes. The Nordics inhabit the countries around the North and Baltic Seas and include not only the great Scandinavian and Teutonic groups, but also other early peoples who first appear in southern Europe and in Asia as representatives of Aryan language and culture." According to Grant,

728-582: A DNA molecule. In 1983, Kary Banks Mullis developed the polymerase chain reaction , providing a quick way to isolate and amplify a specific section of DNA from a mixture. The efforts of the Human Genome Project , Department of Energy, NIH, and parallel private efforts by Celera Genomics led to the sequencing of the human genome in 2003. At its most fundamental level, inheritance in organisms occurs by passing discrete heritable units, called genes , from parents to offspring. This property

832-630: A Nordic race, used the term 'Aryan' to refer to the tribes of the Iranian plains. In Rassenkunde des deutschen Volkes (Racial Science of the German People), published 1922, Hans F. K. Günther identified five principal European races instead of three, adding the East Baltic race (related to the Alpine race) and Dinaric race (related to the Nordic race) to Ripley's categories. This work

936-493: A complex trait is called heritability . Measurement of the heritability of a trait is relative—in a more variable environment, the environment has a bigger influence on the total variation of the trait. For example, human height is a trait with complex causes. It has a heritability of 89% in the United States. In Nigeria, however, where people experience a more variable access to good nutrition and health care , height has

1040-483: A different parent. Many species have so-called sex chromosomes that determine the sex of each organism. In humans and many other animals, the Y chromosome contains the gene that triggers the development of the specifically male characteristics. In evolution, this chromosome has lost most of its content and also most of its genes, while the X chromosome is similar to the other chromosomes and contains many genes. This being said, Mary Frances Lyon discovered that there

1144-546: A diploid cell with paired chromosomes. Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes. Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs . Although they do not use the haploid/diploid method of sexual reproduction, bacteria have many methods of acquiring new genetic information. Some bacteria can undergo conjugation , transferring

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1248-429: A gene is used to produce a specific amino acid sequence . This process begins with the production of an RNA molecule with a sequence matching the gene's DNA sequence, a process called transcription . This messenger RNA molecule then serves to produce a corresponding amino acid sequence through a process called translation . Each group of three nucleotides in the sequence, called a codon , corresponds either to one of

1352-470: A group with an especially high percentage of blondness, which represent a depigmentated Mediterranean". In her work Races of Man (1963, 2nd Ed. 1965) Sonia Mary Cole went further to argue that the Nordic race belongs to the "brunette Mediterranean" Caucasoid division but that it differs only in its higher percentage of blonde hair and light eyes. The Harvard anthropologist Claude Alvin Villee Jr. also

1456-482: A heritability of only 62%. The molecular basis for genes is deoxyribonucleic acid (DNA). DNA is composed of deoxyribose (sugar molecule), a phosphate group, and a base (amine group). There are four types of bases: adenine (A), cytosine (C), guanine (G), and thymine (T). The phosphates make phosphodiester bonds with the sugars to make long phosphate-sugar backbones. Bases specifically pair together (T&A, C&G) between two backbones and make like rungs on

1560-435: A higher body temperature. In a low-temperature environment, however, the protein's structure is stable and produces dark-hair pigment normally. The protein remains functional in areas of skin that are colder—such as its legs, ears, tail, and face—so the cat has dark hair at its extremities. Environment plays a major role in effects of the human genetic disease phenylketonuria . The mutation that causes phenylketonuria disrupts

1664-506: A ladder. The bases, phosphates, and sugars together make a nucleotide that connects to make long chains of DNA. Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain. These chains coil into a double a-helix structure and wrap around proteins called Histones which provide the structural support. DNA wrapped around these histones are called chromosomes. Viruses sometimes use

1768-505: A living cell or organism may increase or decrease gene transcription. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate (lacking sufficient waterfall or rain). While the average height the two corn stalks could grow to is genetically determined, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment. The word genetics stems from

1872-515: A masculine and confident " chad ", originated in alt-right memes on 4chan's /pol/ imageboard in 2016. The earliest forms of the meme, which echoed obsolete racial anthropology tropes, depicted the character in competition with a "Mediterranean" figure. The meme crossed over into mainstream culture by late 2020. It has been used in a wide variety of contexts, including the expression of leftist politics and support for diversity and inclusion, despite its roots. There has been discourse about whether

1976-399: A mistaken alignment; this makes some regions in genomes more prone to mutating in this way. These errors create large structural changes in DNA sequence— duplications , inversions , deletions of entire regions—or the accidental exchange of whole parts of sequences between different chromosomes, chromosomal translocation . North European hypothesis The North European hypothesis

2080-430: A number of subfields, including molecular genetics , epigenetics , and population genetics . Organisms studied within the broad field span the domains of life ( archaea , bacteria , and eukarya ). Genetic processes work in combination with an organism's environment and experiences to influence development and behavior , often referred to as nature versus nurture . The intracellular or extracellular environment of

2184-456: A phenotype involves studying identical and fraternal twins , or other siblings of multiple births . Identical siblings are genetically the same since they come from the same zygote. Meanwhile, fraternal twins are as genetically different from one another as normal siblings. By comparing how often a certain disorder occurs in a pair of identical twins to how often it occurs in a pair of fraternal twins, scientists can determine whether that disorder

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2288-403: A series of genes can be combined to form a linear linkage map that roughly describes the arrangement of the genes along the chromosome. Genes express their functional effect through the production of proteins, which are molecules responsible for most functions in the cell. Proteins are made up of one or more polypeptide chains, each composed of a sequence of amino acids . The DNA sequence of

2392-457: A single parent. Offspring that are genetically identical to their parents are called clones . Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome ( haploid ) and double copies ( diploid ). Haploid cells fuse and combine genetic material to create

2496-448: A small circular piece of DNA to another bacterium. Bacteria can also take up raw DNA fragments found in the environment and integrate them into their genomes, a phenomenon known as transformation . These processes result in horizontal gene transfer , transmitting fragments of genetic information between organisms that would be otherwise unrelated. Natural bacterial transformation occurs in many bacterial species, and can be regarded as

2600-400: A smooth blend of traits from their parents. Mendel's work provided examples where traits were definitely not blended after hybridization, showing that traits are produced by combinations of distinct genes rather than a continuous blend. Blending of traits in the progeny is now explained by the action of multiple genes with quantitative effects . Another theory that had some support at that time

2704-452: A transition of heredity from its status as myth to that of a scientific discipline, by providing a fundamental theoretical basis for genetics in the twentieth century. Other theories of inheritance preceded Mendel's work. A popular theory during the 19th century, and implied by Charles Darwin 's 1859 On the Origin of Species , was blending inheritance : the idea that individuals inherit

2808-412: A unique three-dimensional structure for that protein, and the three-dimensional structures of proteins are related to their functions. Some are simple structural molecules, like the fibers formed by the protein collagen . Proteins can bind to other proteins and simple molecules, sometimes acting as enzymes by facilitating chemical reactions within the bound molecules (without changing the structure of

2912-400: A variety of hereditary characteristics that replicate and remain active throughout generations. While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid , containing two of each chromosome and thus two copies of every gene. The two alleles for a gene are located on identical loci of the two homologous chromosomes , each allele inherited from

3016-488: Is X-chromosome inactivation during reproduction to avoid passing on twice as many genes to the offspring. Lyon's discovery led to the discovery of X-linked diseases. When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis , is the simplest form of reproduction and is the basis for asexual reproduction. Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from

3120-482: Is caused by genetic or postnatal environmental factors. One famous example involved the study of the Genain quadruplets , who were identical quadruplets all diagnosed with schizophrenia . The genome of a given organism contains thousands of genes, but not all these genes need to be active at any given moment. A gene is expressed when it is being transcribed into mRNA and there exist many cellular methods of controlling

3224-556: Is certainly a depigmented offshoot from the basic long-headed Mediterranean stock. It deserves separate racial classification only because its blond hair (ash or golden), its pure blue or grey eyes". Coon suggested that the Nordic type emerged as a result of a mixture of "the Danubian Mediterranean strain with the later Corded element". Hence his two main Nordic types show Corded and Danubian predominance, respectively . A third "Hallstatt" type Coon took to have emerged in

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3328-657: Is light-eyed, mostly rather light-haired, low-skulled and long-skulled (dolichocephalic), tall and slender, with more or less narrow face and narrow nose, and low frequency of blood type gene q. The Nordid race has several subraces. The most divergent is the Faelish subrace in western Germany and also in the interior of southwestern Norway. The Faelish subrace is broader of face and form. So is the North-Atlantid subrace (the North-Occidental race of Deniker), which

3432-582: Is like the primary type, but has much darker hair. Above all in the oceanic parts of Great Britain the North-Atlantic subrace is also very high in blood type gene r and low in blood type gene p. The major type with distribution particularly in Scandinavia is here termed the Scandid or Scando-Nordid subrace." Some forensic scientists, pathologists and anthropologists up to the 1990s continued to use

3536-438: Is referred to as a gene. Trait inheritance and molecular inheritance mechanisms of genes are still primary principles of genetics in the 21st century, but modern genetics has expanded to study the function and behavior of genes. Gene structure and function, variation, and distribution are studied within the context of the cell , the organism (e.g. dominance ), and within the context of a population. Genetics has given rise to

3640-441: Is responsible for the development of structures within multicellular organisms, these patterns arise from the complex interactions between many cells. Within eukaryotes , there exist structural features of chromatin that influence the transcription of genes, often in the form of modifications to DNA and chromatin that are stably inherited by daughter cells. These features are called " epigenetic " because they exist "on top" of

3744-497: Is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand. Genes are arranged linearly along long chains of DNA base-pair sequences. In bacteria , each cell usually contains a single circular genophore , while eukaryotic organisms (such as plants and animals) have their DNA arranged in multiple linear chromosomes. These DNA strands are often extremely long;

3848-694: Is the same as that which Mendel published. In his third law, he developed the basic principles of mutation (he can be considered a forerunner of Hugo de Vries ). Festetics argued that changes observed in the generation of farm animals, plants, and humans are the result of scientific laws. Festetics empirically deduced that organisms inherit their characteristics, not acquire them. He recognized recessive traits and inherent variation by postulating that traits of past generations could reappear later, and organisms could produce progeny with different attributes. These observations represent an important prelude to Mendel's theory of particulate inheritance insofar as it features

3952-651: The Alpine race , Dinaric race , Iranid race , East Baltic race , and the Mediterranean race . American economist William Z. Ripley purported to define a " Teutonic race " in his book The Races of Europe (1899). He divided Europeans into three main subcategories: Teutonic, Alpine and Mediterranean . According to Ripley the Teutonic race resided in Scandinavia , northern France , northern Germany ,

4056-459: The Baltic states and East Prussia , northern Poland , northwest Russia , Great Britain , Ireland , and parts of Central and Eastern Europe , and was typified by light hair, light skin, light eyes, tall stature, a narrow nose, and slender body type. It was Ripley who popularized this idea of three biological European races. Ripley borrowed Deniker's terminology of Nordic (he had previously used

4160-486: The Blue-eyed Mary ( Omphalodes verna ), for example, there exists a gene with alleles that determine the color of flowers: blue or magenta. Another gene, however, controls whether the flowers have color at all or are white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles. This interaction between genes is called epistasis , with

4264-580: The Hamburg culture and the Federmesser culture . In these areas of the north are common boreal phenomena apparently described in some Indo-European myths. These groups of hunters and fishermen are the basis of the next Maglemosian culture (9000–6500 BC approximately). The rising of the sea level in northern Europe caused the flooding of part of the territories occupied by Maglemosians ( Doggerland ) and drove them south. The heirs of this culture developed

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4368-517: The Middle East , and North Africa . Only in the 1920s did a strong partiality for "Nordic" begin to reveal itself, and for a while the term was used almost interchangeably with Aryan. Later, however, Nordic would not be co-terminous with Aryan, Indo-European or Germanic. For example, the later Nazi minister for Food, Richard Walther Darré , who had developed a concept of the German peasantry as

4472-748: The Rape of the Sabines in Rome and the war between the Æsir and Vanir of Norse mythology , which would show the union between warrior groups and groups of producers/farmers. Later cultures, such as the Globular Amphora culture and the Corded Ware culture , would represent the expansion of the Indo-Europeans (or Indogermanen according to this hypothesis) from their original locations in

4576-413: The ancient Greek γενετικός genetikos meaning "genitive"/"generative", which in turn derives from γένεσις genesis meaning "origin". The observation that living things inherit traits from their parents has been used since prehistoric times to improve crop plants and animals through selective breeding . The modern science of genetics, seeking to understand this process, began with

4680-415: The neutral theory of molecular evolution through publishing the nearly neutral theory of molecular evolution . In this theory, Ohta stressed the importance of natural selection and the environment to the rate at which genetic evolution occurs. One important development was chain-termination DNA sequencing in 1977 by Frederick Sanger . This technology allows scientists to read the nucleotide sequence of

4784-578: The "Alpine race", shorter in stature, darker in colouring, with a rounder head, predominated in Central and Eastern Europe through to Turkey and the Eurasian steppes of Central Asia and Southern Russia . The "Mediterranean race", with dark hair and eyes, aquiline nose , swarthy complexion , moderate-to-short stature, and moderate or long skull was said to be prevalent in Southern Europe ,

4888-548: The "caucasoid branch of humanity" to three distinct groups. By 1902 the German archaeologist Gustaf Kossinna identified the original Aryans ( Proto-Indo-Europeans ) with the north German Corded Ware culture , an argument that gained in currency over the following two decades. He placed the Indo-European Urheimat in Schleswig-Holstein , arguing that they had expanded across Europe from there. By

4992-515: The 1885 Anthropology Congress in Karlsruhe , Virchow denounced the "Nordic mysticism", while Josef Kollmann, a collaborator of Virchow, stated that the people of Europe, be they German , Italian , English or French , belonged to a "mixture of various races", furthermore declaring that the "results of craniology" led to "struggle against any theory concerning the superiority of this or that European race". Other supposed "Caucasian sub-races" were

5096-421: The DNA sequence and retain inheritance from one cell generation to the next. Because of epigenetic features, different cell types grown within the same medium can retain very different properties. Although epigenetic features are generally dynamic over the course of development, some, like the phenomenon of paramutation , have multigenerational inheritance and exist as rare exceptions to the general rule of DNA as

5200-652: The European Iron Age, in Central Europe, where he said that it was subsequently mostly replaced, but "found a refuge in Sweden and in the eastern valleys of southern Norway." Coon's theories on race were widely disputed in his lifetime, and are considered pseudoscientific in modern anthropology. The depigmentation theory received notable support from later anthropologists, thus in 1947 Melville Jacobs noted: "To many physical anthropologists Nordic means

5304-632: The F1 offspring mate with each other, the offspring are called the "F2" (second filial) generation. One of the common diagrams used to predict the result of cross-breeding is the Punnett square . When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits. These charts map the inheritance of a trait in a family tree. Organisms have thousands of genes, and in sexually reproducing organisms these genes generally assort independently of each other. This means that

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5408-504: The Greek word genesis —γένεσις, "origin", predates the noun and was first used in a biological sense in 1860. Bateson both acted as a mentor and was aided significantly by the work of other scientists from Newnham College at Cambridge, specifically the work of Becky Saunders , Nora Darwin Barlow , and Muriel Wheldale Onslow . Bateson popularized the usage of the word genetics to describe

5512-486: The Nordic: Northwestern , Sub-Nordic , Vistula and Sub-Adriatic , respectively. The notion of a distinct northern European race was also rejected by several anthropologists on craniometric grounds. German anthropologist Rudolf Virchow attacked the claim following a study of craniometry, which gave surprising results according to contemporary scientific racist theories on the " Aryan race ". During

5616-448: The ability of the body to break down the amino acid phenylalanine , causing a toxic build-up of an intermediate molecule that, in turn, causes severe symptoms of progressive intellectual disability and seizures. However, if someone with the phenylketonuria mutation follows a strict diet that avoids this amino acid, they remain normal and healthy. A common method for determining how genes and environment ("nature and nurture") contribute to

5720-444: The adaptive function of repair of DNA damages. The first cytological demonstration of crossing over was performed by Harriet Creighton and Barbara McClintock in 1931. Their research and experiments on corn provided cytological evidence for the genetic theory that linked genes on paired chromosomes do in fact exchange places from one homolog to the other. The probability of chromosomal crossover occurring between two given points on

5824-440: The basis for inheritance. During the process of DNA replication, errors occasionally occur in the polymerization of the second strand. These errors, called mutations, can affect the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. Error rates are usually very low—1 error in every 10–100 million bases—due to the "proofreading" ability of DNA polymerases . Processes that increase

5928-404: The cat plays the role of the environment. The cat's genes code for dark hair, thus the hair-producing cells in the cat make cellular proteins resulting in dark hair. But these dark hair-producing proteins are sensitive to temperature (i.e. have a mutation causing temperature-sensitivity) and denature in higher-temperature environments, failing to produce dark-hair pigment in areas where the cat has

6032-429: The cell, these genes for tryptophan synthesis are no longer needed. The presence of tryptophan directly affects the activity of the genes—tryptophan molecules bind to the tryptophan repressor (a transcription factor), changing the repressor's structure such that the repressor binds to the genes. The tryptophan repressor blocks the transcription and expression of the genes, thereby creating negative feedback regulation of

6136-421: The chromosome is related to the distance between the points. For an arbitrarily long distance, the probability of crossover is high enough that the inheritance of the genes is effectively uncorrelated. For genes that are closer together, however, the lower probability of crossover means that the genes demonstrate genetic linkage; alleles for the two genes tend to be inherited together. The amounts of linkage between

6240-422: The combined DNA sequences of all chromosomes) is called the genome . DNA is most often found in the nucleus of cells, but Ruth Sager helped in the discovery of nonchromosomal genes found outside of the nucleus. In plants, these are often found in the chloroplasts and in other organisms, in the mitochondria. These nonchromosomal genes can still be passed on by either partner in sexual reproduction and they control

6344-520: The cultures of Ertebølle and Ellerbek. Boettcher compares their activities with those of the Vikings of the following millenniums. They are described as a developing warrior society, which deals with trade and piracy, going up the rivers to raid the lands occupied by the Danubian farmers of the southern plains, subduing them and become their leaders. The fusion of these two populations gave rise to

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6448-585: The early 20th century this theory was well-established, though far from universally accepted. Sociologists were soon using the concept of a "blond race" to model the migrations of the supposedly more entrepreneurial and innovative components of European populations. By the early 20th century, Ripley's tripartite Nordic/Alpine/Mediterranean model was well established. Most 19th century race-theorists like Arthur de Gobineau , Otto Ammon , Georges Vacher de Lapouge and Houston Stewart Chamberlain preferred to speak of "Aryans", "Teutons", and "Indo-Europeans" instead of

6552-417: The expression of genes such that proteins are produced only when needed by the cell. Transcription factors are regulatory proteins that bind to DNA, either promoting or inhibiting the transcription of a gene. Within the genome of Escherichia coli bacteria, for example, there exists a series of genes necessary for the synthesis of the amino acid tryptophan . However, when tryptophan is already available to

6656-596: The horse, the wagon and the battle axe , fortifications and signs of a hierarchically organized society". The first Indo-European culture would be then a synthesis of the Ertebølle culture and the final stages of the Linear Pottery culture . This prehistoric fusion of two different populations would explain some common myths to the Indo-European mythology that were studied by Georges Dumézil , such as

6760-469: The information an organism uses to function, the environment plays an important role in determining the ultimate phenotypes an organism displays. The phrase " nature and nurture " refers to this complementary relationship. The phenotype of an organism depends on the interaction of genes and the environment. An interesting example is the coat coloration of the Siamese cat . In this case, the body temperature of

6864-406: The inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers. This phenomenon, known as " Mendel's second law " or the "law of independent assortment," means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. Different genes often interact to influence the same trait. In

6968-427: The largest human chromosome, for example, is about 247 million base pairs in length. The DNA of a chromosome is associated with structural proteins that organize, compact, and control access to the DNA, forming a material called chromatin ; in eukaryotes, chromatin is usually composed of nucleosomes , segments of DNA wound around cores of histone proteins. The full set of hereditary material in an organism (usually

7072-571: The nature of inheritance in plants. In his paper " Versuche über Pflanzenhybriden " (" Experiments on Plant Hybridization "), presented in 1865 to the Naturforschender Verein (Society for Research in Nature) in Brno , Mendel traced the inheritance patterns of certain traits in pea plants and described them mathematically. Although this pattern of inheritance could only be observed for a few traits, Mendel's work suggested that heredity

7176-500: The offspring of a mating pair. Genes on the same chromosome would theoretically never recombine. However, they do, via the cellular process of chromosomal crossover . During crossover, chromosomes exchange stretches of DNA, effectively shuffling the gene alleles between the chromosomes. This process of chromosomal crossover generally occurs during meiosis , a series of cell divisions that creates haploid cells. Meiotic recombination , particularly in microbial eukaryotes , appears to serve

7280-435: The original sequence. A particularly important source of DNA damages appears to be reactive oxygen species produced by cellular aerobic respiration , and these can lead to mutations. In organisms that use chromosomal crossover to exchange DNA and recombine genes, errors in alignment during meiosis can also cause mutations. Errors in crossover are especially likely when similar sequences cause partner chromosomes to adopt

7384-465: The past." The Russian-born French anthropologist Joseph Deniker initially proposed " nordique " (meaning 'northern') as an "ethnic group" (a term that he coined). He defined nordique by a set of physical characteristics: the concurrence of somewhat wavy hair, light eyes, reddish skin, tall stature and a dolichocephalic skull. Of six 'Caucasian' groups Deniker accommodated four into secondary ethnic groups, all of which he considered intermediate to

7488-470: The phenotype of the organism, while the other allele is called recessive as its qualities recede and are not observed. Some alleles do not have complete dominance and instead have incomplete dominance by expressing an intermediate phenotype, or codominance by expressing both alleles at once. When a pair of organisms reproduce sexually , their offspring randomly inherit one of the two alleles from each parent. These observations of discrete inheritance and

7592-457: The present northwestern European center of Nordic concentration" that he determined to be morphologically Nordic, were called "Exotic Nordics". Coon took the Nordics to be a partially depigmented branch of the greater Mediterranean racial stock. This theory was also supported by Coon's mentor Earnest Albert Hooton , who in the same year published Twilight of Man , which stated: "The Nordic race

7696-543: The process of protein production . It was discovered that the cell uses DNA as a template to create matching messenger RNA , molecules with nucleotides very similar to DNA. The nucleotide sequence of a messenger RNA is used to create an amino acid sequence in protein; this translation between nucleotide sequences and amino acid sequences is known as the genetic code . With the newfound molecular understanding of inheritance came an explosion of research. A notable theory arose from Tomoko Ohta in 1973 with her amendment to

7800-435: The product rule, the sum rule, and more. Geneticists use diagrams and symbols to describe inheritance. A gene is represented by one or a few letters. Often a "+" symbol is used to mark the usual, non-mutant allele for a gene. In fertilization and breeding experiments (and especially when discussing Mendel's laws) the parents are referred to as the "P" generation and the offspring as the "F1" (first filial) generation. When

7904-519: The properties of a protein by destabilizing the structure or changing the surface of the protein in a way that changes its interaction with other proteins and molecules. For example, sickle-cell anemia is a human genetic disease that results from a single base difference within the coding region for the β-globin section of hemoglobin, causing a single amino acid change that changes hemoglobin's physical properties. Sickle-cell versions of hemoglobin stick to themselves, stacking to form fibers that distort

8008-426: The protein itself). Protein structure is dynamic; the protein hemoglobin bends into slightly different forms as it facilitates the capture, transport, and release of oxygen molecules within mammalian blood. A single nucleotide difference within DNA can cause a change in the amino acid sequence of a protein. Because protein structures are the result of their amino acid sequences, some changes can dramatically change

8112-406: The rate of changes in DNA are called mutagenic : mutagenic chemicals promote errors in DNA replication, often by interfering with the structure of base-pairing, while UV radiation induces mutations by causing damage to the DNA structure. Chemical damage to DNA occurs naturally as well and cells use DNA repair mechanisms to repair mismatches and breaks. The repair does not, however, always restore

8216-621: The reconstructed Proto-Indo-European vocabulary would restrict the homeland (Urheimat) in a culture of the late Neolithic or the Chalcolithic . Terms in favor of a northern location would be, among others, the ones to indicate the beech ( bhāghos ) and the sea (* mori ). Another issue was the Salmon problem . Others, such as Kossinna, identified specifically the Chalcolithic Corded Ware culture (c. 2900–2300 BC, but at

8320-408: The same allele of a given gene are called homozygous at that gene locus , while organisms with two different alleles of a given gene are called heterozygous . The set of alleles for a given organism is called its genotype , while the observable traits of the organism are called its phenotype . When organisms are heterozygous at a gene, often one allele is called dominant as its qualities dominate

8424-401: The second gene epistatic to the first. Many traits are not discrete features (e.g. purple or white flowers) but are instead continuous features (e.g. human height and skin color ). These complex traits are products of many genes. The influence of these genes is mediated, to varying degrees, by the environment an organism has experienced. The degree to which an organism's genes contribute to

8528-509: The segregation of alleles are collectively known as Mendel's first law or the Law of Segregation. However, the probability of getting one gene over the other can change due to dominant, recessive, homozygous, or heterozygous genes. For example, Mendel found that if you cross heterozygous organisms your odds of getting the dominant trait is 3:1. Real geneticist study and calculate probabilities by using theoretical probabilities, empirical probabilities,

8632-653: The shape of red blood cells carrying the protein. These sickle-shaped cells no longer flow smoothly through blood vessels , having a tendency to clog or degrade, causing the medical problems associated with this disease. Some DNA sequences are transcribed into RNA but are not translated into protein products—such RNA molecules are called non-coding RNA . In some cases, these products fold into structures which are involved in critical cell functions (e.g. ribosomal RNA and transfer RNA ). RNA can also have regulatory effects through hybridization interactions with other RNA molecules (such as microRNA ). Although genes contain all

8736-446: The similar molecule RNA instead of DNA as their genetic material. DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix . Each nucleotide in DNA preferentially pairs with its partner nucleotide on the opposite strand: A pairs with T, and C pairs with G. Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand. This structure of DNA

8840-500: The single celled alga Acetabularia . The Hershey–Chase experiment in 1952 confirmed that DNA (rather than protein) is the genetic material of the viruses that infect bacteria, providing further evidence that DNA is the molecule responsible for inheritance. James Watson and Francis Crick determined the structure of DNA in 1953, using the X-ray crystallography work of Rosalind Franklin and Maurice Wilkins that indicated DNA has

8944-533: The so-called Funnelbeaker culture (4200–2600 BC), extended from the Netherlands to north-western Ukraine , which would be the original habitat of the first Indo-Europeans. For Jean Haudry , "The Neolithic Funnelbecker culture agrees well with the traditional image of the Indo-European peoples confirmed by linguistic paleontology: in this culture there are simultaneously breeding and plant cultivation,

9048-441: The strands are separated, new partner strands can be reconstructed for each based on the sequence of the old strand. This property is what gives DNA its semi-conservative nature where one strand of new DNA is from an original parent strand. Although the structure of DNA showed how inheritance works, it was still not known how DNA influences the behavior of cells. In the following years, scientists tried to understand how DNA controls

9152-580: The study of inheritance in his inaugural address to the Third International Conference on Plant Hybridization in London in 1906. After the rediscovery of Mendel's work, scientists tried to determine which molecules in the cell were responsible for inheritance. In 1900, Nettie Stevens began studying the mealworm. Over the next 11 years, she discovered that females only had the X chromosome and males had both X and Y chromosomes. She

9256-529: The term " Teuton "); his division of the European races relied on a variety of anthropometric measurements, but focused especially on their cephalic index and stature . Compared to Deniker, Ripley advocated a simplified racial view and proposed the concept of a single Teutonic race linked to geographic areas where Nordic-like characteristics predominate, and contrasted these areas to the boundaries of two other types, Alpine and Mediterranean , thus reducing

9360-603: The time known as Battle-Axe culture or, in German, Streitaxtkultur , and dated to c. 2000 BC) with the Proto-Indo-Europeans. For Boettcher, the very first period of formation of the future proto-Indo-European peoples began in the late Paleolithic, when global warming, which followed the Würm glaciation , allowed to the hunter-gatherers settled in the glacial shelters to repopulate northern Europe, now free of ice. They gave rise to archaeological manifestations such as

9464-488: The tripartite division of Caucasoids: Nordic, Alpine and Mediterranean, based on their cranial anthropometry . The anthropologist Wilton M. Krogman for example identified Nordic racial crania in his work "The Human Skeleton in Forensic Medicine" (1986) as being "dolichochranic". A popular internet meme most often referred to as the "Yes Chad" or "Nordic Gamer", which depicts an idealized Nordic-looking man as

9568-536: The tryptophan synthesis process. Differences in gene expression are especially clear within multicellular organisms , where cells all contain the same genome but have very different structures and behaviors due to the expression of different sets of genes. All the cells in a multicellular organism derive from a single cell, differentiating into variant cell types in response to external and intercellular signals and gradually establishing different patterns of gene expression to create different behaviors. As no single gene

9672-482: The twenty possible amino acids in a protein or an instruction to end the amino acid sequence ; this correspondence is called the genetic code . The flow of information is unidirectional: information is transferred from nucleotide sequences into the amino acid sequence of proteins, but it never transfers from protein back into the sequence of DNA—a phenomenon Francis Crick called the central dogma of molecular biology . The specific sequence of amino acids results in

9776-545: The two is responsible for inheritance. In 1928 , Frederick Griffith discovered the phenomenon of transformation : dead bacteria could transfer genetic material to "transform" other still-living bacteria. Sixteen years later, in 1944, the Avery–MacLeod–McCarty experiment identified DNA as the molecule responsible for transformation. The role of the nucleus as the repository of genetic information in eukaryotes had been established by Hämmerling in 1943 in his work on

9880-485: The usage of the character serves as tacit normalization of racist symbols, similar to controversies about other internet memes like Pepe the Frog and wojaks . Genetics This is an accepted version of this page Genetics is the study of genes , genetic variation , and heredity in organisms . It is an important branch in biology because heredity is vital to organisms' evolution . Gregor Mendel ,

9984-538: The work of the Augustinian friar Gregor Mendel in the mid-19th century. Prior to Mendel, Imre Festetics , a Hungarian noble, who lived in Kőszeg before Mendel, was the first who used the word "genetic" in hereditarian context, and is considered the first geneticist. He described several rules of biological inheritance in his work The genetic laws of nature (Die genetischen Gesetze der Natur, 1819). His second law

10088-524: Was a linguistic and archaeological theory that tried to explain the spread of the Indo-European languages in Europe and parts of Asia by locating the original homeland ( Urheimat ) in southern Scandinavia or in the North German Plain . This hypothesis, advanced by Karl Penka , Hermann Hirt , Gustaf Kossinna and others, had some success in the late 19th century and the early 20th century, and

10192-481: Was a notable proponent of this theory, writing: "The Nordic division, a partially depigmised branch of the Mediterranean group." Collier's Encyclopedia as late as 1984 contains an entry for this theory, citing anthropological support. The Swedish anthropologist Bertil Lundman introduced the term "Nordid" to describe the Nordic race in his book The Races and Peoples of Europe (1977) as: "The Nordid race

10296-518: Was able to conclude that sex is a chromosomal factor and is determined by the male. In 1911, Thomas Hunt Morgan argued that genes are on chromosomes , based on observations of a sex-linked white eye mutation in fruit flies . In 1913, his student Alfred Sturtevant used the phenomenon of genetic linkage to show that genes are arranged linearly on the chromosome. Although genes were known to exist on chromosomes, chromosomes are composed of both protein and DNA, and scientists did not know which of

10400-514: Was endorsed by Nazism , but is today considered outdated by the majority of the academics, who tend to favor the Kurgan hypothesis . According to Penka, the first to propose a Nordic Urheimat, the primitive Indo-European people had to be sedentary farmers native of the north, formed without external interference since the Paleolithic . The presence of a term to indicate copper (* ayes ) in

10504-591: Was first observed by Gregor Mendel, who studied the segregation of heritable traits in pea plants, showing for example that flowers on a single plant were either purple or white—but never an intermediate between the two colors. The discrete versions of the same gene controlling the inherited appearance (phenotypes) are called alleles . In the case of the pea, which is a diploid species, each individual plant has two copies of each gene, one copy inherited from each parent. Many species, including humans, have this pattern of inheritance. Diploid organisms with two copies of

10608-559: Was influential in Ewald Banse 's publication of Die Rassenkarte von Europa in 1925 which combined research by Deniker, Ripley, Grant, Otto Hauser , Günther, Eugen Fischer and Gustav Kraitschek . Carleton S. Coon in his book of 1939 The Races of Europe subdivided the Nordic race into three main types, "Corded", "Danubian" and "Hallstatt", besides a "Neo-Danubian" type and a variety of Nordic types altered by Upper Palaeolithic or Alpine admixture. Types found in "places distant from

10712-421: Was particulate, not acquired, and that the inheritance patterns of many traits could be explained through simple rules and ratios. The importance of Mendel's work did not gain wide understanding until 1900, after his death, when Hugo de Vries and other scientists rediscovered his research. William Bateson , a proponent of Mendel's work, coined the word genetics in 1905. The adjective genetic , derived from

10816-529: Was the inheritance of acquired characteristics : the belief that individuals inherit traits strengthened by their parents. This theory (commonly associated with Jean-Baptiste Lamarck ) is now known to be wrong—the experiences of individuals do not affect the genes they pass to their children. Other theories included Darwin's pangenesis (which had both acquired and inherited aspects) and Francis Galton 's reformulation of pangenesis as both particulate and inherited. Modern genetics started with Mendel's studies of

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