Appendix 2: Racial Mixing in Selected European Groups Part 4: MENDEL'S LAWS OF INHERITANCE; THE SANDRA LAING CASE AND W.E. DU BOIS The German monk, Gregor Mendelev, developed the laws of inheritance which still define our understanding of mixed gene pools. The Mendelian Laws of inheritance are critical to a proper understanding of the composition of racially mixed populations. They determine to what extent certain racial characteristics are visible to the casual observer, and which are dominant and which are recessive. DEFINITIONS A chromosome is the name given to any of the linear or sometimes circular DNA-containing bodies of viruses, bacteria, and the nucleus of higher organisms that contain most or all of the individual's genes. A gene is a hereditary unit that occupies a specific location on a specific chromosome and determines a particular characteristics in an organism. There may be one version or many different versions of each gene; these different versions are called 'allele'. Except for identical twins, all individuals (called ‘phenotypes’) have a unique set of alleles. Populations with distinguishing characteristics such as colors or shapes are called genotypes. DOMINANT AND RECESSIVE ALLELES Mendel discovered genetics when he obtained seeds of pea plants that always produced tall plants and seeds that always produced short plants. He raised the plants and then crossed them by transferring pollen from one plant to another. He found that plants from the resultant seeds (first generation) were all tall, but he allowed them to self-pollinate and produced another generation, three-quarters of which were tall and one-quarter short. THE LAWS OF HEREDITARY From his experiments, Mendel was able to draw the following conclusions:
HOMOZYGOUS AND HETEROZYGOUS CONDITIONS Capital letters are used to schematically represent an allele that determines a dominant character, and a small letter for one that determines a recessive character. When the two genes of the genotype’s pair are of the same type (AA) or (aa), the condition is called homozygous for that character. If the two members of a pair are different (Ab or Ba), the condition is called heterozygous. Mendel’s original tall seeds were (AA) and the short (bb). The first generation plants were all (Ab). The second-generation plants of Mendel's experiment were composed of one-quarter (AA), one-half (Ab) and one-quarter (bb). Since tallness was dominant, both (AA) and (Ab) appeared tall, and the (bb) appeared short, accounting for the ratio of tall to short. As this relates to humans, every somatic (normal body) cell of each individual contains 46 chromosomes, as 23 diploid pairs. The chromosomes are tightly bundled strands of DNA. A gene for any particular character occupies a fixed position on one of these 23 strands. With two sets of these 23 strands, the cell contains, for each gene, one allele in duplicate (homozygous) or two different alleles (heterozygous) for each gene. There can be many alternate forms, or alleles, for each gene. The unique combination of alleles that comprise their diploid chromosomes (called the genotype) defines an individual. DOMINANCE AND RECESSIVE ALLELES Dominant and recessive alleles are always relatively positioned to each other: in other words, for a given gene, allele (A) may be more dominant than allele (B), and (B) more dominant than (C). The same holds for different recessive alleles. In the same genome, one allele will usually prove dominant over the other. The terms dominant and recessive must be viewed as a single continuous scale, as relatively dominant or relatively recessive. RACE MIXING AND THE “THROWBACK” GENE In a practical example, if a pure Black breeds with a pure White, the offspring might emerges with a new "mutant" recessive allele (a), being heterozygous (i.e., along with a more dominant one, represented by "Ab"). If that mixed race individual then marries back into the White genotype pool, statistically, only half that person’s progeny will carry (a), and only half of the next generation. A mutant allele may simply disappear or it may propagate out through many generations before it reappears through mixing with another individual who also carries that same allele. Only then will the phenotype appear – this is known popularly known as the “throwback gene.” It may take many generations before a particular combination of alleles (mutant or otherwise) appears. Such a “throwback” will increase the (aa) population locally, and even more when (aa) males start mating with (aa) females, making it possible for an (aa) type to expand in numbers. A “THROWBACK” TEXT BOOK CASE: SANDRA LAING In South Africa, a large White population has existed since the 1600s, when Europeans first started settling that country. Over the 400 years since, the proximity of so many different races has inevitably led to a degree of interbreeding.
Sandra Laing was born in 1955 in Piet Retief, a conservative small town in what was then Apartheid South Africa. Her Afrikaans-speaking parents were classified White, as were her two brothers, and they all appeared on the face of things, to be White. However, when Sandra was born, her skin was noticeably darker, and became more so as the years passed. Her hair texture and features had become so obviously “colored” or mixed race by the time she went to school that she was forced to leave the White school systems and enter that set aside for non-Whites. The Sandra Laing case remains as one of the most striking examples of recessive alleles finally having recombined after several generations, and once again forming an individual reflective of racial mixing which occurred several generations previously.
W.E. DU BOIS - "BLACK" AMERICAN ACTIVIST W.E. du Bois (1868-1963), was an African American activist who conducted the initial research on the Black experience in the United States. His work paved the way for the civil rights, Pan-African, and Black Power movements in the United States. He coined the phrase "Black Power" and who is still today highly regarded in Black American circles. Yet Du Bois himself , as can be seen from his picture (left) was clearly another example of the Mendelian Laws of Inheritance at work: and was, on the face of it, not "Black" at all. In his particular case, the recessive "White" alleles combined in his parents to produce a particularly White-looking individual. MIXED RACIAL TYPES IN THE MIDDLE EAST
In the Middle East, racial mixing has been occurring for many thousands of years, with the inbreeding amongst already racially mixed types causing the mixed grouping to become the dominant grouping in all of these countries. In Iran, for example, a wide variety of physical types can be seen, as in the picture, right, of three girls on a Teheran street. Note the girl on the left of the picture has blond hair, the girl in the centre has dark skin and hair, while the girl on the right has light skin and dark hair. It is still possible to this day to find Whites in Iraq, Iran, Afghanistan and other neighboring countries - although they are few and far between.
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