Download Racial Mixing - An Overview - Mendelan Laws of InheritancePart 4

Racial Mixing - An Overview - Mendelan Laws of InheritancePart 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:
There are hereditary factors (called genes).
In each phenotype, two genes exist for each character.
At the time of sex-cell formation, the genes of a pair separate equally into
the gametes. Geneticists call this the law of segregation.
The gametes bear only one gene for each characteristic.
Genes for different characters sort independently of one another at gamete
formation. Geneticists call this the law of independent assortment.
Gametes join randomly, irrespective of the alleles they carry. This is
extremely important to consider when viewing mixed race offspring, and
accounts for the apparent random appearance of mixed racial types – some might
be very dark, others might be quite light).
The characters that appear in the first generation (in this case, tall plants)
are called dominant and the characters that appear in one-quarter of the
second generation are called recessive. Geneticists call this phenomenon the
law of dominance.
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.
Above: Sandra Laing and her parents. With no immediately obvious sign of
Non-white ancestry, the particular combination of her parent's genes
triggered the Mendelian effect of recombining a Non-white gene string,
long hidden in the family, producing the very obvious mixed racial type.
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 - a famous "Black" American activist who coined the phrase
"Black Power" yet who was hardly Black himself.
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.
Part 1: Racial Mixing in Selected European Groups: IntroductionPart 2: The
Black African Genetic Footprint: Sickle Cell DiseasePart 3: Racial Mixing
Brought the Hemoglobin D disorder to Britain and IrelandPart 4: The
Mendelian Laws of Genetics - dominant and recessive racially mixed genes
Part 5: European Footprint: Hereditary Hemochromatosis - a genetically
inherited diseasePart 6: Genetic Evidence of Avar and Hunnish Admixture in
Central EuropePart 7: Western European Genetic Remnants in EgyptPart 8:
Genetic Evidence of Racial Mixing in Greece
Part 9: Genetic Evidence of Racial Mixing in ItalyPart 10: Genetic
Evidence of Racial Mixing in PortugalPart 11: Genetic Evidence of Racial
Mixing in SpainPart 12: Genetic Homogeneity in Poland
Part 13: Genetic Homogeneity in NorwayPart 14: Finland, the Lapps and the
Tat-C ControversyPart 15: Y-Chromosomes as Racial Markers
White History Main Page