Large amounts of genetic variability exist in the human population. This is evidenced by the fact that with the exception of identical twins, we all appear different from each other. Hair color, eye color, height, and shape all represent alleles in our genetic makeup. To gain a better appreciation for how the numbers of alleles present at a particular locus impacts the variability, let us consider the ABO blood group. Three alleles are possible: A, B, and O. These three alleles can be combined to form three possible homozygous genotypes (AA, BB, and OO) and three heterozygous genotypes (AO, BO, and AB). Thus, with three alleles there are six possible genotypes. However, with AA and AO appearing the same and BB and BO being phenotypically equivalent, there are only four phenotypically expressed blood types: A, B, AB, and O.
With larger numbers of alleles for a particular DNA marker, a greater number of genotypes result. In general, if there are n alleles, there are n homozygous genotypes and n (n — 1)/2 heterozygous ones. Thus, a locus with ten possible alleles would exhibit 10 homozygous possibilities plus [10X (10 — 1)]/2heterozy-gous possibilities or 10 + 45 = 55 total genotypes. A locus with 20 possible alleles would exhibit 20 + (20 X 19)/2 = 210 genotypes. A combination of 10 loci with 10 alleles in each locus would have over 2.5 X 1017 possible genotypes (55 X 55 X 55 X...). Whereas the use of four loci with 30 alleles in each locus would have 465 genotypes each and 4.7 X 1010 possible genotypes (465 X 465 X 465 X 465). The number of observed alleles per locus and the number of loci per DNA test both help produce a larger number of genetically possible genotypes.
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This book discusses the futility of curing stammering by common means. It traces various attempts at curing stammering in the past and how wasteful these attempt were, until he discovered a simple program to cure it. The book presents the life of Benjamin Nathaniel Bogue and his struggles with the handicap. Bogue devotes a great deal of text to explain the handicap of stammering, its effects on the body and psychology of the sufferer, and its cure.