Q8. Genetic Diversity and Sexual Reproduction: calculate how many genotypes would be possible among the children of Bob and Anne for the combined DNA profile from the D3S1358, vWA, and FGA.
Human geneticists are often asked why children have not inherited a particular trait from their parents. As a human geneticist, you know that one mechanism to insure genetic diversity is the independent assortment of alleles of different loci during gamete (egg and sperm) production, i.e. Mendel's Second Law of Genetics. To illustrate this important genetic principle, calculate how many genotypes would be possible among the children of Bob and Anne for the combined DNA profile from the D3S1358, vWA, and FGA. If you feel really ambitious, now calculate the possible genotypes of the children of Bob and Anne for all 13 CODIS STR loci.
First, write out the possible genotypes for each loci that the children could have. For example, at the vWA there is only one possibility since both parents are homozygous at that locus. For the other two loci there are >1 possible genotypes. Then use the product rule to determine the number of possible genotype combinations the offspring could have by multiplying the numbers of genotypes at each of the three loci to get a probability of the combined genotype.
Q9. How many genotypes are possible in a population for a three locus DNA Profile?
If there are two alleles, A and B, at a genetic locus in a population, there are three possible genotypes, namely AA, BB, and AB. If there are three alleles, A or B or C, there are six possible genotypes, namely AA, BB, CC, AB, AC, and BC. For N different alleles, the total possible genotypes is given by the following expression:
(n x (n+1))
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2
If we assume that the allele reference ladders from our data collection exercise represent all possible alleles (a conservative estimate), how many genotypes are possible in a population for the combined STR loci of D3S1358, vWA, and FGA? The number of alleles is found in the table on page 1 of this handout. Figure out the possible number of genotypes at each locus, then multiply them together.