Figure E.1 illustrates the results of an electrophoretic analysis of 13 CODIS STR markers on a DNA sample and identifies the alleles for each gene. Table E.2 lists the frequencies for alleles of three of the STRs shown in the figure. Use this information to calculate the frequency of the genotype for STR genes FGA, vWA, and D3S1358 given in Figure E.1.

Verified step by step guidance

1. Identify the alleles for each STR gene (FGA, vWA, and D3S1358) from the electrophoretic analysis results shown in Figure E.1. Note whether the genotype is homozygous (same alleles) or heterozygous (different alleles) for each STR.
2. Locate the allele frequencies for each identified allele of the three STR genes in Table E.2. These frequencies represent the proportion of each allele in the population.
3. For each STR gene, calculate the genotype frequency using the Hardy-Weinberg principle: if the genotype is homozygous (allele A and allele A), use the formula $p^2$, where $p$ is the frequency of allele A; if heterozygous (allele A and allele B), use the formula $2$q, where $p$ and $q$ are the frequencies of alleles A and B respectively.
4. Calculate the genotype frequency for each of the three STR genes separately by substituting the allele frequencies into the appropriate formula from step 3.
5. Multiply the genotype frequencies of the three STR genes together to find the combined genotype frequency for the individual, assuming the loci are independent and in Hardy-Weinberg equilibrium.

Key Concepts

Short Tandem Repeats (STRs)

STRs are short sequences of DNA, typically 2-6 base pairs long, repeated multiple times in a row at specific loci. They are highly polymorphic, making them useful for genetic identification and forensic analysis. Each individual has two alleles per STR locus, inherited from each parent.

Allele Frequency and Genotype Frequency

Allele frequency is the proportion of a specific allele variant in a population. Genotype frequency refers to how often a particular combination of alleles (genotype) occurs. For STRs, genotype frequency can be calculated using allele frequencies, assuming Hardy-Weinberg equilibrium.

Hardy-Weinberg Equilibrium

This principle states that allele and genotype frequencies in a large, randomly mating population remain constant across generations if no evolutionary forces act. It allows calculation of genotype frequencies from allele frequencies using the formula p² + 2pq + q² = 1, where p and q are allele frequencies.