Relationship Between Number Of Alleles And Number Of Possible Genotypes

Allele frequency refers to the number of copies of an allele in a population divided by the total number of all alleles in this population. Genotype frequency refers to the number of individuals with a particular genotype divided by the total number of individuals. Figure 19.4 graphically depicts the relationships between allele frequencies and genotype frequencies. In terms of the total number of alleles and genotypes, if n alleles exist for a genetic marker, then n(n + 1)/2 genotypes are possible.

Table 19.1 includes the number of theoretically possible genotypes for the 13 Combined DNA Index System (CODIS) core STR loci based on the number of reported alleles that are listed in Appendix I. For example, there have been 20 different CSF1PO alleles reported in the literature. Thus, 20(20 + 1)/2 or 210 genotypes are theoretically possible for CSF1PO based on the alleles reported so far. However, many alleles are rather rare and thus not likely to give rise to a particular genotype containing them. Note that in a U.S. population study of

Figure 19.4

Graph depicting genotype frequencies for AA, Aa, and aa when Hardy—Weinberg equilibrium conditions are met. The highest amount of heterozygotes Aa are observed when alleles frequencies for both A and a are 0.5. Adapted from Hartl and Clark (1997).

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  • mezan
    How to work out number of alleles from genotype and number of individuals?
    1 year ago

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