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# Analysis of Alleles

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1. If a population consists of 122 individuals, how many alleles are present in the population?
2. In the same population of 122 individuals, 25% have the recessive phenotype.
a. How many individuals have the recessive phenotype?
b. How many alleles are present in individuals with the recessive phenotype?

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1. If a population consists of 122 individuals, how many alleles are present in the population?

There are 20,000-25,000 protein coding genes in the human genome. While each gene may have more than two alleles per gene, each person can only carry a maximum of two different alleles at each gene.

Exactly how many unique alleles are present in a population would depend on the frequency of each allele for each gene.

However, we can calculate the number of allele positions for the 20,000-25,000 protein coding genes in the human genome. Since each person can have a maximum of two allele positions, the total alleles per person is 40,000-50,000. In a a population of 122, that would mean 4,800,000-6,100,000 possible allele positions. Also, remember that the sex chromosomes do not necessarily have corresponding alleles.

The Hardy-Weinberg equilibrium can be used to calculate the frequency of alleles in a population of known size as long as we know how many alleles there are for the given gene and some phenotype data.

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2. In the same population of 122 individuals, 25% have the recessive phenotype.

a. How many individual have the recessive phenotype?
The number of individuals is 30 (122*0.25 = 30.5, round down because you cannot have half a person).
b. How many alleles are present in individuals with the recessive phenotype?
A recessive phenotype is caused by two copies of a recessive allele. That means that there is only one allele (duplicated) at the gene in question.