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The Hardy and Weinberg equilibrium indicates the stability of a population over generations. The frequency of the genotype Z/Z = p*p = p2 , because they originate from a combination of sperm cells and oocytes carrying the Z allele each with a frequency of p. The frequency of the genotype z/z = q*q = q2 , because they originate from a combination of sperm cells and oocytes carrying the z allele each with a frequency of q. The genotype Z/z is created in two ways: by combination of a sperm cell with the Z allele (frequency p) and an oocyte with the z allele (frequency q) and by combination of a sperm cell with the z allele (frequency q) and an oocyte with the Z allele (frequency p). Therefore the frequency of the genotype Z/z = 2*p*q = 2pq.
Table 1: The frequencies of alleles and genotypes when animals are mated in a population in Hardy and Weinberg equilibrium
Oocyte Sperm cell | Allele Z | Frequency p | Allele z | Frequency q |
|---|---|---|---|---|
Allele Z | ZZ |
| Zz | |
Frequency P | P2 | pq | ||
Allele z | Zz | zz | ||
Frequency p | pq | q2 |
AAllele and genotype frequencies in a population determine the proportion of animals with different phenotypes for monogenic traits. The effect of selection for desired monogenic traits or against undesired monogenic traits depends partly of the underlying allele frequencies. That is the reason to pay attention to allele and genotype frequencies here.
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