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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
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