On the planet Trogus, the population of Trogites have an autosomal gene, HDZ, with two alleles, T and t. T is dominant to t. Individuals with the T allele in their genotype show a propensity for sorbet, while the remainder prefer ice cream. In multiple population studies, 60% of individuals with the TT genotype prefer sorbet, 25% of Tt individuals prefer sorbet, and 5% of tt individuals prefer sorbet. In an F1 cross of Tt x Tt genotypes, among the F2 population of individuals who prefer ice cream, what is the probability that a random individual has the tt genotype

To answer that question, you need to solve a Punnett Square. The Punnett Square allows you to observe the crossing of two parents, being able to observe the relationship between the alleles of each parent in the construction of the offspring. Punnett Square, is made on a table with eight squares. The alleles of one parent are placed in the first row, while the alleles of the other parent are placed in the first column. Therefore, each allele of one parent is combined with the allele of the other, as the remaining squares are filled. This combination of alleles leads to the genetic probability of a possible offspring.

In the case of the question above, the cross between the alleles of parents that both have the Tt (Tt x Tt) alleles is shown below, using the Punnett square.

T t

T TT Tt

t Tt tt

At this intersection, we can see that the "tt" alleles only appeared once in an offspring of 4 possibilities. Thus, we have a 1/4 calculation that is equal to 0.25, which represents a 25% probability that the offspring of this crossing will present individuals with the "tt" alleles.