The dorsal pigment pattern of frogs can be either 'leopard' (white pigment between dark spots) or 'mottled' (pigment between spots appears mottled). The trait is controlled by an autosomal gene. Males and females are selected from pure-breeding populations, and a pair of reciprocal crosses is performed. The cross results are shown below.

        Cross 1:    P₁: Male leopard x male mottled
                          F₁: All mottled
                          F₂: 70 mottled, 22 leopard
        Cross 2:    P₁: Male mottled x female leopard
                          F₁: All mottled
                          F₂: 50 mottled, 18 leopard

In the F₂ progeny from both crosses, what proportion is expected to be homozygous? What proportion is expected to be heterozygous?

Key Concepts

Autosomal Inheritance

Autosomal inheritance refers to the transmission of traits controlled by genes located on the autosomes, which are the non-sex chromosomes. In this case, the dorsal pigment pattern in frogs is determined by an autosomal gene, meaning that both males and females have an equal chance of inheriting the trait. Understanding this concept is crucial for predicting the inheritance patterns observed in the F1 and F2 generations.

Genotypic Ratios

Genotypic ratios describe the relative frequencies of different genotypes in the offspring resulting from a genetic cross. In the given scenario, the F2 generation shows a specific ratio of mottled to leopard frogs, which can be used to infer the underlying genotypes. By applying Mendelian genetics, one can determine the expected proportions of homozygous and heterozygous individuals based on the observed phenotypic ratios.

Homozygosity and Heterozygosity

Homozygosity refers to having two identical alleles for a particular gene, while heterozygosity means having two different alleles. In the context of the frog crosses, understanding the expected proportions of homozygous and heterozygous individuals in the F2 generation is essential for predicting the inheritance of traits. The observed phenotypic ratios can help calculate these proportions, providing insights into the genetic makeup of the offspring.