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
Compare and contrast the results of the reciprocal crosses in the context of autosomal gene inheritance.

Verified step by step guidance

1. Step 1: Begin by understanding the concept of autosomal gene inheritance. Autosomal genes are located on non-sex chromosomes, meaning they are inherited equally by males and females. Traits controlled by autosomal genes are not influenced by the sex of the parent.
2. Step 2: Analyze the results of Cross 1. In the P₁ generation, a male leopard is crossed with a male mottled. The F₁ generation shows all mottled offspring, indicating that the mottled trait is dominant over the leopard trait. In the F₂ generation, the ratio of mottled to leopard offspring is approximately 3:1, which is consistent with Mendelian inheritance for a single autosomal gene with complete dominance.
3. Step 3: Examine the results of Cross 2. In the P₁ generation, a male mottled is crossed with a female leopard. The F₁ generation again shows all mottled offspring, confirming that the mottled trait is dominant. In the F₂ generation, the ratio of mottled to leopard offspring is again approximately 3:1, consistent with autosomal inheritance.
4. Step 4: Compare the results of the reciprocal crosses. Both crosses yield identical patterns of inheritance, with all F₁ offspring being mottled and the F₂ generation showing a 3:1 ratio of mottled to leopard. This indicates that the inheritance of the trait is autosomal and not influenced by the sex of the parent.
5. Step 5: Conclude that the results of the reciprocal crosses support the hypothesis that the dorsal pigment pattern in frogs is controlled by a single autosomal gene with the mottled trait being dominant over the leopard trait. The identical outcomes in both crosses confirm that the gene is autosomal and not sex-linked.

Key Concepts

Autosomal Inheritance

Autosomal inheritance refers to the transmission of genes located on the autosomes, which are the non-sex chromosomes. Traits controlled by autosomal genes can be dominant or recessive. In this case, the dorsal pigment pattern in frogs is influenced by an autosomal gene, where the mottled phenotype appears to be dominant over the leopard phenotype, as indicated by the F₁ generation showing all mottled offspring.

Reciprocal Crosses

Reciprocal crosses involve mating individuals of different phenotypes to observe the inheritance patterns of traits. In this scenario, two reciprocal crosses were performed between leopard and mottled frogs. The results from both crosses show that the F₁ generation is consistently mottled, suggesting that the trait's dominance is not influenced by the sex of the parent, which is a key aspect of understanding autosomal inheritance.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in the offspring resulting from genetic crosses. In the F₂ generations of both crosses, the observed ratios of mottled to leopard frogs (70:22 and 50:18) suggest a consistent pattern of inheritance. These ratios can be analyzed to infer the underlying genetic mechanisms, such as the dominance of the mottled trait over the leopard trait in this autosomal inheritance scenario.