Question

You want to identify dominant /recessive relationship for skin color for a new frog species that you found in the rain forest. Assume that one autosomal gene controls skin color in this species. All of the frogs that you found for that spe- cies are bright blue or yellow. A bright blue female and bright blue male frog mate and produce all bright blue progeny. A yellow female and yellow male frog mate and produce a mix of bright blue and yellow progeny. Identify each trait (bright blue skin color and yellow skin color) as dominant or recessive. Explain your choices.
Required:
Identify the genotype for each parent in the two crosses.

Answer 1

Answer:

bright blue trait = recessive

yellow trait = dominant

Explanation:

let the letter B represent the gene for skin colour.

This means that the dominant gene is 'B' while the recessive gene is 'b'

A dominant gene is one that is exhibited phenotypically in the presence of both gene variants (heter0zygous state - Bb) while a recessive gene is only expressed phenotypically when it is in a h0m0zygous state (bb)

In order to find out the genotype of the parents, let us consider each cross one after the other.

1. A bright blue female and a bright blue male produce all blue progeny.

2. A yellow female and a yellow male produce a mix of both bright blue and yellow progeny

From statement 2, it can be deduced that the trait for yellow colour is dominant because a cross of the parents exhibiting this trait produces bright blue offsprings too, meaning that the genetic composition of the parents contains the gene that codes for yellow colour. Since these parents show a yellow colour in a heterozygous state, then the trait for yellow colour is dominant.

Therefore, the genotypes of the parents in each case include:

1. A bright blue female and a bright blue male produce all blue progeny. (bb × bb)

2. A yellow female and a yellow male produce a mix of both bright blue and yellow progeny (Bb × Bb)