Question

2. You're a beta fish breeder and have noticed that you have a few fish that display a totally novel ruby red coloring pattern. This ruby red color has since become is very popular in your Etsy store, but you are STRUGGLING to develop a purebreeding strain. Like, every time two ruby red betas are crossed, you end up with a fair number of ruby reds, but still a significant number of betas featuring the standard-type coloration. In your most recent ruby red x ruby red mating attempt, you ended up with 57 ruby red betas and 28 standard betas. All other such matings gave similar phenotypic offspring ratios. Explain what's going on here. (<4 sentences)

Answer 1

Before solving this problem let us summarise key points:

1. A novel ruby red coloring pattern was noticed.

2. Unable to develop a pure breeding strain.

3. When two ruby red betas are crossed very few ruby reds are obtained. Betas with standard type coloration were also observed.

4. Recent ruby red X ruby red gave 57 ruby red betas and 27 standard betas. This was the most occurring phenotype in this cross.

Now let's solve the problem:

1. This problem is based on lethal genes. Lethal genes carry mutations and in this problem, the gene responsible for ruby red is a dominant lethal gene.

2. Let us consider the alleles for ruby red as heterozygous dominant "Rr" and the alleles for standard type as homozygous recessive "rr". Dominant lethal gene, in this case, will be RR.

2. In the given problem a cross was made between two ruby reds. Their genotype would be as follows:

Rr X Rr =

RR, Rr, Rr, rr

RR dominant lethal phenotype will not survive. Hence the effective genotype ratio would be 2:1.

The phenotype mentioned in the problem is 57:28 which is roughly equal to 2:1. Hence, whenever ruby red fishes are crossed there is a reduction in the number of ruby red betas due to the activity of a homozygous dominant lethal gene (RR).