Question

A pet shop is breeding neon tetra fish and find some interesting color phenotypes.

1. The breeder crosses a true-breeding red neon tetra to a true-breeding yellow neon tetra and finds that all F1 progeny are red. Crossing two F1 red neon tetras results in the following numbers of progeny: 36 Red neon tetras, 3 Yellow neon tetras, and 9 Orange neon tetras. How many genes are involved in neon tetra coloration?

a. 1

b. 2

c. 3

d. 4

e. Cannot be determined from the information given

2. Which of the following genotypes produce Red neon tetras?

a	A_ B_
b.	A_ bb
c.	aa B_
d.	aa bb
e.	Both A_ B_ and aa B_ genotypes
f.	Both A_ bb and aa B_ genotypes
g.	None of the above 3. If a Red F2 neon tetra is crossed to a Yellow F2 neon tetra, what is the probability that they will produce Orange offspring?

Answer 1

1.

Red = Dominant = R_N_ or rr N_

Yellow = Recessive = rrnn

Orange = R_nn

Parental cross: RRNN X rrnn

F1 Progeny = RrNn = All red

F1 selfing: RrNn X RrNn

Phenotypic ratio = 36 red : 3 yellow : 9 orange

Phenotypic ratio = 12 red (R_N_ or rr N_) : 1 yellow (rrnn) : 3 orange (R_nn)

This is dominant epistasis ratio. A dominant allele at one locus is sufficent to mask the effect of recessive alleles at the other locus.

Number of genes involved = 2 (Four alleles)

Red neon tetra genotype = A_B_ and aaB_

So, option F is correct.