Question

1.4.2 test (cst): heredity
question 18 of 25
in cattle, the allele for white coat color (w) and the allele for red coat color (r)
are codominant. a heterozygote has the roan coat color. two cows with the
following genotypes are crossed.
ww × rr
what is the expected phenotypic ratio of the offspring?
a. 0 red: 4 roan: 0 white
b. 3 red: 1 roan: 0 white
c. 1 red: 2 roan: 1 white
d. 2 red: 0 roan: 2 white

Explanation:

Step1: Determine gametes

Parent 1 (WW) can only produce \(W\) gametes. Parent 2 (RR) can only produce \(R\) gametes.

Step2: Do the cross

Using Punnett - square (or simple combination), \(W\times R\) gives all \(WR\) offspring.

Step3: Determine phenotype

Since \(W\) and \(R\) are codominant, \(WR\) has roan coat color. So, 0 red (\(RR\)), 4 roan (\(WR\)), 0 white (\(WW\)).

Answer:

A. 0 red : 4 roan : 0 white