2/18

Question

A roan cow shows co-dominance in fur color (orange & white). What is the phenotype ratio expected if a roan cow and a roan steer mate together?
1: Orange: 1 White
4: Orange and White
2 Orange: 2 Orange and White: 0 White
1: Orange: 2 Orange and White: 1 White
Q

Answer 1

In a scenario involving co-dominance, both alleles in a heterozygous genotype contribute to the phenotype. Let's denote the orange fur color allele as "O" and the white fur color allele as "W".

The genotype for a roan cow (which shows both colors) would be "OW" (heterozygous), while similarly the genotype for a roan steer would also be "OW". Therefore, when a roan cow (OW) mates with a roan steer (OW), we can analyze the potential offspring using a Punnett square:

        O     W
     ----------------
  O |   OO   |  OW   |
     ----------------
  W |   OW   |  WW   |
     ----------------

From the Punnett square, the possible genotypes of the offspring are:

• OO (homozygous orange)
• OW (heterozygous roan)
• OW (heterozygous roan)
• WW (homozygous white)

This results in the following offspring ratio:

• 1 OO (Orange)
• 2 OW (Roan)
• 1 WW (White)

Thus, the phenotype ratio of the offspring will be:

• 1 Orange: 2 Roan: 1 White

Therefore, the expected phenotype ratio if a roan cow and a roan steer mate together is 1: Orange : 2: Orange and White : 1: White.