In horses, the extension gene helps determine coat color. The dominant trait (E) produces black pigment in the coat. The recessive trait (be) produces red pigment. Would a cross between a stallion who is homozygous, (EE), and a mare who is heterozygous (Ee) ever produce a red foal?

Answer 1

To determine whether a cross between a homozygous stallion (EE) and a heterozygous mare (Ee) could produce a red foal, we need to analyze the genetics of the trait.

• The stallion's genotype is EE, which means he can only pass on the dominant allele (E) for black pigment.
• The mare's genotype is Ee, meaning she can pass on either the dominant allele (E) or the recessive allele (e).

When we set up a Punnett square for this cross, we get the following possible combinations of alleles for their offspring:

• The stallion (EE) can only contribute E.
• The mare (Ee) can contribute either E or e.

Now, the combinations from the cross would be:

1. EE (from E of stallion and E of mare)
2. Ee (from E of stallion and e of mare)

This results in:

• 50% of the foals being EE (black coat)
• 50% being Ee (also black coat since E is dominant over e)

Since red pigment is produced by the genotype (ee), and neither parent can provide two recessive alleles (the stallion cannot provide any e), it is impossible for this cross to produce a foal with the genotype ee.

Therefore, a cross between a homozygous stallion (EE) and a heterozygous mare (Ee) will never produce a red foal.