1. A chicken heterozygous for the Creeper allele has a phenotype of shortened wi
ID: 80114 • Letter: 1
Question
1. A chicken heterozygous for the Creeper allele has a phenotype of shortened wings and legs. When looking at the phenotype, the Creeper allele is ___________ to the normal allele.
a) incompletely dominant
b) dominant
c) co-dominant
d) recessive
2. Geneotyping of a clutch of 98 chicks shows that 32 are normal and 66 are heterozygous for the Creeper allele. What would explain the lack of Creeper homozygotes being present in the flock?
a) the Creeper allele is co-dominant lethal
b) the Creeper allele is incompletely dominant lethal
c) the Creeper allele is dominant lethal
d) the Creeper allele is recessive lethal
Explanation / Answer
Answer 1: b) dominant (As explained below)
The shortened wings and legs are an abnormality called Creepers and not an expression as would be expressed in codominance or incompletely dominance where the genes collude to expressed intermediate traits or both traits equally. Creeper is a dominant gene where heterozygous chicken express the creeper phenotype.
Answer 2: c) the Creeper allele is dominant lethal (As explained below)
As explained above, creeper is a dominant gene where heterozygous chicken express the creeper phenotype. When a cross is conducted between two heterozygous chickens, one would expect three-fourth off-springs to be creepers and one-fourth to be normal, if one goes by the Mendelian principles. But instead you get two-thirds of creepers and one-third of normal chicken. This occurs because the homozygous creepers die because of lethality of the dominant homozygous.
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