17.5 - Codominance And Multiple Alleles Flashcards

Question 1

Q

What is codominance, and how does it differ from simple dominance?

Answer

A

Codominance occurs when both alleles of a gene are equally dominant and are fully expressed in the phenotype.
Unlike the usual pattern of dominance and recessiveness, where one allele masks the expression of the other, in codominance both alleles contribute equally to the phenotype.
For example, in certain cattle, both red and white hairs are produced in heterozygous individuals, resulting in a roan coat color.

Question 2

Q

How does codominance manifest in shorthorn cattle coat colors?

Answer

A

In shorthorn cattle, one allele codes for the production of red pigment, while another codes for a non-functional enzyme, leading to white hairs. If both alleles are codominant:
1) Homozygous red (C^R C^R) produces red hairs, giving a red coat
2) Homozygous white (C^W C^W ) produces no pigment, leading to a white coat
3) Heterozygous (C^R C^W ) produces both red and white hairs, giving a roan (light red) coat.

BOTH PHENOTYPES ARE EXPRESSED

Question 3

Q

How are codominant alleles represented, and why can’t uppercase and lowercase letters be used?

Answer

A

Codominant alleles are represented by different letters as superscripts on a base letter representing the gene.
For example, in the case of cattle coat color, the base letter is C for colour
and the alleles are represented as… (the R for red pigment and W for no pigment)
Upper and lowercase letters cannot be used because this would imply that one allele is dominant over the other.

Question 4

Q

What are multiple alleles, and how many alleles can be present at a single gene locus?

Answer

A

Multiple alleles refer to the presence of more than two alleles for a gene.
However, because individuals have only two homologous chromosomes, they can only have two alleles at a given locus at any one time.
A well-known example of multiple alleles is the human ABO blood group system.