Question

1. what is codominance?
2. human blood types follow rules of codominance. what genotypes result in each of the following blood types?

ab –
a –
b –
o –

Explanation:

Question 14

Codominance is a genetic inheritance pattern where both alleles of a gene pair in a heterozygote are fully expressed, and neither allele is dominant or recessive to the other. For example, in human blood type AB, both A and B alleles are expressed, and the phenotype shows both A and B antigens on red blood cells.

• Blood type AB: In codominance, both A and B alleles are expressed. So the genotype must have both \( I^A \) and \( I^B \) alleles, so the genotype is \( I^A I^B \).
• Blood type A: The A blood type can result from having two A alleles (\( I^A I^A \)) or one A allele and one O allele (\( I^A i \)). This is because the O allele (\( i \)) is recessive, and when paired with \( I^A \), the A allele is expressed.
• Blood type B: Similar to blood type A, blood type B can be from two B alleles (\( I^B I^B \)) or one B allele and one O allele (\( I^B i \)). The B allele is expressed over the recessive O allele.
• Blood type O: For blood type O, the genotype must be two O alleles (\( ii \)) because the O allele is recessive, and only when both alleles are O will the O blood type (with no A or B antigens) be expressed.

Answer:

Codominance is a mode of inheritance in which both alleles of a gene in a heterozygous individual are fully expressed, with neither allele being dominant or recessive to the other, resulting in a phenotype that displays the traits of both alleles.

Question 15