Chapter 15 Heridity II

Question 1

State the type of variation shown by eye colour. [1] (2013/A6)

Answer 1

Discontinuous variation

Question 2

With reference to the inheritance of ABO blood group phenotypes, explain what is meant by co-dominance [6] (2017/B10 Oa)

Answer 2

In co-dominance, two alleles are equally dominant in heterozygous
genotype and will exert/ expresses its effects equally on the phenotype of organisms. [1]
In ABO blood group, both IA and IB alleles are codominant [1] and are dominant to IO allele which is a recessive allele. [1]
When a person have one IA allele and one IB allele, both alleles exert their effects equally on the phenotype, thus the person will have blood group AB. [1]
A person with two IA alleles or one IA allele and one IO allele will have blood group A . A person with two IB alleles or one IB allele and one IO allele will have blood group B.[1] A person, homozygous recessive, with two IO alleles will have blood group O.[1]