Theory question 104
Mendelian Inheritance(a) Explain briefly: (i) independent assortment of genes; (ii) the reason blood group O in humans can only exist in homozygous form while blood groups A and B can exist both in homozygous and heterozygous forms. (b) Complete the table below by naming the Classes of vertebrates in their evolutionary trend and giving one example each of the Classes.
Class of vertebrate | One example
Show the model answer
(a)(i) Independent assortment (Mendel's second law): when gametes form, the alleles of one gene separate into the gametes independently of the alleles of another gene (on a different chromosome), so all combinations of the alleles are equally likely in the gametes.
(ii) The allele for O is recessive to both A and B. A person shows group O only when both alleles are O (OO). The A and B alleles are dominant over O, so group A can be AA or AO and group B can be BB or BO.
(b) In evolutionary order, each with one example: Pisces (fish) – tilapia; Amphibia – toad/frog; Reptilia – lizard/snake/crocodile; Aves (birds) – domestic fowl/pigeon; Mammalia – human/goat/rat.
List the five classes from the oldest (fish) to the most recent (mammals).