(a) (i) Define the law of independent assortment.
(ii) State the findings from Mendel’s experiment involving white-flowered and red-flowered pea plants.
(iii) Illustrate these findings by means of simple diagrams.
(b) Explain why blood groups A and B in man can exist both in heterozygous and homozygous conditions while blood group 0 can only exist in homozygous state. .
Explanation
(a) (i) The law of independent assortment states that each member of alleles or contracting character may combine randomly with either member of another pair.
(ii) Findings of Mendel's experiment involving white and red flowered pea plants:- On crossing white and red flowered pea plants, he obtained all red - flowered offspring, but on self-.crossing each of these red- flowered plants he obtained mixtures of red flowered and white flowered plants in the ratio of 3:1 (¾ red / ¼ white flowered).
(iii) Illustrations: Key for parental genotype e.g R for red, r for white
(b) Blood grouping in man is determined by three alternative genes (alleles) A, B, and 0. A person can only possess two (alleles) of the genes on a pair of homologous chromosomes. 0 is recessive to both A and B, hence it is possible to have blood group A and AA (homozygous) and AO (heterozygous) and group B as BB or BO. However, group 0 can only exist genotypically as 00 in the homozygous recessive state.