(i) 1. Monohybrid Cross: A cross between two parents taking the alternative traits of one single character. For example, a cross between tall and dwarf pea plants.
2. Gene: Genes are the basic unit of heredity and are found on chromosomes. Each character or trait is controlled by one gene.
3. Phenotype: The observable character which is genetically controlled.
(ii) Two sex linked diseases in males are : Haemophilia and Colour blindness.
(iii) Mendel’s Law of Segregation: When Mendel performed cross-pollination between a true-breeding yellow pea plant and a true-breeding green pea plant, he noticed that all of the resulting offspring, F1 generation, were green.
He then allowed all of the green F1 plants to self pollinate. He referred to these off spring as the F2 generation. Mendel noticed a 3 : 1 ratio in pod color. About 3/4th of the F2 plants had green pea pods and about 1/4th had yellowpods.
From these experiments Mendel formulated what is now known as Mendel’s law of segregation. This law states that “allele pairs separate or segreagate during gamete formulation, and randomly unite at fertilization.