(a) Explain briefly how the process of meiotic division contributes to variation in a population
(b) State Mendel’s first and second laws of inheritance.
(c) A pure breeding brown coloured rat BB was crossed with a pure breeding white rat bb. By means of diagram only, show the genotypes of the offspring up to the second filial generation.
Explanation
(a)Process of meiotic division:
(i) In the prophase of first meiotic division, there is formation of chiasma. Variation occurs from the number and position of chiasmata formed. This determines the different combination that is possible in genes relative to the sequence of genes on the chromosomes.
(ii) In the metaphase of the first meiotic division, segregation of chromosomes occurs. This results in mixing of genes from different individuals carried on different chromosomes which now result in variation between parents and offsprings or among offsprings. Mixing of genes is known as crossing over.
(b)(1)Mendel's first law called law of segregation of genes states that characters of an organism are controlled by genes occurring in pairs which are independently transmitted in gametes from one generation to another without undergoing any alteration.
(ii) The second law known as independent assortment of genes states that character behaves as a separate unit and is inherited independent of another character.
