(a) "Proteins control the expression of various characters." Explain this statement by taking an example of "tallness" as a characteristic in plants. OR (b) Explain the mechanism of inheritance used by sexually reproducing organisms to ensure the stability of DNA of the species.

(a) Proteins control the expression of various characters by regulating the amount of a particular hormone or enzyme. For example, in plants, the amount of a particular plant hormone determines the height of the plant. If the gene for the enzyme that makes this hormone is altered, the amount of hormone will be less, and the plant will be short. (b) Sexually reproducing organisms use a mechanism of inheritance that ensures the stability of DNA of the species. Each cell has two copies of each chromosome, one from each parent. Every germ cell takes one chromosome from each pair, which may be of either maternal or paternal origin. When two germ cells combine, they restore the normal number of chromosomes in the progeny.