(i) (1) Mutation: Sudden changes in one or more genes in the progeny, which normally may not have existed in the parents, grand parents or even great grand parents. Example: Albinism (total loss of skin pigment).
(2) Homologous Chromosomes: A pair of corresponding chromosomes of the same Size and shape, one from each parents.
(3) Alleles: Allele is the alternative form of a gene occupying the same position on a chromosome and affecting the same characteristic but in two alternative ways. Example : The free and attached ear lobe alleles of the ear lobe character.
(ii) Dihybrid Ratio: The dihybrid ratio is 9 : 3 : 3 : 1. Mendel’s 3rd law i.e., ‘Law of Independent Assortment’ explains the dihybrid ratio. This law states that when there are two pairs of contrasting characters, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.
(iii) The three main reasons for the sharp rise in human population in the world are as follows:
(1) Better health care: There are more health care centres, hospitals and practicing doctors available for help to all age groups.
(2) Food shortages minimized: Due to green revolution, more food is produced and stored. There are very few starvation deaths.
(3) Large scale immunization: There has been large scale immunization against fatal diseases, to protect the infants from death.
