book 9 (natural selection)

Question 1

explain why variation is important in natural selection

Answer 1

1. genetic variation may be caused by spontaneous mutations which creates new alleles and increases gene pool for natural selection to operate. this results in phenotypic variations in a given population which is needed for natural selection to act on. populations with variations are generally better adapted to changes in environment. different environments will have different selection pressures which selects for individuals who are more well-adapted to the environment have a selective advantage over those who are not. this results in individuals being able to survive till reproductive age and reproduce successfully, passing down alleles conferring advantageous characteristics to the next generation.

Question 2

explain how mutations leads to variations

Answer 2

gene mutations and chromosomal mutations involves alteration in DNA sequences that can result in formation of new alleles. the acquisition of new alleles increases the gene pool for natural selection

Question 3

explain how crossing over can lead to variations

Answer 3

crossing over between non-sister chromatids of homologous chromosomes during prophase I results in exchange of secretions of chromatids, leading to formations of new combinations of alleles on the chromosomes of the gametes.

Question 4

explain how independent assortment can lead to variations

Answer 4

independent assortment of homologous chromosomes occurs in metaphase I whereby pairs of homologous chromosomes arrange themselves independently at the equator of the spindle and subsequently segregation at anaphase I which results in different combinations of maternal and paternal chromosomes.

Question 5

explain how random fusion leads to variations

Answer 5

fertilisation is a random process whereby any female gamete can fuse with any male gamete to give rise to new combinations of allele in offspring, hence there is no zygotes with the same chromosome