Question

A. Which type of mutation do you feel would be most likely to be influenced by natural selection, those that result in changes of the third codon position, or those that result in changes of the first codon position? Explain your reasoning.    

B. In many animals inbreeding among close relatives reduces the ability of their offspring to survive. Explain why this occurs.

Answer 1

Qa) Mutation occuring in the first codon position gets affected by Natural selection, because these are the coding regions and the Coding regions are usually get affected by natural selection, but segments of DNA which do not code for proteins (or non-coding regions) are less prone or are less affected by natural selection. Mutation accumulates faster in noncoding regions, and causes them to evolve rapidly. Due to degeneracy of the genetic code, mutation in third codon position do not influence the amino acid composition of the protein for which a gene codes. So third codon mutations are usually neutral and they accumulate more rapidly than the first or second position, so changes in first codon position is most likely get influenced by natural selection.

Qb) Homozygosity (presence of identical alleles of the gene on both homologous chromosomes) occurs due to Inbreeding. This increases the chances of offspring to be affected by recessive or deleterious traits. Due to this there is a decreased biological fitness in a population( it is called inbreeding depression), that is the ability to survive and reproduce gets reduced. By continuous inbreeding, genetic variation is lost and homozygosity increases. It increases the expression of recessive deleterious alleles in homozygotes.