Question

What are the four factors that drive the evolution of new adaptations? Describe each. Give a detailed example of each, including organism and genes and how these changed.

Answer 1

Evolution is the process reflecting the adaptations of organisms in response to the dynamic environment. Evolution of a population is the result of change in genotypic frequencies over long periods of time.

The factors responsible for evolution of new adaptations include:

A. Natural selection

B. Random genetic drift

C. Mutation

D. Population Mating structure

Natural selection : Natural selection is the process by which best adapted traits of organisms in a given population increase in frequency and are selected positively by nature.

Natural selection is usually indexed in terms of reproductive fitness which can be measured as absolute(raw no. Of genes which are transmitted with to next generation) or relative (absolute fitness of individual, genotype or phenotype/ absolute fitness of reference individual).

Natural selection occurs in three modes I.e. directional(eg. Evolution of Human brain size to 1300 and 1400 cc that is the result of doubling of size from Homo Habils and Homo Erectus) , stabilizing(eg.Human birth weight), disruptive(rare).

Natural selection results in the change in allele frequencies for eg. Change in genome frequencies of wolf genome.

Random genetic drift : It was first introduced by Sewall Wright. Random genetic drift is the phenomenon in which a portion of the population randomly drifts away resulting in poor gene pool as the drifting is solely by chance which leads to loss of some beneficial genes as well.

It depends on population size, the effect of genetic drift is minimum in large populations.

Genetic drift result in altered allele frequencies and fixation of 1 allele, decrease in number of heterozygotes.

For eg. Different alleles govern the beak size in birds, depending on the alleles present in the offsprings, other alleles drift away from population.

Mutation : Spontaneous Mutations are one the major force driving evolution as it results in more genetic variation and increases the evolution rates to many folds.

Mutations are considered as random and non directional.

For eg. Nonsense mutation in lacZ gene of E.Coli results in inhibition of synthesis of beta galactosidase enzyme ,therefore are lactose intolerant and are known as lactose auxotrophs i.e. second mutation result in reversing the affect of first(adaptive mutation)., Mutation in X chromosome of primates in genes of green and red retinal cone pigments resulting in colour discrimination.

Population Mating structure : Population is defined as a group of species which are capable of interbreeding and are residents of a same geographical area.

Population structure is mainly affected by geographical separation, immigration and emigration, founder effect and mate preference.

For eg.Horizontal gene transfer result in conferring antibiotic resistance to bacteria.