Question

1. Which mechanisms can lead to adaptations in populations? Which can lead to speciation? [which of these is microevolution and which is macroevolution?]

2. What is fitness and which mechanism is it most associated with? Why is the concept of fitness important?

3. How do heterozygote advantage and indirect selection work? Why are they important? [think about deleterious alleles, too]

Answer 1

1. Change in the immediate environment and natural selection causes adaptations in populations. Mechanisms that lead to speciation are- geographical isolation, genetic drift, natural selection, reduction in gene flow and reproductive isolation.

Microevolution i.e change in allele frequencies that occurs over lesser time period occurs due to the following factors-  mutation, selection (natural and artificial), gene flow and genetic drift. Similarly, The basic evolutionary mechanisms such as mutation, migration, genetic drift, and natural selection can produce major evolutionary change if given enough time leading to macroevolution.

2. The word Fitness is used to describe how good a particular genotype is at leaving offspring in the next generation. This will only happen if the parental genotypic combination is good enough to impart a good combination of genes to its offsprings. Thus A genotype's fitness includes its ability to survive, find a mate, produce offsprings.

3. A heterozygote advantage describes the case in which the heterozygous genotype has higher relative fitness than either the homozygous dominant or homozygous recessive genotype. It is important because even a slight heterozygote advantage may act to increase the frequency of the mutant allele in the population, even if the mutant allele causes a major reduction in fitness in homozygotes in that population.

Indirect selection is a factor in the evolution of characters indirectly connected with those characters that undergo natural selection. For example, an increase in fertility is an indirect result of more intensive selection, which is as a rule accompanied by intensified elimination.