Question

1. Below is a list of several scenarios that have occurred in our natural world. Read the situation carefully and identify the type of selection taking place. Explain why you choose your answer.

Stabilizing selection               Genetic Drift

Directional selection              Heterozygote Advantage

Disruptive selection               Bottleneck

Founder effect                        Underdominance

A) After a chemical plant moves into town near a meadow, local downwind populations of plants begin to adapt to the resulting air pollution. Scientists document that the acid rain tolerance of several plant species has increased significantly in the polluted area.

B) The northern elephant seal population was reduced to over hunting to 20 individuals in the 1890’s. Although the population has rebounded to over 30,000 individuals now, scientists discovered that 25 gene loci were homozygous.

C) Cystic fibrosis is an inherited disease caused by an autosomal recessive allele. Homozygous individuals usually die by the age of 35 of lung infections. However, there is some evidence that heterozygotes are more resistant to typhoid or cholera.

D) African butterfly species Pseudacraea eurytus, utilizes Batesian mimicry to escape predation. This species possesses two alleles which each confer an appearance similar to that of another local butterfly species that is toxic to its predator. Individuals who are heterozygous for this trait experience increased predation.

E) Two populations of fish are separated by a strip of land that divides the lake into two bodies of water. For all practical purposes each side of the like is identical; the selective pressures are identical. Over time the populations become quite different.

F) The Afrikaner population of the descendants of Dutch settlers in South Africa has an unusually high frequency of the gene that causes Huntington’s disease.

Answer 1

ANS A.GENETIC DRIFT

Drastic changes in environmental conditions can sometimes cause drastic changes to the gene pool of the population. In this example allele frequency of a plant species are changes due to changes in environment condition.

ANS B. Bottleneck Effect

The bottleneck effect is an extreme example of genetic drift that happens when the size of a population is severely reduced. for atleast one generation by some disasters. in this example the population of northern elephent reduced by overhunting.

ANS C. heterozygote advantage

A heterozygote advantage describes the case in which the heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype.

ANS D. An example of stable underdominance

Underdominance exists in situations where the heterozygotic genotype is inferior in fitness to either the dominant or recessive homozygotic genotype. This example of underdominance is stable because any shift in equilibrium would result in selection for the rare allele due to increased resource abundance.

ANS E. Genetic drift

the example with the exact same selective pressures is the only scenario that could result in genetic drift. Sources of food can also cause an organism to change. For instance, if on one side of the lake the dominant food source is algae and on the other side smaller, quicker fish are the source of food, then over time the fish on either side of the hypothetical lake could diverge. One gaining a better ability to scoop algae and the other becoming very agile.

ANS F. founder effect.

The case of Huntington's disease in South Africa provides a striking example of the founder effect. The Afrikaner population of South Africa is mainly descended from one .The early colonists included individuals with a number of rare genes.