Question

LLL LULUI AL SOLULIUI 1. What are the four criteria (refer to your lecture notes) that must be met in order for natural selection to result in the evolution of a phenotypic trait? Also, explain why a trait evolves in a population as a result of these 4 criteria being met (in other words, provide a clear and detailed explanation of why the Irequency of a phenotypic trait would increase across generations as a result of these 4 criteria being met). 2. Explain directional, stabilizing selection, disruptive/ diversifying selection, and sexual selection. 3. Which of the following modes of natural section is acting in each of the following examples: stabilizing, disruptive, or directional selection? Use your textbook, lecture notes, internet, and critical thinking skills to figure these out. a) the evolution of color in the peppered moth popultion during from 1840 to 1900 in industrial areas of England (hint: see lecture notes).

Answer 1

1) The four criteria that must be  met in order for the natural selection to lead to the evolution of a phenotypic trait are as follows:

i) REPRODUCTION

ii) HEREDITY

iii) VARIATION IN FITNESS OR ORGANISMS

iv) VARIATION IN INDIVIDUAL AND TRAITS

EXPLANATION: In the struggle for existence individuals which are more fit are successful. Individuals who are more fit are successful. The individuals with more favourable adaptations will live a longer life and are able to win over their mating partner. In the struggle for existence, only those members survive which posses useful variations means nature selects fit individuals. This was called natural selection and it operates by differential survival and differential reproduction.

2) i) Directional selection: When a extreme phenotype is favoured over other phenotypes, and the number of the favoured phenotype increases in the population. This leads in the shifting of allele frequency in the direction of the favoured phenotype with time. This is known as directional selection.

ii) Stabilizing selection: Stabilizing selection means when a intermediate trait is favoured inspite of the extreme traits and the mean lies in the range of the intermediate trait. In this the natural selection will favour the survival of average phenotype.

iii) Disruptive selection: When natural selection selects for two or more extreme phenotypes, ans each phenotype is selected on the basis of there specific advantages. This increases genetic variation.

iv) Sexual selection: Sexual selection can be an intersexual selection in which members of one sex of one species choose mates of opposite sex for mating and reproduction, or it can be intrasexual in which there is direct competetion among individuals of one sex for mates of the opposite sex.

3) a) Directional selection

b) Disruptive selection

c) sexual selection

d) Directional selection

e) stabilizing selection