Question

Q1. You have considered single locus and two locus (di) hybrid crosses for loci with alleles that are completely dominant/recessive.

1. Come up with a general rule for the proportion of offspring expected to have the phenotype of all the recessive traits associated with X autosomal loci when fully heterozygous parents are crossed.

2. Now, use that logic and provide the expected proportion of offspring that show recessive phenotype for 4 loci and the dominant phenotype the 5th locus when two fully heterozygous parents are crossed.

Q2. Adaptive evolution depends upon mutations to generate genetic variation. Yet, evolutionary theory predicts that mutations are random and yet most mutations are harmful (deleterious) or have no effect (neutral). Explain this apparent paradox drawing upon your knowledge of genomic elements and gene structures. Does changing the mutation rate (for example, by exposure to mutagens) alter these expectations? Defend your argument.

Q3. Sickle cell anaemia: The selective forces that a population experiences can vary by context, especially by geographic place.

a. Explain how natural selection affects the evolution of haemoglobin in humans and how and why theselectivepressuresdifferamonghumanpopulations. UseAfricaandEuropeasexamplesof human populations, give genotypes and explain selective pressures.

b. Is natural selection on haemoglobin in African populations best described as disruptive, stabilizing or directional selection?

c. Is natural selection on haemoglobin in Australian populations (no malaria) best described as disruptive, stabilizing or directional selection?

d. For human populations living in Australia (no malaria), do you expect the Hs allele to eventually go extinct? Explain why or why not.

Answer 1

1. 2. The neutral and nearly neutral theories of molecular evolution differ from each other as a means for determining causal processes associated with random drift and natural selection.

Yes, changing the mutation rate (for example, by exposure to mutagens) alter these expectations.

For example,a large fraction of mutations is deleterious, any anthropogenic increase in mutation rates from mutagenic pollution will have serious effects.

3 a.Natural selection causes evolution of haemoglobin in human. It is caused by a mutation in the normal allele (A) for hemoglobin.