Week 4

Question 1

In humans, the allele for “attached” earlobes is recessive to the allele for “free” earlobes, and the allele for “straight” hairline is recessive to the allele for “widow’s peak” hairline. A man who is heterozygous at both loci has a large family with a woman who is homozygous at both loci and has a “straight” hairline and “free” earlobes. Approximately what proportion of their children would we expect to have which phenotypes?

Answer 1

100% of the children would have free earlobes, 50% would have a straight hairline

Question 2

Define heterozygote in genetic terms

Answer 2

Having one dominant allele and one recessive allele

Question 3

3) If you suffer from an extremely rare genetic disease that is caused by a recessive allele at a single locus, and neither your parents nor your brother have this disease, what is the probability that your brother is a carrier (heterozygous at this locus)?

Answer 3

2/3

Question 4

4) If half the members of a population have the phenotype of the dominant allele, and half have the phenotype of the recessive allele, which allele at this locus is probably more common in the population?

Answer 4

Recessive