Mendel's Laws and Beyond - Lecture 10

Question 1

What is Mendel’s first law?

Answer 1

Members of the gene pair segregate equally into gametes, so that each gamete has only one of the two genes

Question 2

What is Mendel’s second law?

Answer 2

Different genes assort independently in gametes

Question 3

What is the nature of a mutant allele with a loss of function?

Answer 3

Recessive

Question 4

What is the nature of a mutant allele with a gain of function?

Answer 4

Dominant

Question 5

What is incomplete dominance?

Answer 5

Heterozygote phenotype is intermediate between the two homozygote phenotypes e.g. LDL receptor gene

Question 6

What is co-dominance?

Answer 6

Heterzygotes show phenotype of both alleles e.g. AB blood group

Question 7

What are multiple alleles?

Answer 7

○ More than two alleles for a gene
○ Dominance/recessiveness is a relationship between two alleles

Question 8

What is pleiotropy?

Answer 8

○ A gene can influence more than one trait
○ If a specific molecular function of a protein is reused in different cellular contexts, a mutant form of this protein is likely to lead to pleiotropy

Question 9

What are lethal alleles?

Answer 9

Cause skewed phenotypic ratios

Question 10

What does penetrance measure?

Answer 10

The percentage of individuals with a given genotype who exhibit the expected phenotype

Question 11

What does expressivity measure?

Answer 11

The extent to which a given genotype is expressed at the phenotypic level e.g. very yellow fur, slightly yellow fur

Question 12

What is Alfred Knudson’s two hit hypothesis?

Answer 12

○ Explains incomplete penetrance in familial cancer syndrome
○ First hit: Inherited mutation in one copy of the tumour suppressor gene and is present in all cells and passed down
○ Second hit: A somatic mutation (during the person’s lifetime) occurs in the second copy of the same tumor suppressor gene, leading to a complete loss of its function