Lecture 4

Question 1

What is pleiotropy?

Answer 1

One gene causes different traits.
Example: sickle cell anemia causes abnormal Hb and joint pain
Example: yellow coat color and lethality in mice

Question 2

What are characteristics of a metabolic pathway? Example?

Answer 2

Pathway includes multiple steps, intermediates, and enzymes meaning multiple genes are involved.
Example: Neurospora, created multiple mutants and studied growth of mutants in response to supplements to establish order of biosynthetic pathway. Supplements rescue mutations in earlier steps.

Question 3

What are characteristics of a regulatory pathway? Example?

Answer 3

Pathway includes chain of proteins transmitting environmental signal to gene expression. A defect in ONE step would have same effect of no signal response. Defects in early steps mask defects in later steps.
Example: yeast response to mating pheromone, receptor binds hormone > activates g protein > autophosphorylation > etc.
Example: embryonic development

Question 4

What are four different ways to investigate gene interactions?

Answer 4

1. Mutagenesis and intercross until true breeding
2. Backcross or test cross
3. Selfing
4. Test for allelism

Question 5

What is a test for allelism (complementation test) in diploids?

Answer 5

Finding out whether mutations are in the same or different genes.
Example: if two genes are needed to make blue flowers, then if white mutants with a defect in the same gene are crossed you will never see blue flowers. If mutants with a defect in different genes of the two then you will see blue flowers (restore WT).

Question 6

How do you test for allelism in haploids (fungi vs bacteria)?

Answer 6

Fungi: dikaryons, multinucleated cells
Bacteria: make a haploid organism diploid for certain genes by inserting a plasmid with genes on interest on it. Will help to see if mutation is in those genes inserted.

Question 7

What does a 9:3:3:1 ratio indicate?

Answer 7

No interaction between genes

Question 8

What does a 9:7 ratio indicate?

Answer 8

Duplicate recessive gene
Defect in either gene leads to same mutant phenotype
9: A-B-
3,3,1: aaB-, A-bb, aabb

Question 9

What does a 9:3:4 ratio indicate?

Answer 9

Recessive epistasis: when a single mutant has a distinct phenotype and the double mutant has same phenotype as one of the mutants
9: A-B-
3: aaB-
3,1: A-bb, aabb (bb makes aa look like A-, bb is epistatic over aa and A-)

Question 10

What does a 12:3:1 ratio indicate?

Answer 10

Dominant epistasis: when a dominant allele is epistatic

9,3: A-B-, aaB- (B- makes aa look like A-, B- is epistatic over aa and A-)

Question 11

What does a 13:3 ratio indicate?

Answer 11

Suppression
9,3,1: A-B-, A-bb, aabb (bb suppresses aa phenotype to make it look like WT)
3: aaB-

Question 12

What does a 15:1 ratio indicate?

Answer 12

Duplicate dominant genes
Example: Each gene alone makes same phenotype, so only one of two genes is needed to make particular phenotype
9,3,3: A-B-, A-bb, aaB-
1: aabb

Question 13

What does a 9:6:1 ratio indicate?

Answer 13

Duplicate genes with cumulative effect
Having one dominant allele from either gene produces same phenotype. Having dominant allele from each gene produces a different phenotype.
9: A-B-
3,3: aaB-, A-bb
1: aabb

Question 14

What does epistasis mean?

Answer 14

The interaction between two or more genes to control a single phenotype