Lecture 9/21 - E2

Question 1

Steps on how to use genetics to define a biochemical pathway

Answer 1

1. Identify mutants defective in the synthesis of a particular compound
2. Define the number of genes present in the mutant set by complementation analysis
3. Determine the order of gene function in this biosynthetic pathway using purified metabolic intermediates

Question 2

In a biosynthetic pathway where a step is blocked, which molecules accumulate and which molecules grow?

Answer 2

The precursors are accumulated while the downstream molecules grow

Question 3

Complementation Analysis

Answer 3

A test used to determine if two mutations giving the same phenotype are alleles of the same gene or in two different genes

Question 4

What do the + and - mean with the complementation analysis?

Answer 4

\+ = there is complementation between 2+ genes
- = there is no complementation

Question 5

How do you determine if two true-breeding recessive mutants for white eyes have mutations in the same gene or two different genes?

Answer 5

If the F1 offspring have white eyes, mutations are in the same genes with no complementation.
If the F1 offspring have WT red eyes, mutations are on different genes with complementation.

Question 6

How do you determine the number of different complementation groups present based on pairwise genetic cross data?

Answer 6

Ones on the same row that have minus signs are complementary. Go through each row to see how many sets of minus signs.

Question 7

What is the phentoypic ratio for a dihybrid cross that produces offspring that display the WT phenotype for a trait with a dominant allele for the specific trait?

Answer 7

9:3:3:1
DD: DR: RD: RR

Question 8

What is the phentoypic ratio for a dihybrid cross that produces offspring that display the WT phenotype only when both genes are dominant?

Answer 8

9:7
(WT) DD: (Mutant) DR, RD, RR
Genes act in sequence at two independent biochemical steps, in order to complete the pathway, both steps are required

Question 9

What is the phentoypic ratio for a dihybrid cross that produces offspring that display the WT phenotype when either dominant allele causes WT for both traits?

Answer 9

15:1
DD, DR, RD : RR
WT: Mutant
Two genes encode the same activity so either can do the job to produce WT

Question 10

What is the phentoypic ratio for a dihybrid cross that produces offspring that where the heterozygotes have the same intermediate mutant phenotype?

Answer 10

9:6:1
DD: DR, RD : RR
Both dominant alleles are needed for WT phenotype, recessive allele for either trait produces the same intermediate phenotype, and homo recessive produces a third phenotype

Question 11

What is the phentoypic ratio for a dihybrid cross that produces offspring where one allele homo recessive blocks the other trait?

Answer 11

9:3:4
DD: RD: DR, RR
One gene controls whether the other can be effective. Example: bbE- produces brown while B-ee produces yellow mutant because you can’t move pigment into the hair with no E function

Question 12

What is the phentoypic ratio for a dihybrid cross that produces offspring where one dominant allele blocks pigment production

Answer 12

12:3:1

DD, DR : RD : RR

Question 13

What is the phentoypic ratio for a dihybrid cross that produces offspring where certain dominant alleles suppress the other?

Answer 13

13:3

DD, RD, RR : DR