Exam 2: Linkage and recombination

Question 1

Pattern baldness

Answer 1

• Androgenic Alopecia
• mild thinning in women
• found on p12-22
• -region includes the androgen-receptor gene.
• -gene closely associated with inheritance of pattern baldness.

Question 2

Sturtevant

Answer 2

had the idea that variation in the strength of linkage might indicate how genes are positioned along a chromosome.

Question 3

Calvin Bridges

Answer 3

demonstrated that nondisjunction of X chromosomes was related to the inheritance of eye color in drosphila.

Question 4

Linked genes

Answer 4

• located close together on the same chromosome.
• belong to same linkage group.
• do not assort independently.

!NB! linkage keeps particular genes together.

Crossing over mixes up genes

Question 5

where does crossing over occur?

Answer 5

Meiosis I and is responsible for recombination.

Question 6

What structure would indicate that genes are typically independent (not linked)

Answer 6

a centromere between them

Question 7

What are the most common and Least common types of recombination

Answer 7

Most common: non-recombinant

Least Common: Double recombinant.

Question 8

why is the total percentage of recombinant gametes always half of the percentage of meioses in which crossing over takes place?

Answer 8

a single crossover affects only two of the four chromatids. Half of the gametes are recombinants and half are nonrecombinants. Max proportion of recombinant gametes is 50%.

Question 9

When linked genes undergo crossing some crossing over the result is mostly….

Answer 9

non-recombinant progeny and fewer recombinant progeny.

Question 10

How is recombination frequency calculated?

Answer 10

= # of recombinant progeny /total # of progeny x 100%

Question 11

Coupling:

Answer 11

WT alleles are found on one chromosome and mutant alleles are found on the other chromosome. AKA cis configuration p+b+/pb

Question 12

Repulsion:

Answer 12

one chromosome carries a wild allele and a mutant allele and the other carries the other wild and the other mutant. AKA Trans Configuration p+b/pb+

Question 13

In coupling, What are the most numerous progeny types?

Answer 13

those with either both WT or both mutant traits.

Question 14

In repulsion, what are the most number progeny types?

Answer 14

those with one WT and one mutant allele and those with the other WT and the other mutant allele