Linkage and Recombination I - Lecture 9

Question 1

Androgenic alopecia

Answer 1

Male pattern baldness
Trait is stimulated by male sex hormones (androgens)
Androgen-receptor gene on the X chromosome
Androgen receptor encodes a protein that binds male sex hormones

Question 2

Linked genes

Answer 2

Genes located close together on the same chromosome

Do not assort independently

Question 3

Linkage

Answer 3

Keeps particular genes together

Question 4

Crossing over

Answer 4

Mixes genes up

Question 5

Nonrecombinant Progeny

Answer 5

Gametes that contain only original combinations of alleles present in the parents

Question 6

Recombinant Progeny

Answer 6

Progeny display original combinations of traits found in parents

Question 7

For each meiosis in which a single crossover takes place:

Answer 7

Two nonrecombinant gametes and two recombinant gametes will be produced
*Same result as ind assortment

Question 8

When crossover between two loci takes place in every meiosis

Answer 8

It is impossible to determine whether the genes are on the same chromosome and crossing over took place or whether the genes are on different chromosomes

Question 9

For closely linked genes

Answer 9

Crossing over does not take place in every meiosis

Question 10

Maximum proportion of recombinant gametes is

Answer 10

50%

Question 11

Recombination Frequency

Answer 11

The percentage of recombinant progeny in a cross

(# of recombinant progeny/total number of progeny) x 100%

Question 12

Coupling

Answer 12

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

Question 13

Repulsion

Answer 13

One chromosome carries wild allele and a mutant and other carries other mutant and wild.
AKA trans
p+b/pb+

Question 14

Intermediate Linkage

Answer 14

In between the two extremes of ind assort and complete linkage. Occasional crossovers break up the linkage and allow genes to recombine.

Question 15

Interchromosomal Recombination

Answer 15

Between genes on different chromosomes. It arises from independent assortment occurring in anaphase I

Question 16

Intrachromosomal Recombination

Answer 16

Between genes located on dame chromosome. Arises from crossing over during prophase I of meiosis.

Question 17

For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because:

Answer 17

Each crossover takes place between only two of the four chromatids of a homologous pair

Question 18

The following test cross produces the progeny shown:
AaBb x aabb =
10 AaBb
40 Aabb
40 aaBb
10 aabb
Were the genes in the AaBb parents in coupling or in repulsion?

Answer 18

Repulsion