TOPIC 4

Question 1

what is the expected frequency of phenotypes in a dihybrid cross?

Answer 1

9:3:3:1

Question 1

what is the expected frequency of phenotypes in a tester cross with a dihybrid

Answer 1

1:1:1:1

Question 2

crossing over occurs between _____ (sister chromatids or non-sister chromatids or chromosomes)

Answer 2

non-sister chromatids

Question 3

at what stage does recombination occur

Answer 3

prophase I

Question 4

what happens when sister chromatids have crossovers

Answer 4

nothing, they have the same alleles so no new combinations would be made

Question 5

what are recombination hotspots?

Answer 5

locations where recombination occurs more frequently than expected

Question 6

what are recombination blocks?

Answer 6

locations where recombination occurs less frequently than expected

Question 7

why do we use only females as the dihybrid for Drosophila

Answer 7

because crossing over does not occur in males bc in prophase I they have no synaptonemal complexes

Question 8

does recombination frequency differ between male and female humans?

Answer 8

yes, females have higher recombinant freq

Question 9

what are syntenic genes

Answer 9

genes on the same chromosome

Question 10

what are linked genes

Answer 10

genes that are close enough to each other to disrupt independent assortment (they dont assort independently)

Question 11

what is the expected frequency of recombinants and parental in independent assortment

Answer 11

50% each

Question 12

what causes recombinant gametes

Answer 12

crossing over

Question 13

what is a cross-shaped structure that form during meiosis that is an evidence of crossover occuring

Answer 13

chiasmata

Question 14

what is the purpose of a three gene testcross

Answer 14

to determine gene order and distance of 3 genes

Question 15

what is the dF when youre checking the linkage of 2 genes using the complicated chi square method

Answer 15

dF=1

Question 16

what do abbarent ratios (2:2:2:2 or 2:4:2) indicate

Answer 16

that crossing over occured between genes

Question 17

what do abbarent ratios (6:2,5:3,3:1) indicate

Answer 17

gene conversion (crossing over within the gene)

Question 18

after both strands of a chromatid break in the same location what end is eroded and what end is left

Answer 18

5’ end is eroded and 3’ end is left

Question 19

what is a heteroduplex region

Answer 19

when strand displacement in crossing over spans a site of heterozygousity

Question 20

what happens when you cut a holiday junction vertically

Answer 20

you get heteroduplexes and recombinants

Question 21

what happens when you cuy a holiday junction horizontally

Answer 21

you get no recombinants

Question 22

what is a holiday junction

Answer 22

double strand crossovers

Question 23

if heteroduplex spans homozygous site what is the outcome

Answer 23

no recombination

Question 24

if heteroduplex spans heterozygous site what is the outcome

Answer 24

recombinants

Question 25

what is formed when the one single-strand tail invades the non sister chromatid

Answer 25

a hetroduplex displacement loop (D-loop)

Question 26

one strand correction for allele conversion

Answer 26

5:3

Question 27

two strand correction for allele conversion

Answer 27

6:2

Question 28

no correction allele conversion

Answer 28

3:1:1:3