Chapter 7

Question 1

Define linked genes

Answer 1

Genes on the same chromosome

Question 2

2. Know that genes at different loci can be:

Answer 2

 on different chromosomes –assort independently
o Solve like we have been solving in previous chapters
 on the same chromosome and completely linked -
o genes are so close together on the same chromosome that always travel together into a gamete (do not
sort independently)
 on the same chromosome and incompletely linked
o genes sometimes travel together into a gamete, but can also be separated through a crossing over event
(do not sort independently)

Question 3

3. Know how to determine if genes are assorting independently

Answer 3

 in Fig 7.2, the F2 are not in a 9:3:3:1 ratio so it does not appear that they are assorting independently

Question 4

4. Know the notation for crosses with linkage

Answer 4

As arranged on each chromosome-
A______B x a______b
A______B a______b

Question 5

5. Know how to calculate recombination frequency

Answer 5

recombinant/total * 100%

Question 6

6. Understand
    when a crossover occurs, only the ____________ are involved in the crossover
    therefore, with a single crossover between 2 genes, 50% of the gametes will be ___________ (and
   50% will be ___________ )
    this means that if a crossover occurred between those 2 genes every time that meiosis occurred, 50% of the
   gametes will be ____________
    therefore, the maximum recombination frequency is ___

Answer 6

middle chromatids, recombinant, nonrecombinant, recombinant, 50%

Question 7

7. Differentiate between coupling (cis configuration) and repulsion (trans configuration)

Answer 7

Coupling- WT alleles on one chromosome, mutant on the other
Repulsion-Each chromosome has one WT, 1 mutant allele

Question 8

8. Know the notation for coupling and repulsion

Answer 8

Coupling- AB—ab
Repulsion- Ab—aB

Question 9

9. Understand how the configuration of alleles (whether they are cis or trans) can change the progeny phenotypic
   ratios

Answer 9

Recombinant and nonrecombinant gametes are flipped, so that changes progeny ratios (because during crossing over you’re crossing AA aa instead of Aa Aa)

Question 10

Different chromosomes-

Answer 10

assort independently, combine randomly. Heterozygote at 2 loci make 4 gametes in equal proportions (Aa Bb, aa bb, Aa bb, aa bb)

Question 11

11. Be able to predict the proportions of offspring expected when the recombination frequency is given

Answer 11

Probability of inheriting gamete 1 times ptobability of gamete 2

Question 12

12. Understand the relationship between crossing over and genetic maps:

Answer 12

 crossing over occurs randomly
 2 genes far apart are more likely to crossover than 2 genes close together
 distance between genes is proportional to recombination frequency
 this allows us to create a genetic map measured in map units
 1% recombination = 1 map unit = 1 centi-Morgan

Question 13

13. Define three-point testcross

Answer 13

 testcross involving three linked genes
 better than two-point testcrosses because only 1 cross is needed rather than multiple two-point testcrosses–
also two-point testcrosses can miss double crossovers

Question 14

14. Understand how to create a genetic map from a three-point testcross. Here are the steps:

Answer 14

1. Determine gene order
2. Rewrite genes in correct order
3. Locate crossovers
4. Calculate recombination frequencies
5. Construct gene map
6. Calculate coefficient of coincidence
7. Calculate interference

Question 15

Linkage with some crossing over-

Answer 15

Nonrecombinant more than 50 percent, recombinant less than 50 percent

Question 16

Complete linkage-

Answer 16

nonrecombinant only