Topic 10 pt 2: Mapping

Question 1

What did Thomas Hunt Morgan do

Answer 1

Developed the idea that physical distance between linked genes are related to their recombination rates

Question 2

Genetic map vs physical map vs map units

Answer 2

Genetic map: generated using RF

Physical map: actual physical distance in bp

Map units: centiMorgans (cM), 1cM = 1 RF (for genetic maps)

Question 3

What can we not distinguish between in terms of recombination

Answer 3

Unlinked genes on different chromosomes and unlinked genes that are just very far apart on the same chromosome

Question 4

Parental/recombinant ratio in progeny for unlinked gene

Answer 4

50/50

Question 5

When will mapping distance be underestimated? Why?

Answer 5

For genes that are far apart but linked
Due to double cross overs between them (slide 7)

Question 6

Slide 8, 10

Answer 6

Linkage and non linkage, genetic map calculation

Question 7

Why construct a genetic map with a three-point testcross (4)

Answer 7

1. more efficient mapping technique
2. order of the three genes can be established in a set of progeny
3. some double crossovers can be detected
4. more accurate map distances

Question 8

Slide 13-16

Answer 8

Genetic map with three-point testcross

Question 9

Steps in determining gene order in a three point cross (4)

Answer 9

1. Identify the nonrecombinant progeny (two most numerous phenotypes)
2. Identify the double-crossover progeny (two least numerous phenotypes)
3. Compare phenotypes of double crossover and nonrecombinant progeny. Should be alike in two characteristics and differ in one.
4. Characteristic that differs btw nonrecombinant and double crossover progeny is encoded BY THE MIDDLE GENE

Question 10

Slide 20***

Answer 10

RF calculations