Lec 10-2

Question 1

Gene mapping

Answer 1

Specific genes location on the chromosome can be mapped

Question 2

Thomas Hunt Morgan

Answer 2

Used fruit flies to study chromosomes and their role in heredity

Hypothesized that crossing over was occurring all along the chromosome

Question 3

The further apart two genes are

Answer 3

The more likely there will be a crossover event

Physical distance between genes are proportional to recombination frequency

Question 4

Recombination frequencies could also tell you

Answer 4

Gene order

Question 5

Genetic maps

Answer 5

Chromosome maps calculated by using genetic phenomenon of recombination

Question 6

Genetic map distances are in

Answer 6

Map units (m.u)

One m.u. = 1% recombination rate

Question 7

1 map unit is also called

Answer 7

1 centiMorgan- in honor of Thomas Hunt Morgan

Question 8

Genetic distances are

Answer 8

Additive

Question 9

Physical maps are

Answer 9

Actual physical locations measured in actual bases along the chromosome

Question 10

Issues with gene mapping

Answer 10

Genetic mapping of genes far way from each other will give you an underestimate of the distance

This is due to double crossovers that are more likely to occur the farther apart they are

Thus, genetic maps based on short distance are more accurate

Question 11

Testcross between two genes is called a

Answer 11

Two-point testcross

Question 12

Constructing a map with two-point testcross

Answer 12

First see if you can split genes into linkage groups by looking for 50 % pairs

Pairs with 50% are not in the same linkage group

Anything that has a 50% recomb freq is in a different linkage group and is on a separate map

Things that are farther have a higher recomb frequency

If the numbers don’t add up, it is because the further away they are , the less accurate the distance is

Question 13

Three-point testcross

Answer 13

Test cross with three genes

More efficient to map 3 genes as it can be done with one cross rather than a series of two-point crosses

Question 14

Types of crossovers with 3 genes

Answer 14

Single crossover between gene A and B

Single crossover between gene B and C

Double crossover between A B and C

Question 15

Double crossover

Answer 15

Outer alleles are same as non-recombinants, but the middle alleles are recombinant

Question 16

Steps to determine gene order in a three-point cross

Answer 16

Identify the non-recombinant progeny (two most numerous phenotypes)

Identify the double-crossover progeny (two least numerous phenotypes)

Compare the phenotypes of double-crossover progeny with the phenotypes of nonrecombinant progeny.

The characteristic that differs between the double crossover and the nonrecombinant progeny is encoded by the middle gene

Question 17

Progeny types with low crossover is likely where

Answer 17

Double crossover occur

Probability of double crossover is much lower than single

Question 18

Determining gene order with a double crossover

Answer 18

Consider all three chromosome arrangements of the 3 genes and what happens after a double crossover

Which phenotype leads to the double crossover phenotypes being observed

Alternatively, look at the double crossover phenotypes and identify the gene that is different from the parents

This is the middle gene