Linkage and Mapping in Eukaryotes

Question 1

What is linkage?

Answer 1

The tendency for genes or segments of DNA closely positioned along a chromosome to segregate together at meiosis, and therefore be inherited together

Question 2

What is the chance of chromosomes lining up at centre of a nucleus during meiosis and randomly associate in any of the potential combinations of heterozygous individuals?

Answer 2

Equal chance

Question 3

What is the chance of independent segregation of genes on different chromosomes?

Answer 3

Equal

Question 4

What is the chance of two genes on the same chromosomes lining up at centre of a nucleus during meiosis and randomly associate in any of the potential combinations of heterozygous individuals?

Answer 4

Certain, linkage

Question 5

What is way only way that two genes on the same chromosome will segregate two different chromosomes?

Answer 5

Recombination occur between genes during meiosis I

Question 6

How linkage discovered?

Answer 6

As in certain crosses, a greater number of offspring with ‘parental’ genotypes were generated than expected

Question 7

Who discovered linkage?

Answer 7

Bateson, saunders and punnent

Question 8

What indicated linkage?

Answer 8

A greater number of parental offspring than expected

Question 9

Where do non-parental genotypes arise from?

Answer 9

Crossing over during meiosis I

Question 10

What are non-parental genotypes called?

Answer 10

Recombinants

Question 11

What can be used to make linkage map of chromosomes ?

Answer 11

recombination

Question 12

What does the frequency of recombination and distance show?

Answer 12

The frequency of recombination between two genes will depend on distance between genes

Question 13

Finish the sentence:

The great the distance between two genes…

Answer 13

the greater the frequency of recombination

Question 14

What experiment did Morgan do?

Answer 14

Genetics of fruit fly Drosophila melanogaster

Question 15

What does one genetic map unit (m.u) show?

Answer 15

The distance between genes for which 1% products of meiosis are recombinant

Question 16

What is a map unit equal to?

Answer 16

centimorgan (cM)

Question 17

In a particular species of mammal black hair (B) is dominant to green hair (b) and red eyes (R) are dominant to white eyes (r). If a BbRr individual is mated with a bbrr individual the expected phenotypic ratio of the offspring is 1 black-red : 1 black-white: 1 green-red : 1 green-white. However, when you mate these individuals you find that the phenotypic ratio of the offspring is: black-red 450; black-white 50; green-red 50; green-white 450. Based on these data, what is the recombination frequency?

A) 5 %
B) 10 %
C) 20 %
D) 30 %

Answer 17

C

Question 18

What are genetic maps?

Answer 18

Linear and additive

Question 19

What are most common classes?

Answer 19

Parental types

Question 20

What are least common classes?

Answer 20

Recombinant types

Question 21

How to deduce gene order?

Answer 21

• Gene in the middle must be only one to undergo double recombination
• Double recombinants are found alongside alleles which is not found alongside in the parents