Genetic Linkage and Mapping

Question 1

What are syntenic genes?

Answer 1

Genes located on the same chromosome

Question 2

What are linked genes?

Answer 2

Syntenic genes that are so close together that their alleles cannot sort independently.

Question 3

What are recombinant chromosomes

Answer 3

Chromosomes whose syntenic genes have been reshuffled between homologs during crossing over

Question 4

What are parental chromosomes?

Answer 4

Homologs that do not reshuffle alleles under study

Question 5

What is genetic linkage mapping?

Answer 5

Plots the positions of genes on chromsomes?

Question 6

When does independent assortment of syntenic genes occur?

Answer 6

If they are far apart on a chromosome so that recombination occurs very frequently

Question 7

What are the characteristics of linked genes?

Answer 7

Are always syntenic and always located near one another

Question 8

Does genetic linkage lead to the production of more gametes with parental allele combinations or nonparental combinations?

Answer 8

Parental

Question 9

Is crossing over more likely to occur between closely linked genes or those further apart on a chromosome?

Answer 9

Farther apart

Question 10

How can genetic linkage be recognized?

Answer 10

By comparing observed frequencies of gamete phenotypes or progeny phenotypes with those expected under independent assortment

Question 11

What will happen if genes are linked?

Answer 11

Parental allele combinations will be observed at higher frequency than predicted by chance

Question 12

What is complete genetic linkage?

Answer 12

When only parental gametes are formed

Question 13

When is complete genetic linkage observed?

Answer 13

When no crossing over occurs

Question 14

Give an example of organisms that exhibit complete linkage.

Answer 14

Male drosophilas

Question 15

What is the biological basis for complete linkage?

Answer 15

Unknown

Question 16

What is incomplete genetic linkage?

Answer 16

Produces mixture of parental and nonparental gametes

Question 17

How is recombination frequency calculated?

Answer 17

r = # of recombinants / total # of progeny

Question 18

What is recombination frequency most likely a reflection of?

Answer 18

The physical distance between two genes

Question 19

What does it mean if linked genes have higher recombination frequencies?

Answer 19

More distant from one another

Question 20

Explain the experiments conducted by Bateson and Punnett that led to the discovery of genetic linkage.

Answer 20

Crossed pure-breeding purple-flowered, long-pollen plants to red-flowered, round-pollen plants; the purple, long-pollen F1 were interbred to produce F2

Question 21

What were the observed results of Bateson and Punnett’s experiments?

Answer 21

The expected 9 : 3 : 3 :1 ratio was not observed
In F2 progeny, the purple-flowered, long-pollen plants and red-flowered, round pollen plants were seen in larger proportion than expected
These were the same phenotypes of the P generation

Question 22

What did Bateson and Punnett conclude?

Answer 22

An unknown mechanism kept the two parental gamete combinations together, which they called coupling
They described the appearance of the nonparental types as repulsion of the parental alleles.

Question 23

Explain Morgan’s crosses that examined genetic linkage

Answer 23

Crossed pure-breeding white-eyed females with minaiture wings to males wild type for both traits
F1 were wild-type females and white, miniature males
F1 were interbred with a 1:1:1:1 ratio expected

Question 24

What did Morgan see in his F1 crosses?

Answer 24

Many more parental types than recombinant types

Question 25

How did Morgan interpret the results of his crossed?

Answer 25

Nonparental allele combinations resulted from recombination between the X chromosomes of the heterozygous female parent

Question 26

What are the important conclusions from all of Morgan’s crosses?

Answer 26

Genetic linkage is a physical relationship among genes located near one another on a chromosome
Recombination occurs among linked genes less than 50% of the time, and greater than 50% of the gametes contain parental allele combinations
Recombination frequency varies among linked genes in proportion to the distance between them

Question 27

Who created the first genetic linkage map, of five X-linked genes in Drosophila?

Answer 27

Morgan’s student, Alfred Sturtevant

Question 28

What is a map unit

Answer 28

AKA centiMorgan (cM, = 1% RF_