Gene Mapping

Question 1

What is a gene map?

Answer 1

A gene map shows the relative order of genes on the chromosome and the distance between the genes.

Question 2

Why are gene maps useful?

Answer 2

• Identify genes linked to diseases or traits (positional cloning)
• Aid in studying gene function
• Support plant/animal breeding programs
• Compare genome structures across species (conserved/shared synteny)

Question 3

What is the approximate conversion of 1 centiMorgan (cM) in humans?

Answer 3

1 cM is approximately 1 Mb (megabase) in humans.

Question 4

Name the three types of gene maps.

Answer 4

• Genetic/Linkage map
• Cytogenetic map
• Physical map

Question 5

What is a physical map?

Answer 5

A physical map is created using restriction enzymes that cut DNA at specific sites and provides the DNA sequence of human chromosomes.

Question 6

What is the significance of G-banding in cytogenetic maps?

Answer 6

G-banding involves staining chromosomes to produce a characteristic pattern of light and dark bands, with each band assigned a specific number.

Question 7

What occurs during genetic linkage?

Answer 7

Alleles of genes on the same chromosome will segregate together in gametes during meiosis unless crossing-over occurs between them.

Question 8

What is the relationship between crossing-over frequency and gene distance?

Answer 8

The frequency of crossing-over between two gene loci is proportional to the physical distance between them on the chromosome.

Question 9

What does a recombination frequency (RF) of less than 50% indicate?

Answer 9

Genes are linked on the same chromosome.

Question 10

What is a testcross?

Answer 10

A testcross is designed to determine the genotypes of gametes from one parent based on the phenotypes of the offspring they produce.

Question 11

How is genetic distance calculated in linkage mapping?

Answer 11

Genetic distance is calculated using the formula RF = (number of recombinant progeny x 100) / total number of progeny.

Question 12

What is the unit of measurement for genetic distance?

Answer 12

Map distances are given in centiMorgans (cM).

Question 13

What is the expected percentage of recombinant gametes when genes are on different chromosomes?

Answer 13

50% recombinant gametes.

Question 14

What is the problem with measuring genetic distances over large distances?

Answer 14

Double (or multiple) crossover events can underestimate the true distance between genes.

Question 15

True or False: Map distances are additive over long distances.

Answer 15

False. Map distances are additive over short distances but not over long distances.

Question 16

What is the significance of the frequency of crossing over in linkage mapping?

Answer 16

It gives a measure of the distance between genes.

Question 17

What happens during independent assortment?

Answer 17

Independent assortment produces recombinant gametes from genes on different chromosomes or genes that are far apart on the same chromosome.

Question 18

Fill in the blank: A genetic map shows the _______ order of genes on the chromosome.

Answer 18

[relative]

Question 19

What is the genetic distance if the RF is 10%?

Answer 19

10 cM.

Question 20

In a two-point mapping experiment, what are the parental types?

Answer 20

The parental types are the most frequent offspring phenotypes.

Question 21

What is an example of a genetic trait linked to a gene?

Answer 21

Cystic fibrosis is linked to a mutation in the CFTR gene.

Question 22

How many G-dark bands are visible on the 23 human chromosomes?

Answer 22

About 850 G-dark bands.

Question 23

What is the expected outcome of a testcross with a double heterozygote?

Answer 23

It produces both parental and recombinant gametes.

Question 24

What is the role of positive or negative interference in crossover events?

Answer 24

Interference affects the probability of crossover events in adjacent regions, influencing genetic mapping.