Question 1

Why is genetic mapping still used to find mutants instead of relying solely on genetic sequencing?

Accepted Answer

Genetic mapping allows researchers to pinpoint the location of a gene influencing a trait or disease before the gene is sequenced, especially when the causative mutation is unknown.

Question 2

What is a single nucleotide polymorphism (SNP) and how is it used in genetic mapping?

Accepted Answer

A SNP is a single base pair change in the DNA sequence, often in noncoding regions, and is used as a genetic marker to track inheritance patterns.

Question 3

Given the following haplotype frequencies in a population: 60% AB, 10% aB, 10% Ab, 20% ab, calculate the coefficient of linkage disequilibrium (D).

Accepted Answer

$$D = 0.11$$

Question 4

Which of the following best describes a haplotype?

Accepted Answer

A haplotype is a specific array of SNPs in a small region on a single chromosome that tend to be inherited together.

Question 5

A LOD score of 3.5 is calculated for two genes in a pedigree. What does this indicate?

Accepted Answer

There is significant evidence in favor of genetic linkage between the two genes.

Question 6

In a test cross, the following progeny numbers are observed: 899 (+ e +), 876 (c + k), 67 (+ e k), 58 (c + +), 49 (+ + k), 44 (c e +), 4 (+ + +), 3 (c e k). What is the recombination frequency between the e and k loci?

Accepted Answer

$$6.6\%$$

Question 7

Which scenario would most likely result in linkage disequilibrium in a population?

Accepted Answer

Introduction of new haplotypes through migration or a new mutation closely linked to an existing allele.

Question 8

If the recombination rate ($$r) $$between two loci is 0.2 and the current linkage disequilibrium coefficient ($$D) is 0.11$$, what will the new $$D$$ value be in the next generation?

Accepted Answer

$$D = 0.088$$

Question 9

Which of the following statements about genome-wide association studies (GWAS) is correct?

Accepted Answer

GWAS compares SNP frequencies between cases and controls to identify associations with traits or diseases.

Question 10

What does a Manhattan plot represent in the context of GWAS?

Accepted Answer

It indicates the strength of association between SNPs and traits across the genome, with higher bars representing stronger associations.

Question 11

Which of the following best explains why physical distance and recombination distance are not always equivalent?

Accepted Answer

Recombination hotspots and coldspots can cause the genetic map to stretch or contract relative to the physical map.

Question 12

If two genes have a recombination frequency of 50%, what can you conclude about their genetic relationship?

Accepted Answer

They are unlinked and assort independently.

Question 13

Which of the following is a possible cause of linkage disequilibrium in a population?

Accepted Answer

Natural selection favoring a new beneficial mutation closely linked to other alleles (genetic hitchhiking).

Question 14

In a three-point test cross, why is the least abundant class of offspring important?

Accepted Answer

It identifies the gene in the middle of the three, as these are double recombinants.

Question 15

Which of the following equations correctly calculates the recombination frequency ($$r) $$between two genes?

Accepted Answer

$$r = \frac{	ext{number of recombinants}}{	ext{total number of progeny}}$$

Question 16

What is the effect of recombination on linkage disequilibrium over evolutionary time?

Accepted Answer

Recombination breaks down linkage disequilibrium, causing alleles to assort more independently.

Question 17

Which of the following best describes genetic hitchhiking?

Accepted Answer

A neutral or deleterious allele increases in frequency because it is closely linked to a beneficial allele under selection.

Question 18

If a population is in linkage equilibrium, what is true about the haplotype frequencies?

Accepted Answer

The frequency of a haplotype equals the product of the frequencies of its component alleles.

Gene Linkage, Recombination, and Genetic Mapping: Study Notes for Genetics Students

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