Question 1

Which of the following best describes the relationship between recombination frequency and the physical distance between two genes on a chromosome?

Accepted Answer

Recombination frequency increases as the physical distance between genes increases.

Question 2

A geneticist observes that two genes in Drosophila produce 10% recombinant offspring in a test cross. What is the genetic distance between these genes?

Accepted Answer

$$10\ 	ext{cM}$$

Question 3

Which of the following statements about complete genetic linkage is correct?

Accepted Answer

Complete genetic linkage results in only parental gametes.

Question 4

In a dihybrid test cross, the following progeny numbers are observed: 400 parental type 1, 400 parental type 2, 100 recombinant type 1, and 100 recombinant type 2. What is the recombination frequency ($$r$$)?

Accepted Answer

$$r = \frac{100 + 100}{400 + 400 + 100 + 100} = 0.2$$

Question 5

Which experimental result would most strongly suggest that two genes are linked?

Accepted Answer

The observed ratio of parental to recombinant phenotypes is significantly greater than 1:1.

Question 6

Which of the following is a correct interpretation of a lod score of 3.5 for two genes in a human pedigree?

Accepted Answer

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

Question 7

Which of the following best explains why recombination rates can differ between males and females in many species?

Accepted Answer

The heterogametic sex generally has a lower recombination rate than the homogametic sex.

Question 8

A researcher is mapping human genes using VNTRs, SNPs, and RFLPs. What do these markers have in common?

Accepted Answer

They are all types of genetic markers found in noncoding regions of the genome.

Question 9

Which of the following scenarios would most likely result in linkage disequilibrium in a population?

Accepted Answer

Migration introducing new haplotypes into the population.

Question 10

In a GWAS (Genome-Wide Association Study), what does a high green bar on a Manhattan plot indicate?

Accepted Answer

A strong association between a genetic marker and a trait or condition.

Question 11

Which of the following is the best definition of a haplotype?

Accepted Answer

A specific array of SNPs in a small region on a single chromosome.

Question 12

Why are X-linked genes generally easier to map in humans than autosomal genes?

Accepted Answer

X-linked genes show distinct inheritance patterns and are hemizygous in males.

Question 13

A cross between two plants produces the following F2 progeny: 4831 purple, long; 390 purple, round; 393 red, long; 1338 red, round. What does this deviation from the expected 9:3:3:1 ratio suggest?

Accepted Answer

The two genes are genetically linked.

Question 14

Which of the following is a direct cytological method for demonstrating that recombination is associated with crossing over?

Accepted Answer

Tracking structural chromosome markers during meiosis, as done by Creighton and McClintock.

Question 15

If two genes are 50 map units apart, what is the expected recombination frequency between them?

Accepted Answer

$$50\%$$

Question 16

Which of the following factors does NOT influence recombination frequency?

Accepted Answer

The number of chromosomes in the cell.

Question 17

A disease-causing allele is found to segregate with a known SNP marker in a family pedigree. What does this allow researchers to determine?

Accepted Answer

The allelic phase of the disease-causing gene.

Question 18

Which of the following best describes the outcome of a chi-square test in genetic linkage analysis?

Accepted Answer

It determines whether the observed progeny ratios significantly deviate from those expected under independent assortment.

Question 19

Which of the following is a plausible reason why recombination rates might increase in populations undergoing artificial selection?

Accepted Answer

Recombination increases genetic diversity, which can be favored by selection.

Question 20

Which of the following is true about linkage groups in the context of human gene mapping?

Accepted Answer

They are clusters of syntenic genes that are linked to one another.

Genetic Linkage and Mapping in Eukaryotes – Study Notes

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