Q: A geneticist observes the following progeny from a test cross: 1239 red eyes, normal wings; 1095 red eyes, short wings; 250 purple eyes, normal wings; 252 purple eyes, short wings. What is the recombination frequency between the eye color and wing genes?

$$\frac{250+252}{1239+1095+250+252} \times 100 = 17.7\%$$

Q: What is the formula for calculating genetic map distance in centimorgans (cM) using Sturtevant's method?

$$\text{cM} = \frac{\text{Number of recombinants}}{\text{Total progeny}} \times 100$$

Q: In a mapping experiment, the sum of recombinants is 44 and the total progeny is 400. What is the genetic map distance between the two loci?

$$\frac{44}{400} \times 100 = 11.0\ \text{cM}$$

Question 1

In a dihybrid cross between Drosophila with genotype $$PrPr	ext{ VgVg} ($$red eyes, normal wings) and $$prpr	ext{ vgvg} ($$purple eyes, vestigial wings), what is the expected phenotypic ratio in the F2 generation if the genes assort independently?

Accepted Answer

9:3:3:1

Question 2

If two genes are located 1 centimorgan (cM) apart on a chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$1\%$$

Question 3

A geneticist observes the following progeny from a test cross: 1239 red eyes, normal wings; 1095 red eyes, short wings; 250 purple eyes, normal wings; 252 purple eyes, short wings. What is the recombination frequency between the eye color and wing genes?

Accepted Answer

$$\frac{250+252}{1239+1095+250+252} 	imes 100 = 17.7\%$$

Question 4

Which of the following best describes linkage disequilibrium?

Accepted Answer

Non-random association of alleles at different loci in a population

Question 5

If two genes are linked and 10 cM apart, what is the probability that alleles will be inherited together?

Accepted Answer

$$90\%$$

Question 6

Which experimental design is best for identifying the inheritance pattern of a rare genetic disease in a family?

Accepted Answer

Pedigree analysis

Question 7

A researcher uses microsatellite markers to map a disease locus. What is the main advantage of using these markers?

Accepted Answer

They detect genetic variation in repeat length at specific loci

Question 8

In a pedigree analysis, a dominant trait is observed to co-segregate with marker M5 in all affected individuals. What does this suggest?

Accepted Answer

Trait is linked to M5 allele

Question 9

Which of the following is NOT a limitation of cross-sectional studies in human genetics?

Accepted Answer

They account for differing histories among individuals

Question 10

What is the formula for calculating genetic map distance in centimorgans (cM) using Sturtevant's method?

Accepted Answer

$$	ext{cM} = \frac{	ext{Number of recombinants}}{	ext{Total progeny}} 	imes 100$$

Question 11

If two genes are unlinked, what is the expected ratio of parental to recombinant phenotypes in a test cross?

Accepted Answer

1:1

Question 12

Which type of genetic marker is based on variation at a single nucleotide position?

Accepted Answer

Single Nucleotide Polymorphism (SNP)

Question 13

A disease gene is mapped to a region with high linkage disequilibrium. What does this imply about the alleles in this region?

Accepted Answer

Alleles are inherited together more often than expected by chance

Question 14

In a mapping experiment, the sum of recombinants is 44 and the total progeny is 400. What is the genetic map distance between the two loci?

Accepted Answer

$$\frac{44}{400} 	imes 100 = 11.0\ 	ext{cM}$$

Question 15

Which of the following is an example of a polymorphism?

Accepted Answer

Heterozygous sequence AB

Question 16

Why are pedigrees useful in genetic studies?

Accepted Answer

They help determine inheritance patterns and probability of inheriting a disease

Question 17

If two genes are 50 cM apart, what is the expected ratio of parental to recombinant phenotypes?

Accepted Answer

1:1

Question 18

Which of the following is a limitation of randomized controlled trials in genetic studies?

Accepted Answer

They are expensive and require large enough numbers

Question 19

A researcher finds that two genes are inherited together 99% of the time. What does this suggest about their physical location?

Accepted Answer

They are very close together on the same chromosome

Question 20

Which method is best for identifying the physical location of a mutation in the genome?

Accepted Answer

Use of polymorphisms and linkage disequilibrium/recombination

Genetic Linkage, Mapping, and Human Disease: Study Notes

Study Guide - Practice Questions

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