Q: Given the following progeny counts from a three-factor cross: 800 parental, 150 single crossover, 50 double crossover. What is the coefficient of coincidence ($$C) if $$the expected double crossover frequency is $$0.02$$ and the total number of progeny is $$1000$$?

$$C = \frac{50}{0.02 \times 1000} = 2.5$$

Q: In Neurospora, how is the distance between a gene and the centromere calculated using asci types?

Distance (in cM) $$= \frac{1}{2} \times \frac{\text{Number of second division segregation asci}}{\text{Total number of asci}} \times 100$$

Question 1

Which of the following best describes the concept of gene linkage?

Accepted Answer

Two genes are located close together on the same chromosome and tend to be inherited together.

Question 2

If two genes are syntenic, which of the following statements is true?

Accepted Answer

They are located on the same chromosome, but may or may not be linked depending on their distance.

Question 3

A species has 8 chromosomes in its somatic cells. How many linkage groups would you expect in this species?

Accepted Answer

8

Question 4

The frequency of recombination between two genes is measured in which units?

Accepted Answer

Centimorgans (cM)

Question 5

If two genes are 10 cM apart, what is the expected proportion of recombinant gametes produced?

Accepted Answer

$$0.10$$

Question 6

Why is a testcross used to measure map distances between genes?

Accepted Answer

It allows the detection of recombination events by producing progeny with distinguishable phenotypes.

Question 7

In linkage notation, what does the coupling (cis) conformation indicate?

Accepted Answer

Both dominant alleles are on the same chromosome and both recessive alleles are on the homologous chromosome.

Question 8

In a two-factor linkage analysis, if the two loci are linked, which progeny would be more abundant?

Accepted Answer

Progeny resulting from non-recombination (parental types).

Question 9

In a three-factor linkage analysis, which progeny would have the lowest frequency if the three loci are linked?

Accepted Answer

Double crossover progeny.

Question 10

Given the following progeny counts from a three-factor cross: 800 parental, 150 single crossover, 50 double crossover. What is the coefficient of coincidence ($$C) if $$the expected double crossover frequency is $$0.02$$ and the total number of progeny is $$1000$$?

Accepted Answer

$$C = \frac{50}{0.02 	imes 1000} = 2.5$$

Question 11

Which of the following best explains why genetic map distances are often underestimated?

Accepted Answer

Multiple crossovers between loci can restore parental combinations, making recombination events undetectable.

Question 12

Which technique is used to detect DNA sequence differences between individuals using restriction enzymes and gel electrophoresis?

Accepted Answer

RFLP analysis

Question 13

Which enzyme is used to amplify DNA during PCR?

Accepted Answer

Taq polymerase

Question 14

Which of the following statements about RFLP markers is correct?

Accepted Answer

RFLP markers are inherited in a co-dominant manner.

Question 15

Which method is NOT used for physical mapping of genes to chromosomes?

Accepted Answer

PCR amplification

Question 16

In Neurospora, how is the distance between a gene and the centromere calculated using asci types?

Accepted Answer

Distance (in cM) $$= \frac{1}{2} 	imes \frac{	ext{Number of second division segregation asci}}{	ext{Total number of asci}} 	imes 100$$

Question 17

Which type of ascus indicates that recombination has occurred between a gene and the centromere?

Accepted Answer

Second division segregation ascus

Question 18

What is gene conversion, and in which organisms is it most easily identified?

Accepted Answer

Gene conversion is a non-reciprocal transfer of genetic information, easily identified in fungi producing tetrads or octads.

Question 19

If two mutants show the same abnormal phenotype, which experiment would you use to determine if the mutations are in the same gene?

Accepted Answer

A complementation test

Question 20

In a complementation test, if two mutants fail to complement each other, what does this indicate?

Accepted Answer

The mutations are in the same gene (same complementation group).

Genetics Exam 3 Review – Step-by-Step Study Guidance

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