Q: In gene mapping, how is recombination frequency ($$RF) $$calculated from a two-point test cross?

$$RF = \frac{\text{Number of recombinant offspring}}{\text{Total number of offspring}} \times 100$$

Question 1

A researcher performs a dihybrid cross and observes the following phenotypic ratio: 9:3:3:1. Which null hypothesis should be stated for a chi-square test analyzing these results?

Accepted Answer

The observed ratio fits Mendelian independent assortment.

Question 2

In a chi-square test, what does a p-value represent?

Accepted Answer

The probability that the observed data occurred by chance under the null hypothesis.

Question 3

Given the following observed values from a dihybrid cross: 90, 30, 30, 10. The expected ratio is 9:3:3:1. What is the formula for the chi-square statistic?

Accepted Answer

$$\sum \frac{(O - E)^2$}{E}$$

Question 4

In gene mapping, how is recombination frequency ($$RF) $$calculated from a two-point test cross?

Accepted Answer

$$RF = \frac{	ext{Number of recombinant offspring}}{	ext{Total number of offspring}} 	imes 100$$

Question 5

A three-point test cross yields the following recombinant classes: single crossovers between A-B, single crossovers between B-C, and double crossovers. What is the first step to determine gene order?

Accepted Answer

Identify the double crossover class.

Question 6

Which of the following best describes a double crossover recombinant?

Accepted Answer

An offspring with two recombination events between three genes.

Question 7

What is interference in gene mapping?

Accepted Answer

The phenomenon where one crossover decreases the likelihood of another nearby crossover.

Question 8

Which of the following statements about recombination hotspots is correct?

Accepted Answer

They are regions where recombination occurs more frequently.

Question 9

A human with an XY karyotype but a deletion of the SRY region would most likely:

Accepted Answer

Develop as a typical female.

Question 10

Which region of the Y chromosome is responsible for pairing with the X chromosome during meiosis?

Accepted Answer

PAR region

Question 11

What is the molecular explanation for complete dominance?

Accepted Answer

The dominant allele produces enough functional protein to mask the effect of the recessive allele.

Question 12

A cross between two heterozygotes for a dominant lethal allele results in which progeny ratio?

Accepted Answer

2:1 (heterozygote: homozygous recessive)

Question 13

Which of the following best describes codominance?

Accepted Answer

Both alleles are expressed equally in the phenotype.

Question 14

A pedigree shows that all children of an affected mother are affected, but none of the children of an affected father are affected. What type of inheritance is most likely?

Accepted Answer

Mitochondrial inheritance

Question 15

What is heteroplasmy?

Accepted Answer

The presence of multiple types of mitochondrial DNA within a cell.

Question 16

Which of the following is NOT a characteristic of mtDNA?

Accepted Answer

It undergoes recombination during meiosis.

Question 17

In maternal effect inheritance, whose genotype determines the offspring's phenotype?

Accepted Answer

The mother's genotype.

Question 18

Which of the following best describes a Barr body?

Accepted Answer

An inactivated X chromosome found in female cells.

Question 19

A woman with a mutation in her mtDNA has three children. What is the probability that all three children inherit the mutation, assuming random segregation of mitochondria and heteroplasmy?

Accepted Answer

It depends on the proportion of mutant mitochondria in the egg cells.

Question 20

Which of the following is a limitation of gene mapping in humans?

Accepted Answer

Controlled crosses cannot be performed.

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