Q: A geneticist observes the following offspring from a test cross: 133 red eyes/full wings, 154 purple eyes/full wings, 151 red eyes/vestigial wings, and 119 purple eyes/vestigial wings. Which formula should be used to calculate the recombination frequency ($$r) $$between the two genes?

$$r = \frac{\text{number of recombinant offspring}}{\text{total number of offspring}} \times 100$$

Question 1

Which statement best explains why linked genes violate Mendel's law of independent assortment?

Accepted Answer

Linked genes are located close together on the same chromosome, so their alleles tend to be inherited together.

Question 2

In a test cross between a dihybrid plant (LlIi) and a double recessive plant (llii), what phenotypic ratio would you expect if the genes for height and pod shape are unlinked?

Accepted Answer

$$1:1:1:1$$

Question 3

A geneticist observes the following offspring from a test cross: 133 red eyes/full wings, 154 purple eyes/full wings, 151 red eyes/vestigial wings, and 119 purple eyes/vestigial wings. Which formula should be used to calculate the recombination frequency ($$r) $$between the two genes?

Accepted Answer

$$r = \frac{	ext{number of recombinant offspring}}{	ext{total number of offspring}} 	imes 100$$

Question 4

If two genes are located very close together on the same chromosome, what is the expected recombination frequency between them?

Accepted Answer

Close to 0%

Question 5

Which statistical test is most appropriate for determining whether the observed offspring ratios in a genetic cross deviate significantly from the expected Mendelian ratio?

Accepted Answer

Chi-square ($$\$$chi^2$$) test

Question 6

In a complementation test, two mutant strains of blind fish are crossed and the offspring all have sight. What does this result indicate?

Accepted Answer

The mutations are in different genes.

Question 7

Given the following complementation table for five blind fish strains (#4 to #8), how many different genes are responsible for sight? (Each '-' indicates non-complementation, each '+' indicates complementation)

#4 #5 #6 #7 #8
#4 - - + + +
#5 - - + + +
#6 + + - + -
#7 + + + - +
#8 + + - + -

Accepted Answer

3

Question 8

Which of the following best describes syntenic genes?

Accepted Answer

Genes located on the same chromosome.

Question 9

A test cross between a dihybrid fly (pr+ vg+) and a double mutant (pr vg) yields mostly parental phenotypes and few recombinants. What does this suggest about the physical distance between the pr and vg genes?

Accepted Answer

They are close together on the same chromosome.

Question 10

If the recombination frequency between two genes is 20%, what is the genetic map distance between them?

Accepted Answer

$$20$$ centimorgans (cM)$

Question 11

In a pedigree showing segregation of two linked disorders, one autosomal dominant (A) and one autosomal recessive (b), how can you determine if a gamete received is parental or non-parental?

Accepted Answer

By comparing the arrangement of alleles in the gamete to the parental chromosome arrangement.

Question 12

Which of the following would most likely result in a deviation from the expected $$1:1:1:1$$ ratio in a test cross of a dihybrid organism?

Accepted Answer

Genes are linked and close together on the same chromosome.

Question 13

If the observed offspring numbers in a test cross are: 270, 278, 225, and 227, and the expected numbers are all 250, what is the chi-square ($$\$$chi^2$$) value for this cross?

Accepted Answer

$$\$$chi^2$$ = 93$$

Question 14

Which of the following is true about recombinant gametes?

Accepted Answer

They result from crossing over between homologous chromosomes.

Question 15

Why are parental combinations more common than recombinant combinations when two genes are linked?

Accepted Answer

Because linked genes are inherited together unless a recombination event occurs between them.

Question 16

Which of the following would NOT affect Mendelian ratios in a genetic cross?

Accepted Answer

Genes located on different chromosomes assorting independently.

Question 17

In Drosophila, the wild-type allele is indicated by which symbol?

Accepted Answer

'+'

Question 18

Which of the following is the correct null hypothesis for a chi-square test in a genetic linkage experiment?

Accepted Answer

The ratio of offspring is consistent with independent assortment.

Question 19

If two genes are unlinked, what proportion of recombinant gametes would you expect in a test cross?

Accepted Answer

$$50\%$$

Question 20

Which of the following best describes a 'complementation group' in genetics?

Accepted Answer

A group of mutations that do not complement each other and are in the same gene.

Genetic Linkage, Complementation, and Deviations from Mendelian Ratios

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