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 is expected if the genes are unlinked?

Accepted Answer

$$1:1:1:1$$

Question 3

A researcher crosses two true-breeding blind fish strains and observes that the offspring can see. What does this result indicate about the mutations in the two strains?

Accepted Answer

The mutations are in different genes.

Question 4

Given the following complementation table for five blind fish strains (#4–#8), how many different genes are minimally required for sight?

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

Accepted Answer

3

Question 5

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

Accepted Answer

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

Question 6

Which scenario would most likely result in Mendelian ratios being modified in a dihybrid cross?

Accepted Answer

The two genes are located close together on the same chromosome and are linked.

Question 7

In Drosophila, the wild-type allele is indicated by '+'. If a fly has the genotype $$pr^+ pr \, vg^+ vg$$, what is its phenotype?

Accepted Answer

Red eyes, full-size wings

Question 8

A test cross between $$pr^+ pr \, vg^+ vg (F1) $$and $$pr \, vg ($$double mutant) yields the following progeny: 133 red eyes/full wings, 154 purple eyes/full wings, 151 red eyes/vestigial wings, 119 purple eyes/vestigial wings. What is the recombination frequency ($$r) $$between the pr and vg genes?

Use the formula:

$$ r = \frac{	ext{number of recombinants}}{	ext{total number of progeny}} 	imes 100 $$

Accepted Answer

$$r = 11.5\%$$

Question 9

If two genes are very close together on the same chromosome, what is the expected frequency of recombinant gametes compared to parental gametes?

Accepted Answer

Recombinant gametes will be much less frequent than parental gametes.

Question 10

Which statistical test is most appropriate to determine if observed dihybrid test cross ratios deviate significantly from the expected $$1:1:1:1$$ ratio due to genetic linkage?

Accepted Answer

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

Question 11

In a dihybrid test cross, the observed progeny numbers are: 270, 278, 225, and 227. What is the expected number for each phenotype if the genes assort independently and the total progeny is 1000?

Accepted Answer

$$250$$

Question 12

Which of the following is the correct formula for calculating the chi-square ($$\$$chi^2$$) statistic in a genetic cross?

Accepted Answer

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

Question 13

If the calculated $$\$$chi^2$$ value for a test cross is much greater than the critical value at p=0.05$, what conclusion should be drawn?

Accepted Answer

Reject the null hypothesis; genes are likely linked.

Question 14

Which of the following best describes syntenic genes?

Accepted Answer

Genes located on the same chromosome.

Question 15

A pedigree shows segregation of two linked disorders: one autosomal dominant (A = disease, a = healthy) and one autosomal recessive (b = disease, B = healthy). If individual II-1 received the gamete 'Ab' from II-2, is this gamete parental or non-parental?

Accepted Answer

Parental, if the original parental chromosomes were 'Ab' and 'aB'.

Question 16

Why does recombination frequency provide information about the physical distance between two genes on a chromosome?

Accepted Answer

Because recombination occurs more frequently between genes that are farther apart.

Question 17

In a test cross involving linked genes, which gamete types are expected to be most frequent?

Accepted Answer

Parental gametes

Question 18

Which of the following crosses would you use to determine if two genes are genetically linked?

Accepted Answer

Perform a test cross between a dihybrid and a double recessive individual.

Question 19

If two genes are unlinked, what is the maximum recombination frequency that can be observed?

Accepted Answer

$$50\%$$

Question 20

Which of the following is a real-world application of genetic linkage analysis?

Accepted Answer

Mapping disease genes in human pedigrees.

Genetic Linkage, Complementation, and Deviations from Mendelian Ratios

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