Question 1

Which experimental technique allows scientists to determine the physical location of a specific gene on a chromosome by using fluorescent probes?

Accepted Answer

Fluorescence In Situ Hybridization (FISH)

Question 2

In Drosophila melanogaster, the gene for white eyes is located on the X chromosome. If a white-eyed male (XwY) is crossed with a wild-type red-eyed female (X+X+), what will be the eye color of the F1 generation females?

Accepted Answer

All will have red eyes

Question 3

Which of the following best explains why males are more frequently affected by X-linked recessive disorders such as hemophilia and color blindness?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will cause the disorder.

Question 4

A woman who is heterozygous for the X-linked color blindness allele (X	extsuperscript{N}X	extsuperscript{c}) and a man with normal vision (X	extsuperscript{N}Y) have a son. What is the probability that their son will be color blind?

Accepted Answer

$$\frac{1}{2}$$

Question 5

Which of the following is a direct consequence of X-inactivation in female mammals?

Accepted Answer

Females are mosaics for X-linked traits, such as the tortoiseshell pattern in cats.

Question 6

In a testcross between AaBb (heterozygote for two linked genes) and aabb, the following progeny are observed: 38% AB, 38% ab, 12% Ab, and 12% aB. What is the recombination frequency between the two genes?

Accepted Answer

$$24\%$$

Question 7

Which chromosomal abnormality is responsible for Down syndrome?

Accepted Answer

Trisomy of chromosome 21

Question 8

A male with Klinefelter syndrome has the karyotype XXY. Which of the following meiotic errors could produce this condition?

Accepted Answer

Nondisjunction at meiosis I in the mother

Question 9

If two genes are located very close together on the same chromosome, which of the following is most likely to occur?

Accepted Answer

They will be inherited together more frequently than genes that are far apart.

Question 10

Which formula is used to calculate the chi-square statistic for testing genetic hypotheses?

Accepted Answer

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

Question 11

In birds, sex is determined by the Z-W system. Which statement is correct regarding the sex chromosomes in birds?

Accepted Answer

Females are ZW and males are ZZ.

Question 12

A genetic map is constructed using recombination frequencies. If two genes have a recombination frequency of 1%, how many map units apart are they?

Accepted Answer

$$1$$ map unit

Question 13

Which of the following is true about the haplo-diploid system of sex determination found in bees?

Accepted Answer

Females develop from fertilized diploid eggs, males from unfertilized haploid eggs.

Question 14

A woman who is a carrier for hemophilia (X	extsuperscript{H}X	extsuperscript{h}) marries a man without hemophilia (X	extsuperscript{H}Y). What is the probability that their daughter will be a carrier?

Accepted Answer

$$\frac{1}{2}$$

Question 15

Which of the following statements about nondisjunction is correct?

Accepted Answer

It can occur during either meiosis I or meiosis II.

Question 16

A pedigree shows that a rare mutant trait is present in every generation and affects both males and females equally. What is the most likely mode of inheritance?

Accepted Answer

Autosomal dominant

Question 17

Which of the following is NOT a feature of genetic linkage?

Accepted Answer

Linked genes always show independent assortment.

Question 18

In a cross between two heterozygotes for two genes (AaBb x AaBb), if the genes are unlinked, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:3:1$$

Question 19

Which of the following is a real-world example of X-inactivation leading to a visible phenotype?

Accepted Answer

Tortoiseshell coat pattern in female cats

Question 20

A woman with congenital cataracts (autosomal dominant) marries a man without cataracts. Two of their four children, a boy and a girl, develop cataracts. What is the probability that their next child will be a girl with cataracts?

Accepted Answer

$$\frac{1}{4}$$

Genetics Part 3 Study Guide: Chromosomal Basis of Inheritance and Genetic Linkage

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