Question 1

Which of the following best explains why Thomas Hunt Morgan chose Drosophila melanogaster for his genetic experiments?

Accepted Answer

They produce many offspring, have a short generation time, and possess only four pairs of chromosomes.

Question 2

In Morgan's experiment with white-eyed and red-eyed fruit flies, why did only males in the F2 generation exhibit the white-eyed phenotype?

Accepted Answer

The white-eyed allele is recessive and located on the X chromosome, so males (XY) only need one copy to express the trait.

Question 3

Which of the following statements about X-linked recessive disorders is correct?

Accepted Answer

Males are more likely to express X-linked recessive disorders because they are hemizygous for the X chromosome.

Question 4

A woman who is heterozygous for an X-linked gene (e.g., color blindness) can be described as a mosaic for that character. What is the molecular basis for this phenomenon?

Accepted Answer

One X chromosome is randomly inactivated in each cell during embryonic development, forming a Barr body.

Question 5

Which chromosomal alteration is correctly matched with its description?

Accepted Answer

Translocation: Moves a segment from one chromosome to a nonhomologous chromosome.

Question 6

A geneticist observes a 17% recombination frequency between two genes in Drosophila. What does this indicate about the genes' locations?

Accepted Answer

The genes are on the same chromosome and are 17 map units apart.

Question 7

Which of the following best describes the chromosomal basis for Mendel’s law of independent assortment?

Accepted Answer

Homologous chromosomes separate during meiosis I, and nonhomologous chromosomes assort independently.

Question 8

A child is born with Down syndrome. Which chromosomal event most likely caused this condition?

Accepted Answer

Nondisjunction leading to trisomy 21.

Question 9

Which of the following is true about polyploidy in plants?

Accepted Answer

Polyploid plants often appear more normal than aneuploid plants.

Question 10

A male with Klinefelter syndrome has the genotype XXY. Which meiotic error most likely led to this condition?

Accepted Answer

Nondisjunction of homologous chromosomes during meiosis I in the mother or father.

Question 11

Which of the following best explains why mitochondrial disorders are inherited maternally?

Accepted Answer

The zygote’s cytoplasm, including mitochondria, comes from the egg.

Question 12

A plant with variegated leaves (green and white patches) is crossed with a plant with all green leaves. All offspring have variegated leaves. What is the most likely explanation?

Accepted Answer

The trait is controlled by a gene in the chloroplast DNA, which is inherited maternally.

Question 13

Which of the following is an example of genomic imprinting?

Accepted Answer

A gene is expressed only if inherited from the father, as in the case of the mouse Igf2 gene.

Question 14

If a crossover occurs between two linked genes during meiosis, what is the expected result in the gametes?

Accepted Answer

Some gametes will have recombinant combinations of alleles.

Question 15

A testcross between a dihybrid fruit fly (b+ vg+/b vg) and a double mutant (b vg/b vg) produces mostly parental-type offspring and some recombinant offspring. What does this indicate about the genes?

Accepted Answer

The genes are linked but crossing over can occur between them.

Question 16

Which equation correctly represents the calculation of recombination frequency between two genes?

Accepted Answer

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

Question 17

Which of the following best describes the effect of crossing over on genetic variation?

Accepted Answer

Crossing over increases genetic variation by producing recombinant chromosomes.

Question 18

A child is diagnosed with chronic myelogenous leukemia (CML). Which chromosomal event is most closely associated with this disease?

Accepted Answer

A reciprocal translocation between chromosomes 9 and 22.

Question 19

Which of the following is a correct statement about aneuploidy?

Accepted Answer

Aneuploidy refers to an abnormal number of a particular chromosome, such as trisomy 21.

Chapter 15: The Chromosomal Basis of Inheritance – Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard