Question 1

Why did Thomas Morgan choose Drosophila melanogaster (fruit flies) as a model organism for studying inheritance patterns?

Accepted Answer

It reproduces quickly, produces hundreds of offspring, and is easy to culture in large numbers for statistical analysis.

Question 2

A female with genotype $$X^C X^c$$ for a sex-linked recessive trait is best described as:

Accepted Answer

A carrier who does not show the trait herself but could pass the allele to offspring.

Question 3

Which of the following best explains why calico cats are almost always female?

Accepted Answer

One X chromosome is randomly inactivated early in development in each cell, so cells descended from that cell only express genes from the remaining active X.

Question 4

Linked genes are genes that:

Accepted Answer

Are located close together on the same chromosome and tend to be inherited together because they're less likely to be separated by crossing over.

Question 5

On a genetic linkage map, if two genes show a 15% recombination frequency, how far apart are they placed on the map?

Accepted Answer

$$15$$ map units (MU)

Question 6

Nondisjunction, where homologous chromosomes fail to separate correctly, can result in which condition?

Accepted Answer

Aneuploidy, where a cell has an abnormal number of specific individual chromosomes (monosomy or trisomy).

Question 7

Polyploidy differs from aneuploidy in that polyploidy involves:

Accepted Answer

Cells carrying two or more complete extra sets of chromosomes.

Question 8

Which of the following is a classic example of an X-linked recessive disorder in humans?

Accepted Answer

Hemophilia

Question 9

A male with genotype $$X^c Y$$ for a sex-linked recessive trait will:

Accepted Answer

Be affected and will pass on the trait to all daughters.

Question 10

Which of the following best describes genomic imprinting?

Accepted Answer

Certain genes are expressed or silenced depending on whether they were inherited from the mother or the father.

Question 11

Mitochondrial DNA is typically inherited through which parent?

Accepted Answer

Only the mother, since the egg (ovum) contributes the organelles.

Question 12

Why is the Y chromosome useful for tracing paternal lineage over many generations?

Accepted Answer

Because it is passed from father to son largely without recombination, so mutations accumulate and persist along a single paternal line.

Question 13

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

Accepted Answer

Nondisjunction resulting in trisomy 21.

Question 14

A pedigree shows a trait that appears only in males and is passed from father to all sons. This pattern is most likely due to:

Accepted Answer

A Y-linked gene.

Question 15

If a woman who is a carrier for red-green color blindness (X-linked recessive) has children with a man with normal vision, what is the probability that their son will be color blind?

Accepted Answer

$$0.25$$

Question 16

Which of the following best describes the difference between parental and recombinant chromosome types?

Accepted Answer

Recombinant types have new combinations of alleles due to crossing over during meiosis.

Question 17

A geneticist observes that two genes in fruit flies have a recombination frequency of $$37\%. $$How many map units apart are these genes?

Accepted Answer

$$37$$ map units

Question 18

Which syndrome is caused by a deletion in the short arm of chromosome 5 and is characterized by intellectual disability and a cat-like cry?

Accepted Answer

Cri du chat syndrome

Question 19

Which of the following is a real-world application of mitochondrial DNA analysis?

Accepted Answer

Tracing maternal ancestry and migration patterns over thousands of years.

Question 20

A cultivated strawberry plant is octoploid ($$8N$$), while a wild strawberry is diploid ($$2N). $$What does this difference illustrate?

Accepted Answer

Polyploidy

Chapter 15: The Chromosomal Basis of Inheritance – Study Notes

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