Question 1

Which of the following best describes the difference between euploidy and aneuploidy?

Accepted Answer

Euploidy refers to variation in the number of complete sets of chromosomes, while aneuploidy refers to variation in the number of particular chromosomes within a set.

Question 2

A cytogeneticist is examining a karyotype and notices a chromosome with the centromere very close to one end, resulting in a very short p arm and a long q arm. How would this chromosome be classified?

Accepted Answer

Acrocentric

Question 3

Which of the following statements about G-banding is correct?

Accepted Answer

G-banding uses the dye Giemsa to produce unique banding patterns that distinguish individual chromosomes.

Question 4

A human cell is found to have three copies of chromosome 21. What is the term for this condition, and what is the expected percentage of gene product for chromosome 21?

Accepted Answer

Trisomy; 150\% gene product

Question 5

Which equation correctly represents the chromosome number in a triploid fruit fly, given that the diploid number is $$2n$$?

Accepted Answer

$$3n$$

Question 6

Aneuploidy often results in detrimental phenotypes because:

Accepted Answer

It leads to an imbalance in the amount of gene products, disrupting normal cellular function.

Question 7

Which of the following human aneuploid conditions is most compatible with survival, and why?

Accepted Answer

Trisomy 21, because chromosome 21 is small and carries fewer genes, reducing gene dosage imbalance.

Question 8

A woman aged 45 has a significantly higher risk of having a child with Down syndrome compared to a woman aged 25. What is the biological explanation for this increased risk?

Accepted Answer

Primary oocytes in older women have been arrested in prophase I for a longer time, increasing the likelihood of meiotic nondisjunction.

Question 9

Which of the following best explains why triploid plants, such as seedless watermelons, are sterile?

Accepted Answer

Triploid plants produce highly aneuploid gametes due to unequal separation of homologous chromosomes during meiosis.

Question 10

A plant breeder wants to produce a tetraploid plant from a diploid seedling. Which treatment would most effectively induce polyploidy, and what is the mechanism?

Accepted Answer

Treat with colchicine, which binds to tubulin and prevents proper chromosome segregation, promoting nondisjunction.

Question 11

During meiosis I, nondisjunction occurs in a cell with three pairs of chromosomes. What is the expected outcome for the gametes produced?

Accepted Answer

All four gametes will be abnormal, with two having $$n+1$$ chromosomes and two having $$n-1$$ chromosomes.

Question 12

Which of the following equations represents the gene product percentage for a chromosome present in only one copy (monosomy) in a diploid organism?

Accepted Answer

$$50\%$$

Question 13

Which of the following is a consequence of mitotic nondisjunction occurring early in embryonic development?

Accepted Answer

A subset of cells will be genetically different, resulting in mosaicism.

Question 14

Which of the following best describes allopolyploidy?

Accepted Answer

Combining chromosome sets from different species, followed by an increase in the number of sets.

Question 15

A polytene chromosome in Drosophila salivary glands is formed by repeated rounds of chromosome replication without cell division. If a chromosome pair doubles nine times, how many copies are present?

Accepted Answer

$$2^9 = 512$ copies

Question 16

Which of the following is NOT a use of chromosome banding patterns?

Accepted Answer

Increasing the number of chromosomes in a cell.

Question 17

A diploid plant species (2n) undergoes complete nondisjunction, resulting in a cell with all chromosomes. If this cell fuses with a normal haploid gamete (n), what is the chromosome number of the resulting individual?

Accepted Answer

$$3n$$

Question 18

Which of the following best explains why sex chromosome aneuploidies generally have less severe effects than autosomal aneuploidies?

Accepted Answer

X-chromosome inactivation converts additional X chromosomes into Barr bodies, reducing gene dosage imbalance.

Question 19

Which of the following is an example of autopolyploidy?

Accepted Answer

A plant species that increases its chromosome sets from diploid (2n) to tetraploid (4n) within the same species.

Variation in Chromosome Structure and Number (Chapter 8, Part 1) – Genetics Study Notes

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