Question 1

Which of the following best describes the difference between homologous chromosomes and sister chromatids?

Accepted Answer

Homologous chromosomes contain the same genes at the same loci but may have different alleles, while sister chromatids are identical copies formed during DNA replication.

Question 2

During which phase of meiosis does crossing over occur, and what is its significance?

Accepted Answer

Crossing over occurs during late prophase I and increases genetic variation by exchanging DNA between non-sister chromatids.

Question 3

If a diploid organism has a haploid number $$n = 4$$, how many possible combinations of chromosomes can be produced in its gametes due to independent assortment alone?

Accepted Answer

$$2^4 = 16$

Question 4

A human cell with 47 chromosomes is most likely the result of which meiotic error?

Accepted Answer

Nondisjunction

Question 5

Which of the following statements about meiosis and mitosis is correct?

Accepted Answer

Meiosis involves two rounds of cell division after one round of chromosome duplication, while mitosis involves only one division.

Question 6

What is the primary evolutionary advantage of sexual reproduction as promoted by meiosis?

Accepted Answer

It increases genetic diversity, allowing populations to adapt to changing environments.

Question 7

A cell at the end of meiosis I in a human has how many chromosomes and what ploidy?

Accepted Answer

23 chromosomes, haploid

Question 8

Which event during meiosis is responsible for the random assortment of maternal and paternal chromosomes into gametes?

Accepted Answer

Independent orientation of homologous pairs during metaphase I

Question 9

A woman over the age of 40 has a higher risk of having a child with Down syndrome. What is the biological explanation for this increased risk?

Accepted Answer

Older eggs are more likely to undergo nondisjunction during meiosis I, leading to trisomy 21.

Question 10

Which of the following best explains why gametes produced by meiosis are genetically unique?

Accepted Answer

Each gamete receives a random combination of chromosomes due to independent assortment and crossing over.

Question 11

If nondisjunction occurs during meiosis II, what is the expected outcome in the resulting gametes?

Accepted Answer

Half the gametes will be normal, and half will have either an extra or missing chromosome.

Question 12

Which of the following is NOT a source of genetic variation in sexually reproducing organisms?

Accepted Answer

Replication of DNA during interphase

Question 13

A karyotype of a human cell shows three copies of chromosome 21. What is the ploidy and condition of this cell?

Accepted Answer

Diploid, trisomy 21

Question 14

Which of the following equations correctly represents the restoration of diploid chromosome number during fertilization?

Accepted Answer

$$n + n \rightarrow 2n$$

Question 15

Which process ensures that the chromosome number does not double with each generation in sexually reproducing organisms?

Accepted Answer

Meiosis

Question 16

Which of the following best describes aneuploidy?

Accepted Answer

A condition where cells have an abnormal number of chromosomes due to nondisjunction.

Question 17

Which phase of meiosis is most directly responsible for reducing the chromosome number from diploid to haploid?

Accepted Answer

Anaphase I

Question 18

Which of the following scenarios would most likely result in a zygote with monosomy?

Accepted Answer

Fertilization of an $$n - 1$$ gamete with a normal $$n$$ gamete

Question 19

Which of the following is a direct result of crossing over during meiosis?

Accepted Answer

Formation of recombinant chromosomes with new combinations of alleles

Meiosis: Mechanisms, Genetic Variation, and Errors

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