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10. Meiosis and Genetic Diversity — Practice Questions 3
This chapter explores how meiosis ensures chromosome reduction, generates variation through crossing-over and independent assortment, and how errors like nondisjunction affect genetic outcomes.
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(Multiple Choice — Click to Reveal Answer)
1. What is the role of meiosis in maintaining species chromosome number?
(A) It doubles the number before fertilization
(B) It produces diploid zygotes directly
(C) It halves the chromosome number in gametes
(D) It increases mutation rate
Answer
(C) — Meiosis reduces the chromosome number so fertilization restores the diploid state.
2. When during meiosis do homologous chromosomes align in pairs at the center of the cell?
(A) Metaphase II
(B) Anaphase I
(C) Metaphase I
(D) Telophase II
Answer
(C) — Homologous pairs align during metaphase I.
3. Which phase of meiosis is most responsible for reducing chromosome number?
(A) Prophase II
(B) Anaphase I
(C) Telophase II
(D) Interphase
Answer
(B) — Anaphase I separates homologs, halving the chromosome number.
4. What does crossing-over directly result in?
(A) Formation of chromatids
(B) Genetically identical gametes
(C) Mixing of maternal and paternal genes
(D) Increase in chromosome number
Answer
(C) — Crossing-over exchanges DNA between homologs, increasing variation.
5. What is the chromosomal composition of gametes produced by meiosis in humans?
(A) 46 chromosomes
(B) 23 diploid chromosomes
(C) 23 haploid chromosomes
(D) 46 haploid chromosomes
Answer
(C) — Human gametes contain 23 single (haploid) chromosomes.
6. In which stage are sister chromatids pulled apart during meiosis?
(A) Anaphase I
(B) Telophase I
(C) Metaphase I
(D) Anaphase II
Answer
(D) — Sister chromatids are separated in anaphase II.
7. Which of the following happens only in meiosis, not mitosis?
(A) Cytokinesis
(B) Chromatin condensation
(C) Tetrad formation
(D) Nuclear envelope breakdown
Answer
(C) — Only meiosis involves the pairing of homologous chromosomes into tetrads.
8. What causes genetic recombination in meiosis?
(A) Spindle fiber contraction
(B) Crossing-over between homologous chromosomes
(C) DNA replication
(D) Cytokinesis I
Answer
(B) — Crossing-over during prophase I produces recombination.
9. What results from a nondisjunction event during meiosis I?
(A) Four genetically identical gametes
(B) Gametes with normal chromosome number
(C) Gametes with extra or missing chromosomes
(D) Synapsis failure
Answer
(C) — Nondisjunction leads to abnormal gametes with incorrect chromosome counts.
10. What does the term “haploid” refer to?
(A) Having two sets of chromosomes
(B) Having four chromatids per chromosome
(C) Having one set of chromosomes
(D) Having three chromosomes per pair
Answer
(C) — Haploid cells contain one complete set of chromosomes.
11. What forms as a result of synapsis during meiosis I?
(A) Sister chromatids
(B) Centrosomes
(C) Tetrads
(D) Kinetochores
Answer
(C) — Synapsis is the pairing of homologous chromosomes, forming tetrads during prophase I.
12. Which type of reproduction involves meiosis?
(A) Asexual reproduction
(B) Binary fission
(C) Sexual reproduction
(D) Budding
Answer
(C) — Meiosis is essential for forming gametes in sexual reproduction.
13. How many total chromosomes are present in a human zygote?
(A) 23
(B) 46
(C) 92
(D) 69
Answer
(B) — A human zygote contains 46 chromosomes: 23 from each parent.
14. Which event is unique to prophase I of meiosis?
(A) DNA replication
(B) Chromatid separation
(C) Homologous chromosome pairing
(D) Spindle fiber formation
Answer
(C) — Homologs pair during prophase I, a feature not found in mitosis.
15. What is a primary cause of variation between siblings (excluding identical twins)?
(A) Identical mitosis
(B) Cytokinesis failure
(C) Crossing-over and independent assortment
(D) Diploid zygote formation
Answer
(C) — These two meiotic processes create genetically unique gametes, leading to sibling variation.
16. Which description best fits metaphase II of meiosis?
(A) Tetrads align in the center
(B) Sister chromatids align at the equator in haploid cells
(C) Homologous chromosomes pair up
(D) Nucleus reforms
Answer
(B) — In metaphase II, chromosomes line up individually in haploid cells.
17. Which outcome is most directly caused by meiosis in animals?
(A) Zygote formation
(B) Diploid daughter cells
(C) Production of haploid sperm and egg cells
(D) Formation of somatic cells
Answer
(C) — Meiosis produces gametes that are haploid, necessary for fertilization.
18. What happens during anaphase I of meiosis?
(A) Sister chromatids split
(B) Chromosomes replicate
(C) Homologous chromosomes move to opposite poles
(D) Nuclear envelope reforms
Answer
(C) — In anaphase I, homologous chromosomes separate, unlike anaphase II where chromatids separate.
19. How many gametes are typically formed from one diploid human cell completing meiosis?
(A) 1
(B) 2
(C) 3
(D) 4
Answer
(D) — Meiosis results in four haploid cells from one diploid cell.
20. Which of the following ensures that each gamete is genetically unique?
(A) DNA repair enzymes
(B) Cytoplasmic streaming
(C) Crossing-over and random chromosome assortment
(D) Nuclear envelope breakdown
Answer
(C) — These two meiotic processes introduce genetic variation in gametes.
21. During which phase are homologous chromosomes held together at chiasmata?
(A) Prophase II
(B) Metaphase I
(C) Anaphase II
(D) Telophase I
Answer
(B) — During metaphase I, homologous chromosomes are still connected at chiasmata and aligned on the metaphase plate.
22. Which structure helps chromosomes move during meiosis?
(A) Ribosome
(B) Centriole
(C) Spindle fibers
(D) Nucleolus
Answer
(C) — Spindle fibers attach to kinetochores and move chromosomes during division.
23. Which best describes the genetic content of cells after meiosis II?
(A) Haploid and genetically identical
(B) Diploid and genetically identical
(C) Haploid and genetically different
(D) Diploid and genetically different
Answer
(C) — Each haploid cell is genetically distinct due to crossing-over and independent assortment.
24. What type of division follows telophase II in meiosis?
(A) Replication
(B) Cytokinesis
(C) Synapsis
(D) Fertilization
Answer
(B) — Cytokinesis divides the cytoplasm, resulting in four separate haploid cells.
25. What does it mean when chromosomes "assort independently" during meiosis?
(A) Homologous chromosomes align in sequence
(B) Each chromosome separates without influence from others
(C) Sister chromatids pair randomly
(D) Chromosomes assort during telophase
Answer
(B) — During metaphase I, each homologous pair aligns independently of others, contributing to diversity.
26. What would most likely happen if recombination between homologous chromosomes failed during meiosis?
(A) Chromosomes would not replicate
(B) Genetic diversity in gametes would decrease
(C) The cell would become polyploid
(D) Sister chromatids would not form
Answer
(B) — Without recombination, there would be less genetic mixing, reducing variation in offspring.
27. A student observes a cell undergoing meiosis and notes that chromosomes are still duplicated but there is only one copy of each homologous pair. What stage is this?
(A) Prophase I
(B) Telophase II
(C) Prophase II
(D) Metaphase I
Answer
(C) — After meiosis I, cells are haploid but still contain duplicated chromosomes. Prophase II begins this next phase.
28. In an individual with a nondisjunction error during meiosis II, what percentage of resulting gametes would be abnormal?
(A) 0%
(B) 25%
(C) 50%
(D) 100%
Answer
(C) — If nondisjunction occurs in one meiosis II division, 2 of the 4 gametes will be abnormal.
29. Why do linked genes sometimes appear to assort independently in genetic crosses?
(A) They are located on different chromosomes
(B) Recombination breaks the linkage
(C) Their alleles are dominant
(D) They duplicate before meiosis
Answer
(B) — Crossing-over can separate linked genes if they are far apart on the chromosome.
30. Which of the following is most responsible for explaining why gametes from the same individual are genetically unique?
(A) DNA replication fidelity
(B) Cell membrane division
(C) Crossing-over and random chromosome alignment
(D) Telophase nuclear formation
Answer
(C) — These two meiotic events ensure that each gamete receives a unique set of alleles.
31. During which meiotic phase are recombined chromatids first visible as distinct chromosomes?
(A) Prophase I
(B) Anaphase II
(C) Metaphase I
(D) Telophase I
Answer
(A) — In prophase I, recombined chromatids become visible as chromosomes condense and crossing-over occurs.
32. Which of the following most directly contributes to Mendel's law of segregation?
(A) Alignment of chromosomes in metaphase II
(B) Synapsis during prophase I
(C) Separation of homologous chromosomes in anaphase I
(D) Formation of tetrads in metaphase I
Answer
(C) — The law of segregation is represented by the separation of homologous pairs during anaphase I.
33. A gamete has two copies of chromosome 13. Which process most likely failed?
(A) Fertilization
(B) Crossing-over
(C) Chromosome condensation
(D) Chromosome disjunction
Answer
(D) — Failure of proper separation (nondisjunction) can result in extra chromosomes in a gamete.
34. Why is genetic variation essential to the process of evolution?
(A) It ensures all offspring are identical
(B) It increases reproductive rate
(C) It allows populations to adapt to environmental changes
(D) It accelerates mitosis
Answer
(C) — Genetic diversity is key to a population's ability to evolve and survive changing conditions.
35. A chromosome map shows two genes are 48 map units apart. What does this indicate about their inheritance?
(A) They are likely inherited together
(B) Crossing-over between them is rare
(C) They are on different chromosomes
(D) They may assort independently due to frequent recombination
Answer
(D) — A distance greater than 50 map units suggests independent assortment due to frequent crossing-over.
36. What is a key genetic consequence of crossing-over during meiosis?
Answer
Crossing-over creates new combinations of alleles on chromosomes, increasing genetic variation among gametes and offspring.
37. Why is it important that gametes are haploid rather than diploid?
Answer
Haploid gametes ensure that when two gametes fuse during fertilization, the resulting zygote has the correct diploid chromosome number.
38. How can nondisjunction during meiosis lead to genetic disorders?
Answer
Nondisjunction causes gametes to have extra or missing chromosomes, which can result in disorders like Down syndrome (trisomy 21) or Turner syndrome (monosomy X).
39. Explain how meiosis contributes to genetic variation beyond just crossing-over.
Answer
Independent assortment during metaphase I leads to random combinations of maternal and paternal chromosomes in gametes, increasing genetic diversity.
40. What does the presence of polar bodies during oogenesis indicate about the division process?
Answer
It shows that most cytoplasm is conserved for one functional egg, while polar bodies discard excess chromosomes with minimal cytoplasm.
41. During which meiotic phase do chromosomes move toward opposite poles for the first time, and what is separating?
Answer
In anaphase I, homologous chromosomes—not sister chromatids—separate and move to opposite poles.
42. What is the difference in function between mitosis and meiosis in multicellular organisms?
Answer
Mitosis produces identical somatic cells for growth and repair, while meiosis produces genetically unique gametes for reproduction.
43. What is one reason why errors in meiosis can be more severe than errors in mitosis?
Answer
Meiotic errors affect gametes, which can lead to zygotes with genetic abnormalities that affect the entire organism.
44. How is recombination frequency used to determine gene distance on a chromosome?
Answer
Genes that recombine more frequently are farther apart; by measuring recombination rates, geneticists can map gene locations.
45. Describe how a diploid parent cell prepares for meiosis.
Answer
The cell replicates its DNA during interphase, forming duplicated chromosomes with sister chromatids before entering meiosis I.
46. What does it mean when chromosomes “segregate” during meiosis?
Answer
It means homologous chromosomes are separated into different gametes, ensuring each gamete receives only one copy of each gene.
47. Why does meiosis require two cell divisions, unlike mitosis?
Answer
The first division (meiosis I) reduces chromosome number, and the second (meiosis II) separates sister chromatids to ensure haploid gametes are formed.
48. What cellular structures are responsible for moving chromosomes during meiosis?
Answer
Spindle fibers, composed of microtubules, attach to kinetochores and pull chromosomes toward opposite poles during division.
49. How can the failure of proper spindle attachment affect meiosis?
Answer
If chromosomes do not attach correctly to spindle fibers, they may not segregate properly, leading to nondisjunction and aneuploid gametes.
50. Summarize two major sources of genetic variation introduced by meiosis.
Answer
(1) Crossing-over between homologous chromosomes during prophase I; (2) Independent assortment of chromosomes during metaphase I.