Q25. During this stage the sister chromatids begin to separate.

Background

Topic: Cell Division – Meiosis and Mitosis

This question tests your understanding of the stages of cell division, specifically when sister chromatids are pulled apart.

Key Terms:

• Sister chromatids: Identical copies of a chromosome connected by a centromere.

• Separation: The process where chromatids are pulled to opposite poles of the cell.

Step-by-Step Guidance

1. Recall the stages of mitosis and meiosis, focusing on when chromatids separate.

2. In mitosis, this occurs during anaphase. In meiosis, consider both meiosis I and II.

3. Think about which phase in meiosis is most similar to anaphase of mitosis.

4. Identify the stage in meiosis where sister chromatids (not homologous chromosomes) are separated.

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Q26. Following this phase each individual cell is haploid.

Background

Topic: Meiosis – Chromosome Number Reduction

This question is about the point in meiosis when cells become haploid (having half the original chromosome number).

Key Terms:

• Haploid: A cell with one set of chromosomes (n).

• Diploid: A cell with two sets of chromosomes (2n).

• Meiosis I: The division that reduces chromosome number by half.

Step-by-Step Guidance

1. Recall the two main divisions in meiosis: meiosis I and meiosis II.

2. Consider which division separates homologous chromosomes, not sister chromatids.

3. After this division, each daughter cell has only one chromosome from each homologous pair.

4. Identify the phase after which cells are considered haploid.

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Q27. During this phase homologues separate.

Background

Topic: Meiosis – Homologous Chromosome Separation

This question focuses on the stage of meiosis when homologous chromosomes (not sister chromatids) are pulled apart.

Key Terms:

• Homologous chromosomes: Chromosome pairs, one from each parent, that are similar in shape and size.

• Separation: The process of moving to opposite poles of the cell.

Step-by-Step Guidance

1. Recall the difference between homologous chromosomes and sister chromatids.

2. Think about the stages of meiosis I and II, and which one involves homologous chromosomes.

3. Identify the phase in meiosis I where homologous chromosomes are separated to opposite poles.

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Q28. New genetic combinations upon which natural selection can act are present after this stage.

Background

Topic: Genetic Variation – Crossing Over and Independent Assortment

This question is about the stage in meiosis when genetic recombination occurs, creating new allele combinations.

Key Terms:

• Genetic recombination: The production of offspring with combinations of traits differing from those found in either parent.

• Crossing over: The exchange of genetic material between homologous chromosomes during meiosis.

• Independent assortment: The random distribution of homologous chromosomes during meiosis I.

Step-by-Step Guidance

1. Recall when crossing over occurs during meiosis.

2. Think about the stage after which chromosomes have exchanged genetic material.

3. Consider when independent assortment is established.

4. Identify the stage after which new genetic combinations are present in the resulting cells.

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Q29. Haploid chromosomes line up individually during this stage.

Background

Topic: Meiosis II – Chromosome Alignment

This question is about the stage in meiosis II when chromosomes (now haploid) align at the cell's equator.

Key Terms:

• Haploid: Having one set of chromosomes.

• Metaphase II: The stage in meiosis II when chromosomes line up at the metaphase plate.

Step-by-Step Guidance

1. Recall the stages of meiosis II.

2. Think about when chromosomes align at the center of the cell.

3. Consider the ploidy of the cells at this point in meiosis.

4. Identify the specific stage where haploid chromosomes line up individually.

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Q30a. How many units of DNA would you expect to be present in a gamete formed in this animal as a result of meiosis?

Background

Topic: DNA Content During Meiosis

This question tests your understanding of how DNA content changes during meiosis, specifically from a somatic (body) cell to a gamete (sex cell).

Key Terms and Concepts:

• Somatic cell: Any cell of the body except sperm and egg cells; typically diploid.

• Gamete: A reproductive cell (sperm or egg); haploid.

• Meiosis: The process that reduces the chromosome number by half, producing haploid gametes from diploid cells.

Step-by-Step Guidance

1. Start by identifying the DNA content of the somatic cell (given as 8.4 units).

2. Recall that somatic cells are diploid (2n), while gametes are haploid (n).

3. Determine how the DNA content changes from diploid to haploid during meiosis.

4. Set up the calculation to find the DNA content in a gamete, knowing it should be half that of a somatic cell.

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Q30b. Briefly explain why the number in (a) is significant – using your understanding of genetic variation.

Background

Topic: Genetic Variation and Meiosis

This question asks you to connect the reduction in DNA content to the importance of genetic diversity in sexually reproducing organisms.

Key Terms and Concepts:

• Genetic variation: Differences in DNA sequences among individuals.

• Fertilization: The fusion of two gametes to form a zygote.

• Significance of haploid gametes: Ensures that offspring have the correct chromosome number and allows for new genetic combinations.

Step-by-Step Guidance

1. Consider why it is important for gametes to have half the DNA content of somatic cells.

2. Think about what happens during fertilization and how chromosome number is restored.

3. Reflect on how meiosis introduces genetic variation (crossing over, independent assortment).

4. Prepare to explain how this variation is important for evolution and adaptation.

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