Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

9. Mitosis and Meiosis

Meiosis

Genetics

9. Mitosis and Meiosis

Meiosis

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2:04 minutes

Problem 5a

Textbook Question

The diploid number of the hypothetical animal Geneticus introductus is 2n = 36. Each diploid nucleus contains 3 ng of DNA in G₁.
What amount of DNA is contained in each nucleus at the end of the S phase?

Verified step by step guidance

Understand the problem: The diploid number (2n) of the organism is 36, and the DNA content in G₁ phase is 3 ng. The question asks for the DNA content at the end of the S phase, where DNA replication occurs.

Recall that during the S phase of the cell cycle, DNA replication takes place, doubling the amount of DNA in the nucleus. However, the chromosome number (2n = 36) remains the same because no cell division occurs during this phase.

Since the DNA content in G₁ is 3 ng, and the S phase doubles the DNA content, the DNA content at the end of the S phase will be twice the amount present in G₁.

Set up the calculation: Multiply the DNA content in G₁ (3 ng) by 2 to determine the DNA content at the end of the S phase. Use the formula:

DNA = 2 \times 3 ng

Conclude that the DNA content at the end of the S phase is double the G₁ content, which reflects the completion of DNA replication.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Diploid Number

The diploid number (2n) refers to the total number of chromosomes in a somatic cell, which in this case is 36 for the animal Geneticus introductus. This means that there are 18 pairs of homologous chromosomes, with one set inherited from each parent. Understanding the diploid number is crucial for determining the genetic content of the organism.

DNA Replication

DNA replication is the process by which a cell duplicates its DNA before cell division. During the S phase of the cell cycle, each chromosome is replicated, resulting in two sister chromatids for each chromosome. This means that the total amount of DNA in the nucleus doubles, which is essential for ensuring that each daughter cell receives an identical set of chromosomes.

S Phase

The S phase, or synthesis phase, is a part of the cell cycle where DNA replication occurs. It follows the G₁ phase and precedes the G₂ phase. During this phase, the amount of DNA in the nucleus increases as each chromosome is copied, leading to a temporary state where the amount of DNA is twice that of the G₁ phase, which is critical for proper cell division.

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Related Practice

Textbook Question

Our closest primate relative, the chimpanzee, has a diploid number of 2n = 48. For each of the following stages of M phase, identify the number of chromosomes present in each cell.

End of meiotic anaphase II

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Textbook Question

Our closest primate relative, the chimpanzee, has a diploid number of 2n = 48. For each of the following stages of M phase, identify the number of chromosomes present in each cell.

Meiotic metaphase I

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Textbook Question

Cohesion between sister chromatids, as well as tension created by the pull of kinetochore microtubules, is essential to ensure efficient separation of chromatids at mitotic anaphase or in meiotic anaphase II. Explain why sister chromatid cohesion is important, and discuss the role of the proteins cohesin and separase in sister chromatid separation.

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Textbook Question

The diploid number of the hypothetical animal Geneticus introductus is 2n = 36. Each diploid nucleus contains 3 ng of DNA in G₁.

Explain why a somatic cell of Geneticus introductus has the same number of chromosomes and the same amount of DNA at the beginning of mitotic prophase as one of these cells does at the beginning of prophase I of meiosis.

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Textbook Question

Explain how the behavior of homologous chromosomes in meiosis parallels Mendel's law of segregation for autosomal alleles D and d. During which stage of M phase do these two alleles segregate from one another?

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Textbook Question

Suppose crossover occurs between the homologous chromosomes in the previous problem. At what stage of M phase do alleles D and d segregate?

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Textbook Question

Define and discuss these terms:

(a) synapsis

(b) bivalents

(d) crossing over

(e) chromomeres