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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1:09 minutes

Problem 10

Textbook Question

Define and discuss these terms:
(a) synapsis
(b) bivalents
(c) chiasmata
(d) crossing over
(e) chromomeres
(f) sister chromatids
(g) tetrads
(h) dyad
(i) monads

Verified step by step guidance

Step 1: Define synapsis. Synapsis is the pairing of homologous chromosomes during prophase I of meiosis. This process allows homologous chromosomes to align closely along their lengths, facilitating genetic recombination.

Step 2: Define bivalents. Bivalents refer to the paired homologous chromosomes that are physically connected during synapsis in meiosis. Each bivalent consists of two chromosomes (one from each parent) and four chromatids.

Step 3: Define chiasmata. Chiasmata are the physical points of contact between homologous chromosomes where crossing over occurs. These are visible as X-shaped structures under a microscope and are crucial for genetic recombination.

Step 4: Define crossing over. Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis. This process increases genetic diversity by creating new combinations of alleles.

Step 5: Define sister chromatids, tetrads, dyads, monads, and chromomeres. Sister chromatids are identical copies of a chromosome connected by a centromere. Tetrads refer to the four chromatids present in a bivalent during meiosis. Dyads are pairs of sister chromatids formed after the separation of homologous chromosomes. Monads are single chromatids resulting from the division of dyads. Chromomeres are bead-like structures along the chromosome, representing regions of tightly coiled DNA.

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Key Concepts

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

Synapsis

Synapsis is the process during meiosis where homologous chromosomes pair up closely along their lengths. This pairing is crucial for the exchange of genetic material and occurs during prophase I of meiosis, facilitating genetic diversity in gametes.

Chiasmata

Chiasmata are the physical points where homologous chromosomes exchange genetic material during crossing over. They appear as X-shaped structures and are essential for genetic recombination, contributing to genetic variation in offspring.

Crossing Over

Crossing over is the process where segments of DNA are exchanged between homologous chromosomes during meiosis. This genetic exchange occurs at chiasmata and results in new combinations of alleles, enhancing genetic diversity in the resulting gametes.

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Related Practice

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

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?

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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

Contrast the genetic content and the origin of sister versus nonsister chromatids during their earliest appearance in prophase I of meiosis. How might the genetic content of these change by the time tetrads have aligned at the equatorial plate during metaphase I?

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Textbook Question

Given the end results of the two types of division, why is it necessary for homologs to pair during meiosis and not desirable for them to pair during mitosis?