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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1:37 minutes

Problem 30

Textbook Question

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A^m and A^p). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.
Assume that each gamete resulting from Problem 29 fuses, in fertilization, with a normal haploid gamete. What combinations will result? What percentage of zygotes will be diploid, containing one paternal and one maternal member of each chromosome pair?

Verified step by step guidance

Step 1: Understand the problem. The question involves a diploid cell with three pairs of chromosomes (AA, BB, CC), each with a maternal (m) and paternal (p) member. The task is to analyze the chromatid combinations during mitosis and meiosis, and then determine the zygotic combinations after fertilization with a normal haploid gamete.

Step 2: Recall the process of meiosis. Meiosis involves two rounds of division: Meiosis I (reductional division) separates homologous chromosomes, and Meiosis II (equational division) separates sister chromatids. During Meiosis I, homologous chromosomes pair up (synapsis) and may exchange genetic material through crossing over. This results in gametes with one chromosome from each pair (haploid).

Step 3: Consider the gametes produced in Problem 29. Each gamete will contain one chromosome from each pair (e.g., A^m, B^p, C^m or A^p, B^m, C^p). These gametes are haploid and will fuse with a normal haploid gamete during fertilization. The normal haploid gamete will also contain one chromosome from each pair, but the source (maternal or paternal) will depend on the organism's genetic makeup.

Step 4: Analyze the combinations after fertilization. When a haploid gamete from Problem 29 fuses with a normal haploid gamete, the resulting zygote will be diploid. To determine the combinations, consider all possible pairings of chromosomes from the two gametes. For example, if the gamete from Problem 29 contains A^m, B^p, C^m, and the normal haploid gamete contains A^p, B^m, C^p, the resulting zygote will have one maternal and one paternal chromosome for each pair (A^mA^p, B^pB^m, C^mC^p).

Step 5: Calculate the percentage of zygotes with one maternal and one paternal chromosome for each pair. Since the gametes from Problem 29 and the normal haploid gamete are equally likely to contribute either a maternal or paternal chromosome for each pair, the probability of obtaining a zygote with one maternal and one paternal chromosome for all three pairs is determined by the independent assortment of chromosomes. Use the formula for independent assortment probabilities to calculate this percentage.

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Key Concepts

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

Mitosis

Mitosis is the process of cell division that results in two genetically identical daughter cells, each with the same number of chromosomes as the original cell. It involves several stages: prophase, metaphase, anaphase, and telophase, where chromosomes are replicated and then evenly distributed. Understanding mitosis is crucial for recognizing how diploid cells maintain their chromosome number during cell division.

Meiosis

Meiosis is a specialized form of cell division that reduces the chromosome number by half, resulting in four haploid gametes. It consists of two rounds of division: meiosis I, where homologous chromosomes are separated, and meiosis II, where sister chromatids are separated. This process is essential for sexual reproduction, as it ensures genetic diversity through recombination and independent assortment.

Chromatid Pairing and Fertilization

Chromatid pairing occurs during the S phase of the cell cycle when DNA is replicated, resulting in sister chromatids that are joined at the centromere. In the context of fertilization, when two haploid gametes fuse, they form a diploid zygote containing one maternal and one paternal chromosome from each pair. Understanding these concepts is vital for predicting the genetic combinations in the resulting zygotes after fertilization.

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Related Practice

Textbook Question

Considering Problem 15, predict the number of different haploid cells that could be produced by meiosis if a fourth chromosome pair (W1 and W2) were added.

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Textbook Question

A woman who sought genetic counseling is found to be heterozygous for a chromosomal rearrangement between the second and third chromosomes. Her chromosomes, compared to those in a normal karyotype, are diagrammed to the right.

Using a drawing, demonstrate how these chromosomes would pair during meiosis. Be sure to label the different segments of the chromosomes.

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Textbook Question

Consider a diploid cell that contains three pairs of chromosomes designated AA, BB, and CC. Each pair contains a maternal and a paternal member (e.g., A^m and A^p). Using these designations, demonstrate your understanding of mitosis and meiosis by drawing chromatid combinations as requested. Be sure to indicate when chromatids are paired as a result of replication and/or synapsis.

Draw all possible combinations of chromatids during the early phases of anaphase in meiosis II.

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Textbook Question

Assume that during meiosis I none of the C chromosomes disjoin at metaphase, but they separate into dyads (instead of monads) during meiosis II. How would this change the alignments that you constructed during the anaphase stages in meiosis I and II? Draw them.

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Textbook Question

A species of cereal rye (Secale cereale) has a chromosome number of 14, while a species of Canadian wild rye (Elymus canadensis) has a chromosome number of 28. Sterile hybrids can be produced by crossing Secale with Elymus.

Given that none of the chromosomes pair at meiosis I in the sterile hybrid (Hang and Franckowlak, 1984), speculate on the anaphase I separation patterns of these chromosomes.

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Textbook Question

A pair of homologous chromosomes in Drosophila has the following content (single letters represent genes):

Chromosome 1RNMDHBGKWU

Chromosome 2RNMDHBDHBGKWU

Diagram the pairing of these homologous chromosomes in prophase I.

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Multiple Choice

During which phase of meiosis could an error result in trisomy, and what is the mechanism by which this occurs?

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