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
- 19. Cancer Genetics29m
- 20. Quantitative Genetics1h 26m
- 21. Population Genetics50m
- 22. Evolutionary Genetics29m
9. Mitosis and Meiosis
Development of Animal Gametes
1: minutes
Problem 34
Textbook Question
Textbook QuestionKuliev and Verlinsky (2004) state that there was a relatively high number of separation errors at meiosis I. In these cases the centromere underwent a premature division, occurring at meiosis I rather than meiosis II. Regarding chromosome 21, what would you expect to be the chromosome 21 complement in the secondary oocyte in which you saw a single chromatid (monad) for chromosome 21 in the first polar body? If this secondary oocyte was involved in fertilization, what would be the expected consequences?
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Meiosis and Chromosome Segregation
Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four haploid cells. During meiosis I, homologous chromosomes are separated, while meiosis II separates sister chromatids. Errors in this process, such as premature centromere division, can lead to aneuploidy, where gametes have an abnormal number of chromosomes.
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Chromosome 21 and Down Syndrome
Chromosome 21 is one of the smallest human chromosomes and is associated with Down syndrome when there is an extra copy (trisomy 21). If a secondary oocyte has a single chromatid for chromosome 21, it indicates that one homologous chromosome was not properly segregated. If this oocyte is fertilized, it could lead to an embryo with an abnormal number of chromosome 21, potentially resulting in Down syndrome.
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Polar Bodies and Oocyte Development
During oocyte development, polar bodies are small cells that are produced alongside the oocyte during meiosis but typically do not develop into ova. The first polar body contains the genetic material that was not included in the secondary oocyte. The presence of a single chromatid in the first polar body suggests that the secondary oocyte may have an abnormal chromosomal complement, which can affect fertilization outcomes.
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