A plant breeder would like to develop a seedless variety of cucumber from two existing lines. Line A is a tetraploid line, and line B is a diploid line. Describe the breeding strategy that will produce a seedless line, and support your strategy by describing the results of crosses.
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
6. Chromosomal Variation
Chromosomal Mutations: Aneuploidy
Problem 27b
Textbook Question
A boy with Klinefelter syndrome (47,XXY) is born to a mother who is phenotypically normal and a father who has the X-linked skin condition called anhidrotic ectodermal dysplasia. The mother's skin is completely normal with no signs of the skin abnormality. In contrast, her son has patches of normal skin and patches of abnormal skin. Using the appropriate genetic terminology, describe the meiotic mistake that occurred. Be sure to indicate in which division the mistake occurred.

1
Understand the genetic basis of Klinefelter syndrome (47,XXY): This condition arises when an individual has two X chromosomes and one Y chromosome. This indicates a nondisjunction event during meiosis, where chromosomes fail to separate properly.
Analyze the inheritance of the X-linked condition (anhidrotic ectodermal dysplasia): Since the father has the X-linked condition, he can only pass on his X chromosome with the mutation to his offspring. The mother, being phenotypically normal, contributes one of her X chromosomes.
Explain the son's phenotype: The son has patches of normal skin and patches of abnormal skin. This is due to X-inactivation (lyonization), where one X chromosome is randomly inactivated in each cell. This leads to a mosaic pattern of expression for the X-linked condition.
Determine the meiotic mistake: The presence of two X chromosomes in the son suggests that nondisjunction occurred in the mother during meiosis. Specifically, the mistake likely occurred during meiosis I, where homologous chromosomes (the two X chromosomes) failed to separate, resulting in an egg with two X chromosomes.
Summarize the genetic event: The son inherited one X chromosome from the father (carrying the mutation) and two X chromosomes from the mother (due to nondisjunction in meiosis I). This explains the 47,XXY karyotype and the mosaic skin phenotype due to X-inactivation.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Klinefelter Syndrome
Klinefelter syndrome is a genetic condition in males characterized by the presence of an extra X chromosome, resulting in a 47,XXY karyotype. This condition can lead to various physical and developmental features, including infertility, reduced testosterone levels, and sometimes learning difficulties. Understanding this syndrome is crucial for analyzing the genetic implications of the meiotic error that led to the boy's condition.
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Human Sex Chromosomes
Meiosis and Chromosomal Nondisjunction
Meiosis is the process of cell division that produces gametes (sperm and eggs) with half the number of chromosomes. Nondisjunction is a meiotic error where chromosomes fail to separate properly during anaphase, leading to gametes with an abnormal number of chromosomes. In the case of Klinefelter syndrome, nondisjunction during meiosis I or II can result in the formation of a sperm or egg with an extra X chromosome, which contributes to the 47,XXY karyotype.
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Meiosis Steps
X-Linked Inheritance
X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. Conditions like anhidrotic ectodermal dysplasia are passed down through the X chromosome, affecting males more severely due to their single X chromosome. In this scenario, the mother's normal phenotype indicates she is likely a carrier, which is important for understanding the inheritance patterns and the genetic background of the boy's skin condition.
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X-Inactivation
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