Textbook Question
Describe how nondisjunction in human female gametes can give rise to Klinefelter and Turner syndrome offspring following fertilization by a normal male gamete.
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Ch. 5 - Sex Determination and Sex Chromosomes
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 5, Problem 11
Given your answers to Problem 10, is it possible to distinguish between the Protenor and Lygaeus mode of sex determination based on the outcome of these crosses?
Verified step by step guidance1
Review the definitions of the Protenor and Lygaeus modes of sex determination. In the Protenor system, sex is determined by the presence of one or two X chromosomes (XX for female, X0 for male), whereas in the Lygaeus system, sex is determined by the presence of XY (male) or XX (female) chromosomes.
Recall the expected genotypes and phenotypes of offspring from crosses involving males and females under each system. For example, in the Protenor system, males have only one X chromosome and no Y, while in the Lygaeus system, males have both X and Y chromosomes.
Analyze the outcomes of the crosses from Problem 10, focusing on the sex ratios and the presence or absence of Y chromosomes in the progeny. Determine if the progeny phenotypes or genotypes differ in a way that can be attributed to either system.
Consider whether the phenotypic ratios or genetic markers observed in the offspring can uniquely identify the mode of sex determination. If both systems produce similar offspring ratios or phenotypes, it may not be possible to distinguish between them based solely on these crosses.
Summarize your conclusion by comparing the theoretical expectations of each system with the observed data from the crosses, explaining whether the data supports distinguishing between Protenor and Lygaeus modes or not.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Modes of Sex Determination
Sex determination systems define how sex chromosomes determine an organism's sex. The Protenor mode (XX/XO) involves females with two X chromosomes and males with one X and no Y, while the Lygaeus mode (XX/XY) has females with XX and males with XY chromosomes. Understanding these differences is key to interpreting genetic crosses.
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Guided course
04:24
Sex Determination
Genetic Cross Outcomes and Sex Ratios
Analyzing offspring sex ratios and genotypes from crosses helps infer the underlying sex determination system. In Protenor, males produce two types of gametes (X or no sex chromosome), while in Lygaeus, males produce X or Y gametes. Differences in progeny ratios can indicate which system is present.
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10:35Human Sex Chromosomes
Chromosomal Behavior During Meiosis
The segregation of sex chromosomes during meiosis affects gamete composition. In Protenor, males have an unpaired X chromosome that segregates randomly, producing gametes with or without X. In Lygaeus, X and Y chromosomes segregate into different gametes. This behavior influences the genetic makeup of offspring.
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05:30Meiosis Overview
Related Practice
Textbook Question
An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. Contrast the F1 and F2 generations from a cross between a female with reduced wings and a male with normal-sized wings when the female is the heterogametic sex.
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Textbook Question
An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. Contrast the F1 and F2 generations from a cross between a female with reduced wings and a male with normal-sized wings when the male is the heterogametic sex.
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Textbook Question
When cows have twin calves of unlike sex (fraternal twins), the female twin is usually sterile and has masculinized reproductive organs. This calf is referred to as a freemartin. In cows, twins may share a common placenta and thus fetal circulation. Predict why a freemartin develops.
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Textbook Question
An attached-X female fly, XXY, expresses the recessive X-linked white-eye mutation. It is crossed to a male fly that expresses the X-linked recessive miniature-wing mutation. Determine the outcome of this cross in terms of sex, eye color, and wing size of the offspring.
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Textbook Question
Assume that on rare occasions the attached X chromosomes in female gametes become unattached. Based on the parental phenotypes in Problem 12, what outcomes in the F₁ generation would indicate that this has occurred during female meiosis?
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