Textbook Question
How do we know that X chromosomal inactivation of either the paternal or maternal homolog is a random event during early development in mammalian females?
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Ch. 7 - Sex Determination and Sex Chromosomes
Klug12th EditionConcepts of Genetics ISBN: 9780135564776
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Table of contents
- Ch. 1 - Introduction to Genetics17
- Ch. 2 - Mitosis and Meiosis36
- Ch. 3 - Mendelian Genetics51
- Ch. 4 - Extensions of Mendelian Genetics74
- Ch. 5 - Chromosome Mapping in Eukaryotes51
- Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages46
- Ch. 7 - Sex Determination and Sex Chromosomes33
- Ch. 8 - Chromosome Mutations: Variation in Number and Arrangement40
- Ch. 9 - Extranuclear Inheritance31
- Ch. 10 - DNA Structure and Analysis43
- Ch. 11 - DNA Replication and Recombination44
- Ch. 12 - DNA Organization in Chromosomes30
- Ch. 13 - The Genetic Code and Transcription54
- Ch. 14 - Translation and Proteins47
- Ch. 15 - Gene Mutation, DNA Repair, and Transposition41
- Ch. 16 - Regulation of Gene Expression in Bacteria29
- Ch. 17 - Transcriptional Regulation in Eukaryotes41
- Ch. 18 - Post-transcriptional Regulation in Eukaryotes33
- Ch. 19 - Epigenetics33
- Ch. 20 - Recombinant DNA Technology44
- Ch. 21 - Genomic Analysis36
- Ch. 22 - Applications of Genetic Engineering and Biotechnology36
- Ch. 23 - Developmental Genetics37
- Ch. 24 - Cancer Genetics34
- Ch. 25 - Quantitative Genetics and Multifactorial Traits54
- Ch. 26 - Population and Evolutionary Genetics45
Chapter 7, Problem 4
Contrast the XX/XY and XX/X0 modes of sex determination.
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Begin by defining the XX/XY sex determination system: in this system, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The presence of the Y chromosome typically determines maleness due to the SRY gene.
Next, define the XX/X0 sex determination system: here, females have two X chromosomes (XX), but males have only one X chromosome and no second sex chromosome (X0, where '0' indicates the absence of a chromosome).
Explain how sex is determined in each system: in XX/XY, the presence or absence of the Y chromosome determines sex, while in XX/X0, sex is determined by the number of X chromosomes, with males having a single X and females having two.
Discuss the genetic and phenotypic consequences of these systems, such as how dosage compensation mechanisms might differ due to the presence or absence of the Y chromosome and how this affects gene expression.
Summarize the evolutionary and biological significance of these systems, noting that XX/XY is common in mammals, while XX/X0 is found in some insects like grasshoppers, highlighting differences in chromosome structure and inheritance patterns.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
XX/XY Sex Determination System
In the XX/XY system, typically found in mammals, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The presence of the Y chromosome, specifically the SRY gene, triggers male development, making this system chromosomal and gene-driven.
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Sex Determination
XX/X0 Sex Determination System
The XX/X0 system, common in some insects like grasshoppers, involves females with two X chromosomes (XX) and males with only one X chromosome (X0), where '0' indicates the absence of a second sex chromosome. Sex is determined by the number of X chromosomes rather than the presence of a Y chromosome.
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Mechanisms of Sex Determination
Sex determination mechanisms vary by species and involve genetic or chromosomal cues that direct sexual development. Understanding how the presence or absence of specific chromosomes or genes influences gonadal differentiation is key to contrasting different systems like XX/XY and XX/X0.
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Related Practice
Textbook Question
Write a short essay that discusses sex chromosomes as they contrast with autosomes.
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Textbook Question
How do mammals, including humans, solve the 'dosage problem' caused by the presence of an X and Y chromosome in one sex and two X chromosomes in the other sex?
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Textbook Question
Describe the major difference between sex determination in Drosophila and in humans.
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Textbook Question
Distinguish between the concepts of sexual differentiation and sex determination.
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Textbook Question
The phenotype of an early-stage human embryo is considered sexually indifferent. Explain why this is so even though the embryo's genotypic sex is already fixed.
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