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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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 6
Describe the major difference between sex determination in Drosophila and in humans.
Verified step by step guidance1
Understand that sex determination is the biological system that determines the development of sexual characteristics in an organism.
Recognize that in humans, sex determination is primarily based on the presence or absence of the Y chromosome: individuals with XY chromosomes develop as males, and those with XX chromosomes develop as females.
Note that in Drosophila (fruit flies), sex determination depends on the ratio of X chromosomes to sets of autosomes (non-sex chromosomes), rather than the presence of a Y chromosome.
Specifically, in Drosophila, a ratio of X chromosomes to autosome sets of 1.0 (e.g., 2X:2 sets of autosomes) results in a female, while a ratio of 0.5 (e.g., 1X:2 sets of autosomes) results in a male.
Summarize that the major difference is that humans use a chromosomal system based on the presence of the Y chromosome for sex determination, whereas Drosophila use the X chromosome to autosome ratio to determine sex.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Sex Determination in Drosophila
In Drosophila, sex is determined by the ratio of X chromosomes to sets of autosomes (X:A ratio). A ratio of 1.0 (e.g., XX) results in a female, while a ratio of 0.5 (e.g., XY) results in a male, regardless of the presence of a Y chromosome.
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Sex Determination
Sex Determination in Humans
Human sex determination depends on the presence or absence of the Y chromosome. Individuals with an XY chromosome pair develop as males due to the SRY gene on the Y chromosome, while XX individuals develop as females.
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Role of Chromosomes vs. Chromosome Ratios
The key difference lies in the mechanism: Drosophila uses the X-to-autosome ratio to determine sex, making the Y chromosome non-essential for maleness, whereas humans rely on the presence of the Y chromosome and its genes to trigger male development.
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Related Practice
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.
Textbook Question
What specific observations (evidence) support the conclusions about sex determination in Drosophila and humans?
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Textbook Question
Distinguish between the concepts of sexual differentiation and sex determination.
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Textbook Question
Contrast the XX/XY and XX/X0 modes of sex determination.
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