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
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

3. Extensions to Mendelian Inheritance

Sex Chromosome

Genetics

3. Extensions to Mendelian Inheritance

Sex Chromosome

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1:46 minutes

Problem 5

Textbook Question

Describe the major difference between sex determination in Drosophila and in humans.

Verified step by step guidance

Understand that sex determination refers to the biological mechanism by which an organism develops as male or female. In both Drosophila (fruit flies) and humans, this process is influenced by chromosomes, but the mechanisms differ significantly.

In humans, sex determination is based on the presence of sex chromosomes (X and Y). Males are typically XY, and females are XX. The presence of the Y chromosome, specifically the SRY gene, triggers male development.

In Drosophila, sex determination is not based on the presence of a Y chromosome but rather on the ratio of X chromosomes to sets of autosomes (non-sex chromosomes). A ratio of 1.0 (e.g., two X chromosomes and two sets of autosomes) results in a female, while a ratio of 0.5 (e.g., one X chromosome and two sets of autosomes) results in a male.

Note that in humans, the Y chromosome is essential for male development, while in Drosophila, the Y chromosome is not involved in determining sex but is required for male fertility.

Summarize the major difference: In humans, sex determination is based on the presence of the Y chromosome and the SRY gene, while in Drosophila, it is determined by the X-to-autosome ratio.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Sex Determination Mechanisms

Sex determination refers to the biological system that determines the development of sexual characteristics in an organism. In Drosophila (fruit flies), sex is determined by the ratio of X chromosomes to autosomes, while in humans, it is determined by the presence of specific sex chromosomes (XX for females and XY for males).

X:A Ratio in Drosophila

In Drosophila, the X:A ratio is crucial for sex determination. This ratio compares the number of X chromosomes to the number of sets of autosomes. A ratio of 1 (two X chromosomes to two sets of autosomes) results in a female, while a ratio of 0.5 (one X chromosome to two sets of autosomes) results in a male, showcasing a unique genetic mechanism distinct from that of humans.

Chromosomal Sex Determination in Humans

Humans utilize a chromosomal sex determination system where the presence of the Y chromosome typically determines male sex. The SRY gene located on the Y chromosome initiates male development, while the absence of a Y chromosome leads to female development. This binary system contrasts with the more ratio-based system seen in Drosophila.