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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Multiple Choice

In the ZZ/ZW sex determination system, the male is…?

Heterogametic

Homogametic

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Understand the ZZ/ZW sex determination system: In this system, males are ZZ and females are ZW. This is opposite to the XY system where males are XY and females are XX.

Define 'homogametic': In genetics, 'homogametic' refers to the sex that has two of the same kind of sex chromosome. For example, in the ZZ/ZW system, males are homogametic because they have two Z chromosomes.

Define 'heterogametic': In genetics, 'heterogametic' refers to the sex that has two different kinds of sex chromosomes. In the ZZ/ZW system, females are heterogametic because they have one Z and one W chromosome.

Compare with the XY system: In the XY system, males are heterogametic (XY) and females are homogametic (XX). This is the opposite of the ZZ/ZW system.

Conclude the sex determination for males in the ZZ/ZW system: Since males have two identical Z chromosomes, they are considered homogametic in the ZZ/ZW system.

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Related Practice

Open Question

A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.

Propose a genetic hypothesis to explain these data.

Open Question

A wild-type Drosophila male and female are crossed, producing 324 female progeny and 161 male progeny. All their progeny are wild type.

Design an experiment that will test your hypothesis, using the wild-type progeny identified above. Describe the results you expect if your hypothesis is true.

Open Question

In chickens, a key gene involved in sex determination has recently been identified. Called DMRT1, it is located on the Z chromosome and is absent on the W chromosome. Like SRY in humans, it is male determining. Unlike SRY in humans, however, female chickens (ZW) have a single copy while males (ZZ) have two copies of the gene. Nevertheless, it is transcribed only in the developing testis. Working in the laboratory of Andrew Sinclair (a co-discoverer of the human SRY gene), Craig Smith and colleagues were able to 'knock down' expression of DMRT1 in ZZ embryos using RNA interference techniques (see Chapter 18). In such cases, the developing gonads look more like ovaries than testes [Nature 461: 267 (2009)]. What conclusions can you draw about the role that the DMRT1 gene plays in chickens in contrast to the role the SRY gene plays in humans?

Multiple Choice

Which of the follow sex chromosomes can be describes as homogametic?

Multiple Choice

In humans, which region on the Y chromosome determines maleness?

Multiple Choice

During meiosis the XY sex chromosomes segregate independently. Which of the following represents the gametes chromosomes after meiosis?

Open 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?

Open Question

How do we know that Drosophila utilizes a different sex-determination mechanism than mammals, even though it has the same sex-chromosome compositions in males and females?