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 1d

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?

Verified step by step guidance

Understand the concept of X-chromosome inactivation: In mammalian females, one of the two X chromosomes in each cell is randomly inactivated during early embryonic development to ensure dosage compensation. This process is known as Lyonization.

Recognize the experimental evidence: Scientists have studied X-chromosome inactivation by analyzing the expression of genes on the X chromosome in female cells. They observed that some cells express genes from the paternal X chromosome, while others express genes from the maternal X chromosome.

Learn about the use of genetic markers: Researchers use genetic markers, such as polymorphisms or mutations, to distinguish between the maternal and paternal X chromosomes. By analyzing these markers in different cells, they can determine which X chromosome is active in each cell.

Understand clonal analysis: During development, cells divide and form clones. If X-chromosome inactivation were not random, all cells in a clone would express the same X chromosome. However, studies show that cells within a clone can express either the maternal or paternal X chromosome, supporting the randomness of the process.

Review studies on mosaicism: Female mammals are genetic mosaics for X-linked traits due to random X-chromosome inactivation. For example, in calico cats, the random inactivation of X chromosomes carrying different coat color genes results in the characteristic patchy fur pattern, providing visual evidence of the randomness of this process.

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Key Concepts

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

X Chromosomal Inactivation

X chromosomal inactivation is a process in female mammals where one of the two X chromosomes is randomly silenced during early embryonic development. This ensures dosage compensation, balancing the gene expression between males (XY) and females (XX). The inactivated X chromosome forms a structure known as a Barr body, which is not expressed in the cell.

Random Selection

The random selection of which X chromosome to inactivate occurs early in development, meaning that in a female's cells, some will express genes from the paternal X chromosome while others will express genes from the maternal X chromosome. This randomness leads to a mosaic pattern of gene expression, which can be observed in traits such as coat color in calico cats, where patches of color correspond to the inactivation of different X chromosomes.

Evidence from Genetic Studies

Genetic studies, including those involving genetically modified mice and human cell lines, have provided evidence for the random nature of X inactivation. For instance, experiments that track the inheritance of traits linked to X chromosomes show that the inactivation pattern is not biased towards either parent, supporting the idea that the process is random and occurs independently in each cell during early development.

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Multiple Choice

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

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

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

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

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?

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Textbook Question

In the discussion, we have focused on sex differentiation, sex chromosomes, and genetic mechanisms involved in sex determination. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations, you should answer the following fundamental questions?

How do we know that in humans the X chromosomes play no role in human sex determination, while the Y chromosome causes maleness and its absence causes femaleness?

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Textbook Question

How do we know whether or not a heteromorphic chromosome such as the Y chromosome plays a crucial role in the determination of sex?

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Textbook Question

Write a short essay that discusses sex chromosomes as they contrast with autosomes.

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