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

6. Chromosomal Variation

Chromosomal Rearrangements: Duplications

Genetics

6. Chromosomal Variation

Chromosomal Rearrangements: Duplications

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2:33 minutes

Problem 29

Textbook Question

Describe at least two mechanisms by which duplicate genes arise. What are the possible fates of duplicate genes? Does the mode of duplication affect possible fates?

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Duplicate genes can arise through two primary mechanisms: (1) Unequal crossing over during meiosis, where homologous chromosomes misalign, leading to one chromosome gaining an extra copy of a gene and the other losing it, and (2) Whole genome duplication (polyploidy), where an organism inherits an entire extra set of chromosomes, resulting in duplication of all genes.

Once duplicate genes are formed, they can have several possible fates: (1) One copy may accumulate mutations and become a pseudogene (nonfunctional), (2) One copy may retain the original function while the other evolves a new function (neofunctionalization), or (3) Both copies may share the original function, with each specializing in a subset of the original function (subfunctionalization).

The mode of duplication can influence the possible fates of duplicate genes. For example, duplicates arising from unequal crossing over are often tandem duplicates (located next to each other), which may be more prone to gene conversion events, potentially limiting their divergence. In contrast, duplicates from whole genome duplication are dispersed across the genome, reducing the likelihood of gene conversion and allowing for greater functional divergence.

Consider the evolutionary pressures acting on the duplicate genes. If the original gene function is essential, one copy is likely to be preserved under purifying selection, while the other may be free to evolve new functions or become nonfunctional.

Analyze the genomic context of the duplicate genes to predict their evolutionary trajectory. For example, tandem duplicates may face different selective pressures compared to dispersed duplicates, influencing their likelihood of neofunctionalization or subfunctionalization.

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Key Concepts

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

Gene Duplication

Gene duplication is a process where a segment of DNA is copied, resulting in two identical or similar genes. This can occur through various mechanisms, such as unequal crossing over during meiosis or retrotransposition, where RNA is reverse-transcribed into DNA. The presence of duplicate genes can lead to genetic redundancy, providing raw material for evolution and functional diversification.

Fates of Duplicate Genes

Duplicate genes can follow several evolutionary paths after their formation. They may become nonfunctional (pseudogenes), retain the same function, or acquire new functions through mutations. This functional divergence can lead to the development of new traits or adaptations, contributing to the organism's evolutionary fitness and complexity.

Modes of Duplication

The mode of gene duplication can influence the subsequent fates of the duplicate genes. For instance, tandem duplications, where genes are duplicated in close proximity, may lead to functional redundancy, while segmental duplications can result in larger genomic changes. The context of duplication, such as the genomic environment and selective pressures, plays a crucial role in determining whether duplicate genes will be preserved, lost, or repurposed.

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Textbook Question

A pair of homologous chromosomes in Drosophila has the following content (single letters represent genes):

Chromosome 1RNMDHBGKWU

Chromosome 2RNMDHBDHBGKWU

What term best describes the unusual structure that forms during pairing of these chromosomes?

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Textbook Question

Discuss Ohno's hypothesis on the role of gene duplication in the process of evolution. What evidence supports this hypothesis?

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Textbook Question

Dr. Ara B. Dopsis has an idea he thinks will be a boon to agriculture. He wants to create the 'pomato,' a hybrid between a tomato (Lycopersicon esculentum) that has 12 chromosomes and a potato (Solanum tuberosum) that has 48 chromosomes. Dr. Dopsis is hoping his new pomato will have tuber growth like a potato and the fruit production of a tomato. He joins a haploid gamete from each species to form a hybrid and then induces doubling of chromosome number. Will this hybrid be infertile?

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after an insertional duplication?

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Multiple Choice

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after an tandem duplication?

How do we know that the mutant Bar-eye phenotype in Drosophila is due to a duplicated gene region rather than to a change in the nucleotide sequence of a gene?

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Textbook Question

From the following list, identify the types of chromosome changes you expect to show phenotypic consequences. duplication

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