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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1:51 minutes

Problem 1d

Textbook Question

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?

Verified step by step guidance

Understand the Bar-eye phenotype in Drosophila: The Bar-eye phenotype is a mutation in fruit flies (Drosophila melanogaster) that results in a reduced eye size compared to the wild type. This mutation is associated with a chromosomal duplication rather than a single nucleotide change.

Review the concept of gene duplication: Gene duplication involves the presence of an extra copy of a gene or a gene region on a chromosome. This can lead to altered gene dosage, which affects the phenotype. In contrast, a nucleotide sequence change typically alters the function of a single gene without changing its copy number.

Examine experimental evidence: Cytological studies (microscopic examination of chromosomes) in Drosophila have shown that the Bar-eye phenotype is associated with a visible duplication of a specific region on the X chromosome. This duplication can be observed as an extra band or segment on the chromosome.

Analyze genetic dosage effects: The severity of the Bar-eye phenotype correlates with the number of duplicated regions. For example, flies with one duplication (heterozygous) have a less severe phenotype than those with two duplications (homozygous). This dosage effect supports the idea that the phenotype is due to gene duplication rather than a single nucleotide change.

Consider molecular evidence: Modern molecular techniques, such as DNA sequencing, have confirmed that the Bar-eye phenotype is not caused by a point mutation or small nucleotide change in the gene sequence. Instead, it is due to the presence of an extra copy of the gene region, which alters the expression levels of the genes involved.

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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 or more copies of that gene within the genome. This can lead to phenotypic changes, such as the Bar-eye phenotype in Drosophila, as the extra gene copies can alter gene expression and function. Understanding this mechanism is crucial for distinguishing between mutations caused by duplication versus those caused by changes in nucleotide sequences.

Phenotypic Expression

Phenotypic expression refers to the observable traits or characteristics of an organism, which result from the interaction of its genotype with the environment. In the case of the Bar-eye phenotype, the specific eye shape and color are direct manifestations of underlying genetic changes. Analyzing phenotypic expression helps researchers link genetic alterations to visible traits, providing insights into the nature of mutations.

Molecular Techniques in Genetics

Molecular techniques, such as PCR, sequencing, and gene mapping, are essential tools in genetics for analyzing DNA and identifying mutations. These methods allow scientists to determine whether a phenotype is due to gene duplication or nucleotide changes by examining the structure and arrangement of genes. Utilizing these techniques provides a clearer understanding of the genetic basis of phenotypes, such as the Bar-eye trait in Drosophila.

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Related Practice

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. How many chromosomes will the hybrid have before chromosome doubling?

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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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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 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?

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

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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?