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

17. Mutation, Repair, and Recombination

Types of Mutations

Genetics

17. Mutation, Repair, and Recombination

Types of Mutations

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1:51 minutes

Problem 3

Textbook Question

When working on barley plants, two researchers independently identify a short-plant mutation and develop homozygous recessive lines of short plants. Careful measurements of the height of mutant short plants versus normal tall plants indicate that the two mutant lines have the same height. How would you determine if these two mutant lines carry mutation of the same gene or of different genes?

Verified step by step guidance

Step 1: Understand the problem. The researchers have two homozygous recessive mutant lines of barley plants that are short in height. The goal is to determine if the mutations causing the short phenotype are in the same gene or in different genes. This can be done using a genetic complementation test.

Step 2: Perform a genetic complementation test. Cross the two mutant lines with each other to produce F1 offspring. This involves mating plants from one mutant line with plants from the other mutant line.

Step 3: Analyze the phenotype of the F1 offspring. If the F1 offspring are all tall (wild-type phenotype), it indicates that the mutations are in different genes, as each mutant line provides a functional copy of the gene that the other line lacks. This is called complementation.

Step 4: If the F1 offspring are all short (mutant phenotype), it indicates that the mutations are in the same gene. In this case, neither mutant line can provide a functional copy of the gene, so the short phenotype persists.

Step 5: Conclude based on the results of the complementation test. If complementation occurs (tall F1 plants), the mutations are in different genes. If no complementation occurs (short F1 plants), the mutations are in the same gene.

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Key Concepts

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

Homozygosity and Recessive Traits

Homozygosity refers to having two identical alleles for a particular gene, which can be either dominant or recessive. In the context of the short-plant mutation in barley, the homozygous recessive lines indicate that both alleles are for the short phenotype. Understanding this concept is crucial because it helps in determining how traits are inherited and expressed in offspring, particularly when analyzing genetic mutations.

Genetic Complementation Test

A genetic complementation test is a method used to determine whether two mutations that produce similar phenotypes are in the same gene or in different genes. By crossing the two mutant lines and observing the phenotype of the offspring, researchers can infer whether the mutations complement each other (indicating different genes) or fail to complement (indicating the same gene). This test is essential for understanding the genetic basis of traits.

Phenotypic Analysis

Phenotypic analysis involves studying the observable characteristics of an organism, which result from the interaction of its genotype with the environment. In this case, measuring the height of the barley plants provides data on the expression of the short-plant mutation. By comparing the phenotypes of the mutant lines and their progeny, researchers can gather evidence to support conclusions about the genetic relationships between the mutations.

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Textbook Question

Go online to the Online Mendelian Inheritance of Man (OMIM) website. Look up the following genetic conditions and answer the questions posed about them.

Look up cystic fibrosis (CF), OMIM 602421, and give the gene name and abbreviation and the chromosome location of the gene.

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Textbook Question

Go online to the Online Mendelian Inheritance of Man (OMIM) website. Look up the following genetic conditions and answer the questions posed about them.

Go to the 'Population Genetics' section discussing the TSD gene. In a few sentences, summarize the human population in which TSD is most frequently found and give the approximate frequency of heterozygous carriers for the TSD mutation in North American Jews.

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Textbook Question

Go online to the Online Mendelian Inheritance of Man (OMIM) website. Look up the following genetic conditions and answer the questions posed about them.

Look up Tay–Sachs disease (TSD), OMIM number 272800, and give the name and abbreviation of the affected gene and the chromosome location of the gene.

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Textbook Question

For the retinal cancer retinoblastoma, the inheritance of one mutated copy of RB1 from one of the parents is often referred to as a mutation that produces a 'dominant predisposition to cancer.' This means that the first mutation does not produce cancer but makes it very likely that cancer will develop.

Explain why cancer is almost certain to develop with the inheritance of one mutated copy of RB1.

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Textbook Question

What is the difference between a transition mutation and a transversion mutation?

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Textbook Question

Price et al. [(1999). J. Bacteriol. 181:2358–2362] conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within the 2294-nucleotide gene in 26 strains they identified five point mutations—two missense and three synonyms—among different isolates. Necropsy samples from an anthrax outbreak in 1979 revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different B. anthracis strains.

On what basis did the authors conclude that evidence of horizontal transfer is absent from their data?

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Textbook Question

Which types of nucleotide changes (missense or synonyms) cause amino acid changes?

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Textbook Question

Explain the following processes involving chromosome mutations and cancer development.

How the chromosome mutation producing Burkitt lymphoma generates the disease.

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