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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0:29 minutes

Problem 31g

Textbook Question

Mutations in the IL2RG gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases in humans. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The IL2RG gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the IL2RG gene product (assume its length to be 375 amino acids).
Large deletion covering Exons 2 and 3

Verified step by step guidance

Understand the structure of the IL2RG gene: The IL2RG gene consists of eight exons, which are coding regions that contribute to the final mRNA and protein product. Exons 2 and 3 are part of this coding sequence.

Analyze the impact of a large deletion: A deletion covering Exons 2 and 3 would remove these coding regions from the gene. This would result in the absence of the corresponding mRNA sequence during transcription.

Predict the effect on the mRNA: The deletion would lead to a shorter mRNA transcript, missing the sequences encoded by Exons 2 and 3. This could disrupt the reading frame (frameshift mutation) or lead to the loss of critical functional domains in the protein.

Consider the impact on the protein: If the deletion causes a frameshift, the downstream codons would be misread, potentially introducing premature stop codons. This would result in a truncated and likely nonfunctional protein. If the reading frame is preserved, the protein would still lack the amino acids encoded by Exons 2 and 3, which could impair its function.

Relate to the immune system: The IL2RG protein is a component of cytokine receptors essential for immune system development. A nonfunctional or incomplete protein would disrupt cytokine signaling, leading to severe combined immunodeficiency disorder (SCID).

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Key Concepts

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

IL2RG Gene Function

The IL2RG gene encodes a protein that is a critical component of the common gamma chain (γc) of cytokine receptors. This protein is essential for the signaling of several interleukins, which are vital for the development and function of immune cells. Mutations in this gene can disrupt the formation of functional cytokine receptors, leading to severe immunodeficiency.

Mutations and Their Effects

Mutations in genes can lead to changes in the protein products they encode, potentially altering their function. In the case of large deletions, such as those affecting exons, the resulting protein may be truncated or completely absent. This can severely impair the immune system's ability to respond to infections, as seen in SCID cases linked to IL2RG mutations.

Exons and Gene Structure

Exons are the coding regions of a gene that are transcribed into mRNA and translated into proteins. The IL2RG gene consists of eight exons, and their integrity is crucial for producing a functional protein. Deletions that remove one or more exons can lead to a loss of essential protein domains, resulting in nonfunctional or dysfunctional proteins that cannot support normal immune system development.

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Some pre-mRNA is not synthesized.

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Textbook Question

Shown here are the amino acid sequences of the wild-type and three mutant forms of a short protein.

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Wild-type: Met-Trp-Tyr-Arg-Gly-Ser-Pro-Thr

Mutant 1: Met-Trp

Mutant 2: Met-Trp-His-Arg-Gly-Ser-Pro-Thr

Mutant 3: Met-Cys-Ile-Val-Val-Val-Gln-His _

Use this information to answer the following questions:

Using the genetic coding dictionary, predict the type of mutation that led to each altered protein.

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Textbook Question

Shown below are two homologous lengths of the alpha and beta chains of human hemoglobin. Consult a genetic code dictionary, and determine how many amino acid substitutions may have occurred as a result of a single nucleotide substitution. For any that cannot occur as a result of a single change, determine the minimal mutational distance.

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Textbook Question

Mutations in the IL2RG gene cause approximately 30 percent of severe combined immunodeficiency disorder (SCID) cases in humans. These mutations result in alterations to a protein component of cytokine receptors that are essential for proper development of the immune system. The IL2RG gene is composed of eight exons and contains upstream and downstream sequences that are necessary for proper transcription and translation. Below are some of the mutations observed. For each, explain its likely influence on the IL2RG gene product (assume its length to be 375 amino acids).

Deletion in Exon 2, in frame

446

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Textbook Question

Deletion in Exon 2, causing frameshift

Missense mutation