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: Deletions

Genetics

6. Chromosomal Variation

Chromosomal Rearrangements: Deletions

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2:26 minutes

Problem 32e

Textbook Question

A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a disorder caused by a terminal deletion of chromosome 5. Their physician orders karyotype analysis of both parents and of the child. The karyotype results for chromosomes 5 and 12 are shown here. What segregation pattern occurred to produce the gamete involved in fertilization of the child with cri-du-chat syndrome?

Verified step by step guidance

Understand the genetic basis of cri-du-chat syndrome: This syndrome is caused by a terminal deletion on the short arm of chromosome 5 (5p). This deletion results in the loss of genetic material, leading to the characteristic symptoms of the disorder.

Analyze the karyotype results: Carefully examine the karyotype data provided for chromosomes 5 and 12 in the parents and the child. Look for any structural abnormalities, such as translocations, deletions, or duplications, in the parental chromosomes that could explain the origin of the deletion in the child.

Determine if a balanced translocation is present in one of the parents: A balanced translocation occurs when two chromosomes exchange segments without any loss or gain of genetic material. If one parent carries a balanced translocation involving chromosome 5, this could lead to an unbalanced gamete during meiosis, resulting in the deletion observed in the child.

Identify the segregation pattern during meiosis: If a parent has a balanced translocation, consider the possible segregation patterns during meiosis. Specifically, focus on adjacent-1 segregation, which can produce gametes with unbalanced chromosomal content. This could lead to the terminal deletion on chromosome 5 in the child.

Conclude the segregation pattern: Based on the karyotype analysis and the presence of a balanced translocation in one parent, the most likely segregation pattern is adjacent-1 segregation. This pattern would result in the gamete carrying the unbalanced chromosomal content (the terminal deletion on chromosome 5) that contributed to the child’s cri-du-chat syndrome.

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Key Concepts

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

Chromosomal Deletion

Chromosomal deletion refers to the loss of a segment of a chromosome, which can lead to genetic disorders. In the case of cri-du-chat syndrome, a terminal deletion of chromosome 5 results in the loss of critical genes, leading to the characteristic symptoms of the disorder. Understanding this concept is essential for analyzing how such deletions can occur and their implications for offspring.

Karyotype Analysis

Karyotype analysis is a laboratory technique used to visualize an individual's chromosomes, allowing for the identification of chromosomal abnormalities such as deletions, duplications, or aneuploidies. This analysis is crucial in diagnosing genetic disorders and understanding the genetic makeup of individuals, particularly in cases of suspected chromosomal syndromes like cri-du-chat.

Segregation Patterns

Segregation patterns refer to the distribution of alleles during gamete formation, as described by Mendel's laws of inheritance. In the context of this question, understanding how chromosomes segregate during meiosis can help explain how a gamete with a deletion on chromosome 5 could lead to the fertilization event resulting in cri-du-chat syndrome. This concept is fundamental for grasping the genetic mechanisms behind inherited disorders.

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

Terminal deletion

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The mutations called bobbed in Drosophila result from variable reductions (deletions) in the number of amplified genes coding for rRNA. Researchers trying to maintain bobbed stocks have often documented their tendency to revert to wild type in successive generations. Propose a mechanism based on meiotic recombination which could account for this reversion phenomenon. Why would wild-type flies become more prevalent in Drosophila cultures?

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Textbook Question

A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a disorder caused by a terminal deletion of chromosome 5. Their physician orders karyotype analysis of both parents and of the child. The karyotype results for chromosomes 5 and 12 are shown here. Do the karyotypes of the parents help explain the occurrence of the three previous spontaneous abortions? Explain.

325

views

Textbook Question

A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a disorder caused by a terminal deletion of chromosome 5. Their physician orders karyotype analysis of both parents and of the child. The karyotype results for chromosomes 5 and 12 are shown here. What is the approximate probability that the next child of this couple will have cri-du-chat syndrome?

A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a disorder caused by a terminal deletion of chromosome 5. Their physician orders karyotype analysis of both parents and of the child. The karyotype results for chromosomes 5 and 12 are shown here. Which parent has an abnormal karyotype? How can you tell? What is the nature of the abnormality?

332

views

Textbook Question

A healthy couple with a history of three previous spontaneous abortions has just had a child with cri-du-chat syndrome, a disorder caused by a terminal deletion of chromosome 5. Their physician orders karyotype analysis of both parents and of the child. The karyotype results for chromosomes 5 and 12 are shown here. Are the chromosomes in the child consistent with those expected in a case of cri-du-chat syndrome? Explain your reasoning.

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