Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

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Sanders 3rd Edition

Ch. 10 - Eukaryotic Chromosome Abnormalities and Molecular Organization

Problem 32a

Chapter 10, Problem 32a

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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Review the karyotype results for the child to identify any abnormalities in chromosome 5. Cri-du-chat syndrome is caused by a terminal deletion on the short arm of chromosome 5 (5p). Look for evidence of this deletion in the child's karyotype.

Compare the child's karyotype with the karyotypes of the parents. Determine if either parent carries a structural rearrangement, such as a balanced translocation, that could have contributed to the deletion in the child.

If a balanced translocation is present in one of the parents, analyze how this could lead to an unbalanced karyotype in the child. Specifically, consider how the segregation of chromosomes during meiosis could result in the loss of genetic material on chromosome 5.

Evaluate whether the observed deletion in the child's chromosome 5 matches the expected characteristics of cri-du-chat syndrome. This includes confirming that the deletion is terminal and affects the short arm (5p).

Conclude whether the child's karyotype is consistent with cri-du-chat syndrome based on the presence of the terminal deletion on chromosome 5 and the inheritance pattern observed in the family. Provide reasoning that ties the karyotype findings to the clinical diagnosis.

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Key Concepts

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

Cri-du-chat Syndrome

Cri-du-chat syndrome is a genetic disorder caused by a deletion of a portion of chromosome 5, specifically at the 5p15.2 locus. This condition is characterized by distinctive features such as a high-pitched cry resembling that of a cat, developmental delays, and various physical abnormalities. Understanding the genetic basis of this syndrome is crucial for analyzing the karyotype results and determining if the child's chromosomes align with the expected genetic profile.

Karyotype Analysis

Karyotype analysis is a laboratory technique used to visualize an individual's chromosomes, allowing for the assessment of chromosomal number and structure. This analysis can identify chromosomal abnormalities, such as deletions, duplications, or translocations, which are critical in diagnosing genetic disorders. In the context of cri-du-chat syndrome, examining the karyotype of the child will reveal whether the deletion on chromosome 5 is present, confirming the diagnosis.

Chromosomal Deletion

A chromosomal deletion refers to the loss of a segment of DNA from a chromosome, which can lead to the loss of genetic material and associated functions. In cri-du-chat syndrome, the deletion on chromosome 5 results in the absence of crucial genes that are necessary for normal development. Understanding the implications of such deletions is essential for interpreting karyotype results and assessing the genetic health of the child.

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Deletions

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Textbook Question

For the following crosses, determine as accurately as possible the genotypes of each parent, the parent in whom nondisjunction occurs, and whether nondisjunction takes place in the first or second meiotic division. Both color blindness and hemophilia, a blood-clotting disorder, are X-linked recessive traits. In each case, assume the parents have normal karyotypes.

A man who is color blind and a woman who is wild type have a son with Jacob syndrome (XYY) who has hemophilia.

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Textbook Question

A color-blind man and a woman who is wild type have a daughter with Turner syndrome (XO) who has normal color vision and blood clotting.

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Textbook Question

A man who is color blind and has hemophilia and a woman who is wild type have a daughter with triple X syndrome (XXX) who has hemophilia and normal color vision.

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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. Which parent has an abnormal karyotype? How can you tell? What is the nature of the abnormality?