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. Diagram the pairing of the abnormal chromosomes.

Verified step by step guidance

1. Step 1: Understand the genetic basis of cri-du-chat syndrome. This disorder is caused by a terminal deletion on the short arm of chromosome 5 (5p). The deletion results in the loss of genetic material, leading to the characteristic symptoms of the syndrome.
2. Step 2: Review the karyotype analysis results for the parents and the child. Focus on identifying any structural abnormalities in chromosomes 5 and 12, such as deletions, translocations, or other rearrangements.
3. Step 3: Diagram the pairing of the abnormal chromosomes during meiosis. To do this, illustrate how the deleted chromosome 5 from the child aligns with the normal chromosome 5 from the parent. Use a visual representation to show the missing segment on chromosome 5p.
4. Step 4: Consider the possibility of a balanced translocation in one of the parents. If one parent has a balanced translocation involving chromosomes 5 and 12, this could explain the inheritance pattern and the occurrence of cri-du-chat syndrome in the child. Diagram how the translocated chromosome pairs with its homologous chromosome during meiosis.
5. Step 5: Label the diagram clearly to indicate the normal and abnormal chromosomes, the deleted region on chromosome 5, and any translocations involving chromosome 12. This will help visualize the genetic mechanism leading to the disorder.

Key Concepts

Karyotype Analysis

Karyotype analysis is a laboratory technique that involves the examination of an individual's chromosomes to identify genetic abnormalities. It provides a visual representation of the number and structure of chromosomes, allowing for the detection of deletions, duplications, or other chromosomal rearrangements. In this case, it is crucial for understanding the chromosomal basis of cri-du-chat syndrome and assessing the genetic status of the parents.

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 region. This condition is characterized by distinctive features such as a high-pitched cry resembling that of a cat, developmental delays, and various physical anomalies. Understanding this syndrome is essential for interpreting the karyotype results and the implications for the family.

Chromosomal Deletion

A chromosomal deletion occurs when a segment of a chromosome is missing or deleted, which can lead to genetic disorders due to the loss of essential genes. In cri-du-chat syndrome, the deletion affects critical genes on chromosome 5, resulting in the symptoms associated with the disorder. Recognizing the nature of chromosomal deletions is vital for understanding the genetic risks and potential outcomes for the couple's future pregnancies.