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

1. Identify the genetic abnormality associated with cri-du-chat syndrome, which is a terminal deletion on chromosome 5.
2. Review the karyotype analysis results for both parents and the child, focusing on chromosomes 5 and 12.
3. Determine if either parent has a balanced translocation involving chromosome 5, which could lead to an unbalanced gamete.
4. Consider the possible segregation patterns during meiosis in a parent with a balanced translocation, such as alternate, adjacent-1, or adjacent-2 segregation.
5. Identify which segregation pattern would result in a gamete with a terminal deletion on chromosome 5, leading to cri-du-chat syndrome in the child.

Key Concepts

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 on 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 affect offspring.

Karyotype Analysis

Karyotype analysis is a laboratory technique that visualizes an individual's chromosomes to identify chromosomal abnormalities. It involves arranging chromosomes in pairs and examining their structure and number. This analysis is crucial in diagnosing genetic disorders, such as cri-du-chat syndrome, and understanding the genetic contributions from both parents.

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 vital for grasping the genetic mechanisms behind the disorder.