In a recent cytogenetic study on 1021 cases of Down syndrome, 46 were the result of translocations, the most frequent of which was symbolized as t(14;21). What does this symbol represent, and how many chromosomes would you expect to be present in t(14;21) Down syndrome individuals?

Key Concepts

Translocation

Translocation is a genetic phenomenon where a segment of one chromosome breaks off and attaches to another chromosome. In the context of Down syndrome, a specific type of translocation can lead to the presence of an extra copy of chromosome 21, which is responsible for the condition. The notation t(14;21) indicates that a piece of chromosome 21 has been translocated to chromosome 14.

Chromosome Count in Down Syndrome

Individuals with Down syndrome typically have 47 chromosomes instead of the usual 46 due to the presence of an extra copy of chromosome 21. In cases of translocation Down syndrome, such as t(14;21), the total chromosome count remains 47, as the translocated segment does not create an additional full chromosome but rather alters the structure of existing ones.

Cytogenetics

Cytogenetics is the branch of genetics that studies the structure and function of chromosomes. It involves analyzing chromosomal abnormalities, such as those seen in Down syndrome, to understand their implications for health and development. Cytogenetic studies often utilize techniques like karyotyping to visualize and identify chromosomal changes, including translocations.