How can karyograms be used to determine sex and diagnose Down Syndrome in humans?

Sourav PanNovember 8, 2024

Answered

Karyograms are powerful tools in cytogenetics that can be used to determine an individual’s sex and diagnose genetic conditions such as Down syndrome. Here’s how karyotyping works for these purposes:

Determining Sex Using Karyograms

1. Chromosome Composition:
   • A karyotype displays the complete set of chromosomes in an individual, arranged in pairs based on size, shape, and banding patterns. In humans, there are 22 pairs of autosomes and 1 pair of sex chromosomes (XX or XY).
2. Identification of Sex Chromosomes:
   • The sex of an individual can be determined by examining the sex chromosomes:
     • Females typically have two X chromosomes (XX), which appear as a pair in the karyogram.
     • Males have one X and one Y chromosome (XY), which can be identified by the smaller size of the Y chromosome compared to the X chromosome.
   • This chromosomal analysis allows for clear identification of the biological sex based on the presence or absence of specific sex chromosomes.

Diagnosing Down Syndrome Using Karyograms

1. Karyotype Analysis:
   • Down syndrome, also known as trisomy 21, is characterized by the presence of an extra copy of chromosome 21. A karyotype test involves analyzing a sample of blood or other tissues to count and examine the chromosomes .
2. Identification of Chromosomal Abnormalities:
   • In a karyotype for an individual with Down syndrome, there will be three copies of chromosome 21 instead of the usual two. This is represented as 47, XX, +21 for females or 47, XY, +21 for males .
   • Karyotyping allows clinicians to visualize this abnormality directly by comparing the number and structure of chromosomes against a standard karyotype.
3. Prenatal and Postnatal Testing:
   • Karyotyping can be performed during pregnancy (via amniocentesis or chorionic villus sampling) to assess the risk or confirm a diagnosis of Down syndrome in a fetus . After birth, it can also be used to confirm a diagnosis if physical signs suggest Down syndrome