In a large metropolitan hospital, cells from newborn babies are collected and examined microscopically over a 5-year period. Among approximately 7500 newborn males, six have one Barr body in the nuclei of their somatic cells. All other newborn males have no Barr bodies. Among 7500 female infants, four have two Barr bodies in each nucleus, two have no Barr bodies, and the rest have one. What is the cause of the unusual number of Barr bodies in a small number of male and female infants?

Key Concepts

Barr Bodies

Barr bodies are inactivated X chromosomes found in the nuclei of female cells. In typical females, one X chromosome is active while the other is condensed into a Barr body. This process, known as X-inactivation, ensures dosage compensation between males (XY) and females (XX) in terms of X-linked gene expression.

Klinefelter Syndrome

Klinefelter syndrome is a genetic condition in males characterized by the presence of an extra X chromosome, resulting in a 47,XXY karyotype. Males with this condition typically have one Barr body due to the inactivation of one of the X chromosomes. This syndrome can lead to various physical and developmental traits, including infertility and reduced testosterone levels.

Turner Syndrome

Turner syndrome occurs in females who have only one X chromosome (45,X) or have a partially missing second X chromosome. In cases where females have two Barr bodies, it may indicate the presence of an additional X chromosome, as seen in conditions like Triple X syndrome (47,XXX). This can lead to a range of physical and developmental features, but many individuals may be asymptomatic.