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?

Verified step by step guidance

1. Step 1: Understand the concept of Barr bodies. Barr bodies are inactivated X chromosomes found in the nuclei of somatic cells. Normally, males (XY) have no Barr bodies, while females (XX) have one Barr body per cell. The number of Barr bodies is equal to the number of X chromosomes minus one.
2. Step 2: Analyze the data for males. Among 7500 newborn males, six have one Barr body. This suggests that these males have an extra X chromosome (XXY), which is indicative of Klinefelter syndrome.
3. Step 3: Analyze the data for females. Among 7500 newborn females, four have two Barr bodies, which suggests they have three X chromosomes (XXX). This condition is known as Triple X syndrome. Additionally, two females have no Barr bodies, which indicates they have only one X chromosome (XO), a condition known as Turner syndrome.
4. Step 4: Relate the findings to chromosomal abnormalities. The unusual number of Barr bodies in these infants is caused by variations in the number of sex chromosomes, which result from nondisjunction during meiosis. Nondisjunction is the failure of chromosomes to separate properly during gamete formation.
5. Step 5: Conclude that the presence of abnormal numbers of Barr bodies in these infants is a direct result of chromosomal aneuploidy, specifically conditions like Klinefelter syndrome (XXY), Triple X syndrome (XXX), and Turner syndrome (XO). These conditions arise due to errors in chromosome segregation during parental gamete formation.

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 a missing or incomplete X chromosome, typically resulting in a 45,X karyotype. In some cases, females with Turner syndrome may have no Barr bodies if they have only one X chromosome. However, variations can occur, leading to the presence of one or more Barr bodies in individuals with atypical chromosomal patterns, such as mosaicism.