How many Barr bodies are found in a normal human female nucleus? In a normal male nucleus?

Verified step by step guidance

1. Understand what a Barr body is: it is an inactivated X chromosome found in the nuclei of cells in females, serving as a mechanism for dosage compensation between males and females.
2. Recall that normal human females have two X chromosomes (XX), while normal males have one X and one Y chromosome (XY).
3. Apply the formula for the number of Barr bodies: Number of Barr bodies = (Number of X chromosomes) - 1.
4. For a normal female (XX), calculate the number of Barr bodies as $X=2$, so Barr bodies = $2-1=1$.
5. For a normal male (XY), calculate the number of Barr bodies as $X=1$, so Barr bodies = $1-1=0$.

Key Concepts

Barr Body

A Barr body is an inactivated X chromosome found in the nuclei of female cells. It appears as a dense, dark-staining spot and represents the mechanism of dosage compensation to balance gene expression between males and females.

X Chromosome Inactivation

X chromosome inactivation is the process by which one of the two X chromosomes in females is randomly silenced during early embryonic development. This ensures that females, like males, have one functional copy of the X chromosome in each cell.

Sex Chromosome Composition in Humans

Normal human females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). This difference determines the number of Barr bodies: females typically have one Barr body, and males have none.