Final answer:
Examples of heterochromatin in a mammalian chromosome include the Barr body, centromeric DNA, telomeric DNA, and repetitive DNA. However, nucleosomes are not heterochromatin, but rather structural units of chromatin, and the entire X or Y chromosomes are not solely heterochromatic.
Step-by-step explanation:
The student asked which of the following are examples of heterochromatin in a mammalian chromosome, with options including a nucleosome, Barr body, repetitive DNA, X chromosome, Y chromosome, centromeric DNA, and telomeric DNA.
Heterochromatin is a tightly packed form of DNA or condensed chromatin. It is found in regions of the chromosome where genes are not typically expressed. Based on this definition, the examples of heterochromatin in a mammalian chromosome would be:
- Barr body: This is the inactivated X chromosome in female mammals and is an example of facultative heterochromatin.
- Centromeric DNA and telomeric DNA: These are structural parts of the chromosome that are essential for its stability and are typically heterochromatic.
- Repetitive DNA: Often found in heterochromatic regions like centromeres and telomeres.
However, a nucleosome is not an example of heterochromatin itself; instead, it is a fundamental unit of chromatin structure. Similarly, the entire X or Y chromosomes are not exclusively heterochromatic, although they have regions that are heterochromatic.