Question

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance.

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.
a) Variation in DNA sequence along the chromosome.
b) Differences in chromosome size.
c) Chromatid length differences.
d) Nucleolus distribution on the chromosome.

Answer 1

The striped appearance of chromosomes stained by dyes like Giemsa is due to variations in the DNA sequence and consequently the degree of coiling of the chromosomal regions, with more tightly coiled areas binding more stain.

Step-by-step explanation:

The striped appearance of chromosomes, resulting from differential binding of stains like Giemsa stain, can be largely attributed to the variation in DNA sequence along the chromosome. This variation affects the degree of coiling, with regions of tightly coiled DNA and condensed proteins binding more stain and appearing as dark bands, while less coiled areas bind less stain and appear lighter.

This pattern of coiling relates to gene activity, as active regions are generally less tightly packed, making the correct answer to the student's question (a) Variation in DNA sequence along the chromosome, as these variations dictate the compactness of the chromosomal regions and subsequently the binding affinity for stains.