Solutions For An Introduction to Genetic Analysis Chapter 2 Problem 16P

In the broad bean, the haploid chromosome set contains 4 m of DNA approximately. The average length of each chromosome is 4/9 m.

During metaphase, the chromosomes move to the equatorial plane of the cell. At this time, the average length of each chromosome is 13 µm. That is 13 X 10^--6 m.

Packing ratio = length of chromosome/ length of DNA molecule.

So, the average packing ratio at this stage will be:

Thus, it is 1:34,000 approximately.

Moreover, the packing is achieved by the interaction of DNA with proteins. The DNA double strand helix is coiled around molecular spools called nucleosomes. Each nucleosome is composed of eight proteins called histones. Histones are positively charged proteins and DNA is negatively charged. So, histones bind with DNA very tightly.

Thus, DNA-nucleosome chain is further coiled and folded during mitosis and is coiled into a solenoid. As the coil winds into loop around a central core of non-histone protein, is called as scaffold.