Introduction to Genetic Analysis 88

Introduction to Genetic Analysis 88 - 44200_03_p73-114...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
87 3.2 The nature of chromosomes complete set of 23 human chromosomes, there are ap- proximately 850 G-dark bands visible during a stage of mitosis called metaphase , which is just before the chro- mosome pairs are pulled apart. These bands have pro- vided a useful way of subdividing the various regions of chromosomes, and each band has been assigned a spe- cific number. The difference between dark- and light-staining re- gions was formerly believed to be caused by differences in the relative proportions of bases: the G-light bands were thought to be relatively GC-rich, and the G-dark bands AT-rich. However, it is now thought that the dif- ferences are too small to account for banding patterns. The crucial factor again appears to be chromatin pack- ing density: the G-dark regions are packed more densely, with tighter coils. Thus there is a higher density of DNA to take up the stain. In addition, G bands have been correlated to vari- ous other properties. For example, nucleotide-labeling
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.

Ask a homework question - tutors are online