Biomedical Engineering Reference
In-Depth Information
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
X
Y
7. 6
A normal G banded male karyotype. (Photograph courtesy of Lisa
Osborne of the Institute of Genomic Medicine, UMDNJ-New Jersey
Medical School.)
7.4.1 Eukaryotic chromosome structure
To understand how changes to the number or structure of chromosomes
can affect the phenotype, it is important to fi rst understand how the DNA
is packaged into the chromosome and the behavior of chromosomes dur-
ing mitosis in somatic cells and meiosis in germ cells. These processes are
marked by the degree of coiling that the DNA molecule undergoes as the
cell progresses from interphase, when the DNA is in a relatively relaxed
state, to division, when the DNA undergoes a tremendous degree of coiling
to form chromosomes.
These changes are shown in Fig. 7.7. Briefl y, the DNA molecule is coupled
with protein molecules to form chromatin. This is done by winding the DNA
around histone molecules to produce the nucleosomes which then further
coil into looped domains. This coiling continues to build up thicker coiled
loops. There is thus an underlying coiled architecture to the forming chro-
mosome that provides a basis for the different staining techniques, which
produce alternating light and dark staining areas along the chromosome's
length. These bands refl ect the various degrees of folding of the looped
domains. The chromosome bands also defi ne regions of the genome that
