Introduction to
Chromosomes
a.
b.
e.
Eukaryotic Chromosomes
a. Drosophila polytene chromosomes. An Introduction to
Genetic Analysis, Griffiths et al., Fig. 8-4. b. Mouse mitotic
chromosomes, Genetics, Hartwell et al., Chapter 12 front
piece. c. Amphibian lampbrush chromosomes. Molecular
Biology of the Cell, Alberts et al., Fig. 8-16. d. Human
mitotic chromosomes (prophase), P. Lichter et al., 1990,
Science 247:64. e. Human mitotic chromosomes (metaphase,
disrupted). Epstein, unpublished data.
c.
d.
Haploid Chromosome Number (n)
The number of different
chromosomes in most cells of the
organism. The haploid number is
constant within a species, but
varies greatly between species. In
humans, n = 23.
Genome
The total DNA content (quantity and quality) of the
entire haploid chromosome set of an organism.
Diploid (2n)
Most higher organisms have two versions of each of
their chromosomes in most of their cells. Humans are
diploid. That means we have 2n, or 2 x 23 = 46
chromosomes in each of our cells. (We got one haploid
set from our mother, and the other haploid set from
our father.)