1. Introduction to Chromosomes

2. 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 Epstein, unpublished data. a. b. e. c. d.

3. 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.)