Understandings:

• Prokaryotes have one chromosome consisting of a circular DNA molecule
• Some prokaryotes also have plasmids but eukaryotes do not
• Eukaryote chromosomes are linear DNA molecules associated with histone proteins
• In a eukaryote species there are different chromosomes that carry different genes
• Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
• Diploid nuclei have pairs of homologous chromosomes
• Haploid nuclei have one chromosome of each pair
• The number of chromosomes is a characteristic feature of members of a species
• A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
• Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex

Applications:

• Cairns' technique for measuring the length of DNA molecules by autoradiography
• Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica
• Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa and Parascaris equorum
• Use of karyograms to deduce sex and diagnose Down syndrome in humans