Essential Idea:
Chromosomes carry genes in a linear sequence
that is shared by members of a species
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
Skills:
- Use of databases to identify the locus of a human gene and its polypeptide product