3.2 Chromosomes

Nature of science:

Developments in research follow improvements in techniques—autoradiography was used to establish the length of DNA molecules in chromosomes. (1.8)

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 and skills:

Application: Cairns’ technique for measuring the length of DNA molecules by autoradiography.

Application: Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica.

Application: Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum.

Application: Use of karyograms to deduce sex and diagnose Down syndrome in humans.

Skill: Use of databases to identify the locus of a human gene and its polypeptide product.

DBQs

DBQ 153

DBQ156