Chromosomes

GENERAL OVERVIEW + SKILLS:

• Prokaryotes have one single circular DNA molecules as a chromosome.

• Some prokaryotes also have plasmids but eukaryotes don't.

• Eukaryote chromosomes are linear DNA molecules associated with histone proteins.

• In a eukaryote species there are a characteristic number of different chromosomes each carrying different genes.

• Pairs of chromosomes with the same sequence of genes (not necessarily the same alleles) are "Homologous chromosomes"

• Diploid nuclei have pairs of homologous chromosomes.

• Haploid nuclei have one chromosome of each pair.

• Sister chromatids are the two DNA molecules formed by DNA replication before cell division

• two separate chromosomes are formed at the splitting of the centromere at the start of anaphase.

• A karyogram (a chart) shows the chromosomes of an organism in homologous pairs of decreasing length. (Karyotype is the number and type of chromosomes present in the nucleus)

• Sex chromosomes determine the gender of an individual and autosomes are chromosomes that do not determine sex.

SKILLS NEEDED:

• Understand Cairns’ technique for measuring the length of DNA molecules by autoradiography.

• Compare genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica. (selected for points of interest.Genome size comparative activity

• Use karyograms to compare diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum.

• Use karyograms to deduce sex and diagnose Down syndrome in humans.

• Use of databases to identify the locus of a human gene and its polypeptide product