3.2 Chromosomes

IB Syllabus Statements

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.

Describe what the technique of autoradiography helped us to learn about DNA molecules in chromosomes.
Describe the prokaryotic chromosome’s shape.
What are plasmids and where can they be found?
Outline how eukaryotic chromosomes are different from prokaryotic chromosomes.
Outline the relationship between a gene and chromosome.
Define homologous chromosomes using the terms gene and allele.
Compare diploid and haploid nuclei using the term homologous chromosome.
Outline the relationship between the term species and chromosome.
Describe how a karyogram is organized and what one shows.
Distinguish between sex chromosomes and autosomes.
Describe how you would determine the sex of an individual by analyzing it’s karyogram.
Outline Cairn’s technique for measuring the length of DNA molecules by auto radiography.
Compare the genome sizes of the following: T2 phage, E. Coli, D. melanogaster, H. sapiens, and P. japonica
Compare the diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza saliva, Parascaris equorum
Describe how you would diagnose Down syndrome using a karyogram.
Explain how you could use a database to identify the locus of a human gene and its polypeptide product.
Distinguish between the terms karyotype and karyogram.