1. Prokaryotes have one chromosome consisting of a circular DNA molecule.

• Describe the arrangement of prokaryotic DNA (nucleoid and plasmid).

• Define the term “naked” in relation to prokaryotic DNA.

2. Some prokaryotes also have plasmids but eukaryotes do not.

• Describe the structure and function of plasmid DNA.

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

• Describe the structure of eukaryotic DNA and associated histone proteins during interphase (chromatin).

• Explain why chromatin DNA in interphase is said to look like “beads on a string.”

4. In a eukaryote species there are different chromosomes that carry different genes.

• List three ways in which the types of chromosomes within a single cell are different.

• State the number of nuclear chromosome types in a human cell.

5. Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.

• Define homologous chromosome.

• State a similarity and a difference found between pairs of homologous chromosomes.

6. Diploid nuclei have pairs of homologous chromosomes.

• Define diploid.

• State the human cell diploid number.

• Outline the formation of a diploid cell from two haploid gametes.

• State an advantage of being diploid.

7. Haploid nuclei have one chromosome of each pair.

• Define haploid.

• State the human cell haploid number.

• List example haploid cells.

8. The number of chromosomes is a characteristic feature of members of a species.

• State that chromosome number and type is a distinguishing characteristic of a species.

• List mechanisms by which a species chromosome number can change.

9. A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.

• Describe the process of creating a karyogram.

• List the characteristics by which chromosomes are arranged on the karyogram.

guidance: The terms karyotype and karyogram have different meanings. Karyotype is a property of a cell—the number and type of chromosomes present in the nucleus, not a photograph or diagram of them.

10. Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.

• Outline the structure and function of the two human sex chromosomes.

• Outline gender determination by sex chromosomes.

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

• Describe Cairn’s technique for producing images of DNA molecules from E. coli.

• Outline conclusions drawn from the images produced using Cairn’s autoradiography technique.

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

• Describe the two procedures for obtaining fetal cells for production of a karyotype.

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

• State the minimum chromosome number in eukaryotes.

• Explain why the typical number of chromosomes in a species is always an even number.

• Explain why the chromosome number of a species does not indicate the number of genes in the species.

• Explain the relationship between the number of human and chimpanzee chromosomes.

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

• Distinguish between a karyogram and a karyotype.

• Deduce the sex of an individual given a karyogram.

• Describe the use of a karyogram to diagnose Down syndrome.

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

• The terms karyotype and karyogram have different meanings. Karyotype is a property of a cell—the number and type of chromosomes present in the nucleus, not a photograph or diagram of them.

• Genome size is the total length of DNA in an organism. The examples of genome and chromosome number have been selected to allow points of interest to be raised.

• The two DNA molecules formed by DNA replication prior to cell division are considered to be sister chromatids until the splitting of the centromere at the start of anaphase. After this, they are individual chromosomes.

2. Developments in research follow improvements in techniques- autoradiography was used to establish the length of DNA molecules in chromosomes.

• Outline the advancement in knowledge gained from the development of autoradiography techniques.