Chromosomes

Skill: Use of databases to identify the locus of a human gene and its polypeptide product.  
​Aim 7: Use of databases to identify gene loci and protein products of genes.Use this link to find genes located on each chromosome individually.
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 (somatic cells).
• Haploid nuclei have one chromosome of each pair (sex cells).

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.
​• 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.
Application: Use of karyograms to deduce sex and diagnose Down syndrome in humans.  
​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.
The number of chromosomes is a characteristic feature of members of a species.
Application: Comparison of diploid chromosome numbers of 
Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum.

Application: Comparison of genome size in
T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica.
Application: Cairns’ technique for measuring the length of DNA molecules by autoradiography.
International-mindedness:
Sequencing of the rice genome involved cooperation between biologists in 10 countries.