3.14 Chromosomes

3.14 Recall that the nucleus of a cell contains chromosomes on which genes are located.

- Chromosomes are the genetic information within a cell. A typical cell would have a nucleus, and when we ipened that nucleus up we would find a number of chromosomes.

- The chromosome is composed of a molecule known as DNA, which forms a shape known as the double helix. Sections of this molecule are called genes, and one chromosome will have thosands of genes.

- Each gene carries the information for the construction of a protein (see 3.16). This protein gives us the characteristic associated with the gene (for example a blood group).

- Different organisms have different numbers of chromosomes. E.g. Cat = 38, Chicken = 78, Chimpanzee = 42, and a Human = 46.

- Chromosomes operate in pairs (homologous pairs). The diagram illustrates an example of some of the homologous pairs. Homologous nature is based on the length of the chromosomes.

This next diagram shows that if we locate a gene on any position on the chromosome. It will give us a position known as a "Gene Loci". If we go to the same position on the homologous pair we will find the same gene. So for instance we will two versions of each gene for one characteristic. These versions are called "Alleles" (covered in 3.17).