3.14 Chromosomes

Key Points:
1. The nucleus of a cell contains genes, and the genes are located in the chromosomes.
2. Chromosomes are the genetic information within a cell. In a normal cell, the nucleus would contain a number of chromosomes.
3. The photograph shows a single human chromosome. The chromosome is composed of DNA, which stands for Deoxyribonucleic acid, and this forms a shape known as the double helix. 
4. Sections of this molecule are called genes, one chromosome will have many genes eg. 1000
5. Each gene carries the information for the construction of a protein. The protein has a characteristic associated with the gene, eg. Blood group. 
6. Different organisms have different numbers of chromosomes. Cats have 38, Chickens have 78, and Humans have 46 chromosomes per cell.
7.  Chromosomes operate in pairs, homologous pairs. The next diagram shows the homologous pairs. The homologous nature is based on the length of the chromosomes. A gene located on a chromosome is called the gene loci. If you go to the same position on the other gene in the homologous pair, the same gene will be there. Basically 2 versions of each gene for one characteristic. These versions are called alleles.