3.14

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

chromosomes= genetic information in a cell

typical cell has a nucleus, within the nucleus there are a number of chromosomes depending on the species.

a chromosome is composed of d.n.a.

which forms a shape known as a double helix.

sections of this molecule are called genes. one chromosome may have up to 1000 genes.

each gene carries the information for the construction of a protein. the protein gives the characteristic associated with the gene for instance blood group.

so a gene controls the production of a protien, which controls the production of the characteristic of the cell.

different organisms have different numbers of chromosomes here are some examples:

cat=38. chicken=78. chimpanzee=42. human=46. chromosomes per cell.

chromosomes operate in pairs called homologous pairs.

homologous nature based on length of chromosome

on any homologous pair they have same gene but different variation in same area. (2 versions of each gene for one characteristic) a characteristic is an 'alleles'