3.14 Chromosomes

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

1. What are chromosomes, and what are they made of?
Chromosomes are Genetic information contained within the nucleus of a cell

Here you can see a pair of human chromosomes

Chromosomes are composed of a molecule known as DNA (Deoxyribonucleic acid), this DNA forms a shape known as the double helix [indicated in yellow in the above picture]

Sections of this DNA molecule are called Genes [see 3.15], one chromosome will have 1000’s of genes. Each gene carries the information for the construction of a Protein [see 3.16] the protein controls the characteristics associated with the gene (e.g. blood group)

DNA (Gene) -> Protein -> Characteristic

2. How many chromosomes?

Different organisms all have a different number of chromosomes
For example: a Cat has 38, a Chicken 78, a Chimp 42 and Humans have 46

3. Genes operate in pairs known as homologous pairs

This diagram illustrates some of the homologous pairs within an organism

Their Homologous nature and pairing is based upon the equal length of the chromosomes

If a gene is selected from one of the chromosomes in a homologous pair, its gene loci (position at which it is located in the chromosome) is the same in the pairing chromosome.

In a pair of chromosomes there are 2 versions of the same gene for one characteristic, one found in each chromosome but at the same gene loci. These versions are called Alleles.