Biology - B3

Inside the nucleus are chromosomes

Chromosome = 1000s of coils of genes

Genes = comprise ‘DNA’ that decides our characteristics

DNA = deoxyribose nucleic acid (chemical)

Each gene acts as a code for a particular characteristic

A human egg cell and sperm cell contains 23 chromosomes

Embryo therefore contains 23 pairs of chromosomes

Each pair contains a gene from your mother, and a gene from your father for a particular characteristic

So each pair contains two “options” for a characteristic

These options are called alleles e.g. gene = eye colour; alleles = blue eye colour, brown eye colour