Monday, June 22, 2009

[Science Form 4] Genes

The human body is made up of cells, and in every cell, there is a nucleus that contains chromosomes.

Genes in the chromosomes provide instructions for cell growth and function.

Specific genes also determine hereditary traits in an individual.

Eg: There is a gene for hair colour and a gene for eye colour. Variations of a specific gene are called alleles.

During sexual reproduction, the genes for certain traits are passed down from parents to their offspring.

A child the carries two genes for each trait - one from the father's sperm and the other from the mother's ovum.

The genes can either be dominant or recessive. If the child inherits one dominant gene and one recessive gene, the dominant will overpower the recessive.

Eg: Given that T represents a father's dominant height gene and t represents a mother's recessive height gene, their child whose height gene is represented by TT or Tt will be tall. On the othe hand, their child whose height gene is represented by tt will be short.

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