Chromosomes are large molecules of DNA (deoxyribonucleic acid). This DNA has a double helix structure and is composed of genes.

HIGHER TIER:

• Each gene provides the coding for a specific combination of amino acids which then produces a particular protein.

NOTE: You don’t need to know the names of the four bases or how complementary pairs of bases allow the replication of DNA to occur.

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Genetic disorders

Genetic disorders are diseases that are passed onto the offspring by one or both of parents. They’re caused by gene mutations. There are a number of genetic disorders.

Polydactyl

In this condition an individual is born with additional fingers or toes. It’s caused by the dominant allele of a gene which means that only one parent has to be the carrier for the characteristic to show itself in the offspring.

Cystic Fibrosis

This disorder affects cell membranes mainly in the lungs, liver, pancreas, sinuses, intestines and sex organs. The mucus produced by a sufferer is very thick and sticky and can easily clog up the lungs. It’s caused by a recessive allele which means that both parents need to be carriers. However, neither of them actually has to have the disease because they could both carry a recessive and dominant allele.