Genetic Disorders

Inherited Disorders

Some disorders are inherited, such as:

• red-green colour blindness
• sickle cell anaemia
• cystic fibrosis.

Inherited disorders are caused by faulty genes, which are mostly (but not always) recessive alleles. For example, cystic fibrosis is an inherited disorder that affects the cell membranes, causing the production of thick and sticky mucus. It is caused by a recessive allele, which means that it must be inherited from both parents.

Genetic Testing

Scientists are now able to test adults and unborn babies for alleles that can cause genetic disorders. However, the scientific information produced raises many issues that science cannot address. For example, should a couple with a one in four risk of having a child with cystic fibrosis take the gamble, or decide not to have any children at all? If a woman becomes pregnant with a child that is going to have cystic fibrosis, should she have the child, or choose to have an abortion? These are questions about values that science cannot answer. Different people will have different views.

Genetic diagrams are used to show the possible outcomes of a particular cross. A dominant allele is shown by a capital letter, and a recessive allele by a lower case letter.

Cystic Fibrosis

Cystic fibrosis is an inherited disorder caused by a recessive allele. This genetic diagram shows the possible outcomes when both parents are heterozygous for the faulty allele. There is a one in four chance of the offspring being homozygous for the faulty allele, and so having cystic fibrosis.

This genetic diagram shows the possible outcomes when both parents carries the faulty allele.

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