B2(iii) - Genetics 8.

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Genetic Disorders.

Defective genes can cause serious problems:

Cystic Fibrosis is Caused by a Recessive Allele.

Cystic fibrosis is a genetic disorder of the cell membranes. It results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas.

1) The allele which causes cystic fibrosis is a recessive allele, f carried by about 1 in 30 people.

2) Because it's recessive, people with only one copy of the allele won't have the disorder, they're known as carriers.

3) For a child to have the disorder, both parents must be either carriers or sufferers.

4) As the diagram shows there's a 1 in 4 chance of a child having the disease if both parents are carriers.

Huntington's is Caused by a Dominant Allele.

1) Huntington's is a genetic disorder of the nervous system that's really horrible. Resulting in shaking, erratic body movements and eventually severe mental deterioration.

1) The disorder is caused by a dominant allele, N and so can be inherited if just one parent carriers the defective gene.



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