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.