Some genetic conditions are inherited – passed from parent to child.
Genetic conditions are caused by mutations.
Mutations are random changes in the structure of a gene or in the number of chromosomes.
- Sufferers are unable to clot their blood resulting in excessive bleeding, even from small cuts or bruises.
- It is a sex-linked, inherited condition caused by a recessive allele on the X chromosome.
- Sufferers are almost exclusively males because they only need one recessive allele.
- However, if his X chromosome carries the dominant normal allele, he will be normal.
- Females with two normal alleles will also be normal.
- Only in the rare case of a female having two recessive alleles will they show the condition.
- Those women with one normal and one recessive allele are called carriers. Although they themselves are normal, they can pass the recessive allele to half of their children.
- Mainly affects the lungs and digestive system, which become clogged with mucus leading to frequent infections.
- It is caused by a recessive allele, which means only homozygous recessive individuals (cc) will be affected.
- Affects nerve cells in the brain, leading to brain damage.
- It usually becomes apparent in middle age.
- There is no cure and it is eventually fatal.
- This condition is caused by the presence of one dominant allele.
- Individuals have reduced muscle tone and cognitive development.
- It is caused by the presence of an extra chromosome – a sperm cell with 23 chromosomes fertilises an egg cell with 24 chromosomes.
- This results in an individual with 47 chromosomes rather than the ‘normal’ 46.
- An individual with Down syndrome has three copies of the 21st chromosome rather than two.