Genetic conditions
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 geneThe basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production. or in the number of chromosome Genetic structures that usually occur in functional pairs in the nucleus of cells (except gametes and bacteria)..
Haemophilia
- Sufferers are unable to clotA clump of platelets and blood cells that forms when a blood vessel is damaged. their blood resulting in excessive bleeding, even from small cuts or bruises.
- It is a sex-linked, inherited condition caused by a recessive An allele that will only show in the phenotype if there is no dominant allele present (i.e. when two recessive alleles are present). allele on the X chromosome.
- Sufferers are almost exclusively males because they only need one recessive allele.
- However, if their X chromosome carries the dominant normal allele, they 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 carrierSomeone who does not suffer from a condition but carries the allele and can pass it to his or her offspring.. Although they themselves are 'normal', they can pass the recessive allele to half of their children.
Cystic fibrosis
- Mainly affects the lungs and digestive system, which become clogged with mucusSlimy white protein, which lines the respiratory tract and alimentary canal. leading to frequent infections.
- It is caused by a recessive allele, which means only homozygousWhen the 2 alleles are the same (e.g. BB) recessive individuals (cc) will be affected.
Huntington’s disease
- 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.
Down syndrome
- 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.