Single gene disorders - Autosomal dominant inheritance
Any sufferers from autosomal dominant conditions only require one dominant allele so can be either homozygous dominant or heterozygous. This affects both genders equally.
An example of an autosomal dominant inherited diseases is An inherited disease of the brain that causes damage to certain brain cells..
Huntington鈥檚 disease is an inherited disorder that causes damage to certain brain cells. It is caused by a An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.. In a genetic diagram:
- the Alternative form of a gene that is expressed only if a dominant allele of that gene is not present. An organism must have two copies of a recessive allele for that allele to be expressed. can be shown as h
- the dominant allele can be shown as H
Someone who is homozygous (HH) or heterozygous (Hh) for the dominant allele will develop Huntington鈥檚 disease.
In example 1, the mother carries one copy of the Huntington鈥檚 allele and has the disease. The father does not carry the Huntington鈥檚 allele, so he does not have the disease. The chance of them producing a child with Huntington鈥檚 disease is 2 in 4, or 50%.
In example 2, both parents have one dominant allele and one recessive allele. This means that they are This describes a genotype in which the two alleles for a particular characteristic are different. for that particular gene. The chance of them producing a child with Huntington鈥檚 disease is 3 in 4, or 75%.
In example 3, the mother is heterozygous. The father is This describes a genotype in which the two alleles for the characteristic are identical. because he has two identical alleles for that particular gene. The chance of them producing a child with Huntington鈥檚 disease is 4 in 4, or 100%.
Half the possible offspring will be homozygous, HH, and half will be heterozygous, Hh. The ratio of HH to Hh is 1:1 or 50%.