Genetic inheritance
26 Nov
How are genetic conditions inherited?
Each cell in the human body has 23 pairs of chromosomes, with one chromosome from each of the 23 pairs inherited from the father and one inherited from the mother. The chromosomes contain all the genetic information for that individual person and the information is contained in the genes.
Genes are the reason that we inherit characteristics from our parents, for example our hair colour or the colour of our eyes, a highly interesting topic in the area of medical genetics. Sometimes, there are different forms of genes, known as alleles and this is the case when parents have different colour eyes; for example, if one parent has blue eyes and one parent has brown eyes, this means that their child will end up with a brown allele and a blue allele. As brown alleles are dominant, the child will have brown eyes. The blue allele is recessive, which means that a child must inherit a blue allele from both parents to have blue eyes.
Medical genetic conditions can also be passed on through families, which occur when a genetic mutation is passed on from parents to child. Whether or not a child will inherit a genetic condition depends on two factors: whether the gene for the specific condition is dominant or recessive and which genes the child inherits from their parents.
Recessive inheritance
Recessive inheritance means that a child must inherit two copies of a specific gene to have a genetic condition, which means that both parents must have a copy of the mutated or abnormal gene and are therefore carriers. If the child only inherits one copy of the faulty gene, they will be a carrier of the disease but if they inherited two copies of the gene they will have the condition. If both parents carry a copy of a faulty gene, there is a 25 percent chance that their child will suffer from the condition. An example of a recessive condition is cystic fibrosis and if a child suffers from cystic fibrosis, this means that they have inherited a copy of the faulty gene from both of their parents.
Dominant inheritance
Dominant inheritance means that a child must only inherit one copy of a faulty gene to suffer from a dominant condition and if one of the parents has a copy of the faulty gene, there is a 50 percent chance that it will be passed on to their child. Type 1 neurofibromatosis is an example of a dominant condition, which can be passed on if either the father or the mother has a copy of the abnormal gene.
