GENETICS AND INHERITANCE

In biology, the term inheritance refers to the passing on of characteristics or traits from parents to their offspring. Every living being inherits characteristics from its parents through genetic material (DNA/chromosomes) that is passed on through reproduction.

Think of it like this: When a baby is born, it receives some traits from its mother and some from its father. These traits can be anything from eye colour, hair texture or even susceptibility to certain diseases. In biology, we call this passing on of traits from one generation to the next genetics.

Studying inheritance helps us to understand how traits are passed on, how they differ from individual to individual and how new traits can arise through the process of evolution.

A distinction is made between different types of inheritance, which are explained in more detail below. 

In recessive inheritance, a correct version of the gene prevents the disease from manifesting, i.e. two defective genes are required for the disease to manifest. For an autosomal recessive disease to occur, a child must inherit two mutated or defective copies of the gene (two gene alleles), one from each parent. If only one mutated or defective allele is inherited, the child does not have the disease but is a carrier of the disease/mutation. In a family in which both parents are carriers of the mutation, there is a 25% risk of the parents' children also developing the disease. Both sexes are equally affected.
Examples for autosomal recessive inheritance are diseases such as Bardet-Biedl syndrome, primary hyperoxaluria type 1 or autosomal recessive polycystic kidney disease (ARPKD).

In dominant inheritance, one copy of the defective gene is sufficient to trigger the symptoms of the disease. This means that if a gene is inherited dominantly from the parents, around 50 % of the offspring will also be affected.

For example, in autosomal dominant inheritance, if a child receives one normal and one abnormal gene from the parents and the abnormal gene is dominant, it will overwhelm the normal gene. As a result, the possession of a single abnormal gene is sufficient to develop the disease. This phenomenon is observed in diseases such as Marfan syndrome, neurofibromatosis type 1 and HNF1B nephropathy.

Digenic inheritance means that a mutation in two different genes causes a characteristic or a disease. It's like having two keys that need to be turned at the same time to open a door. In this case, both mutated genes must be present for the condition or disease to appear. If only one of the genes is mutated, the condition or disease may not be noticed, as both mutations must be active. This type of inheritance is even more complex as it involves interactions between two different genes and not just one.