👪 Family trees (pedigree)

This type of diagram shows genetic inheritance over generations. Squares are males and circles are females. Filled shapes are affected by the specified condition while hollow shapes are not.


Shapes joined horizontally are couples while shapes joined vertically are children; those joined indirectly are siblings. These are purely genetic relationships of surviving individuals (other symbols are used for anyone adopted, miscarriages, etc.). For example, in the above diagram the father (generation I) has a genetic condition. Together with the mother, they have 1 daughter and 2 sons. All but 1 son also have the condition.

They are generation II. Of them, the son with the condition goes on to have children with an unaffected female. They have two daughters. One inherits the condition. This is generation III.



Mutations are a random occurrence during DNA replication and the rate of mutation is influenced by external factors such as UV radiation. Mutation occurs spontaneously.

There are different types of mutation:


1. Deletion where one or more nucleotide bases are deleted. AGTCA becomes AGCA

2. Substitution where one or more nucleotide bases are replaced by others. AGTCA becomes AGTCG



3. Addition where one or more nucleotide bases are added as extra. AGTCA becomes ATGTCA

4. Inversion where a section of DNA is…