Genetic diagrams and pedigree analysis

Genetic diagrams and pedigree analysis

Human body cells have 23 pairs of chromosomes in the nucleus.

The cell’s nucleus contains chromosomes. These are long threads of DNA, each made up of many genes.

Codominance

Some alleles are both expressed in the same phenotype, a situation called codominance.

There are three possible genotypes: WW, BB and BW.

Blood groups

The gene controlling human ABO blood groups has three alleles, not just two:

• IA and IB are not dominant over one another
• both are dominant over IO

For humans to reproduce, fertilisation needs to happen. Gametes are produced by meiosis. As a result of this type of cell division, each…