The TYR gene codes for tyrosinase, an enzyme crucial for melanin production, affecting skin, eye, and hair colour.

Two copies of the recessive allele of the TYR gene can lead to albinism, characterised by a lack of the tyrosinase enzyme and thus a lack of melanin.

Albinism also often results in poor vision, rapid eye movements, and light sensitivity due to the lack of melanin.

The HBB gene codes for the β-globin polypeptide in haemoglobin. 

Mutations in this gene can cause sickle cell anaemia.

A mutation in the HBB gene can result in a less soluble form of haemoglobin being produced. The molecules group together in red blood cells forming long fibres, distorting red blood cells into a sickle shape and impairing oxygen transport.

A person with one copy of the sickle cell allele will have some normal haemoglobin and some sickle cell haemoglobin.

The F8 gene codes for coagulation factor VIII, which is essential for normal blood clotting.

Mutations in the F8 gene can lead to abnormal versions of the factor VIII protein being produced, so blood does not clot normally, causing excessive bleeding.

This disorder is called haemophilia.

The HTT gene codes for the huntingtin protein, which is involved in neurone development.

Huntington's disease is caused by mutations with excessive CAG repeats in the HTT gene.

There is a 50% chance of inheriting Huntington's disease if one parent carries the faulty allele.

This is because the faulty allele is dominant, so even if only one copy is inherited the person will develop Huntington's disease.

The Le gene affects the height of pea plants through the production of gibberellin.

The dominant Le allele in pea plants leads to tall growth by regulating gibberellin synthesis.

Plants that are homozygous for the recessive le allele produce a non-functional enzyme so do not produce the active form of gibberellin. This means that they remain short.

Genes code for proteins that can influence an organism's phenotype, their physical traits.