Alleles

So, remembering what is said about genes being made so they look for a certain type of protein, this is because they interact with different types of the same protein. A protein can be the same protein, but have an isotopeA variant of an element.. This is what an Allele is. So, in this example, the allele is a different version of the same gene. Because there are two copies of genes, one from each parent, it means we will have two alleles of each gene. They could both be the same allele or there could be two different alleles.

• If these two allele were the same, we would use the term homozygous. This means two of the same type.
• If these two allele were different, we would use the term heterozygous. This means two different types.

This is also where dominant and recessive genes come into play. For example, your parents are having a new baby. Currently, it's within the womb of the mother, and we don't know how big it will be, or what colour it's eyes are.

Now, fast forward to the baby being born, and it is born with blue eyes. It's only later in development that the eyes change colour. This is due to dominant and recessive genes. Your parents may have blue and brown eyes. In this example, the brown trait in your genes is the dominant gene. So, eventually at some point in the child's development, it will end up having brown eyes. This can take around 5 or 6 years to fully change, an actually, the brown may not be full on brown, and have tints of blue still.

If for instance, both parents had blue eyes, this would be called homozygous recessive, as both genes are recessive, but the same. The same is said for two parents who have brown eyes, except it's called heterozygous dominant. This is because they both have the dominant brown eye gene.

Genotype & Phenotype

At last, you have reached your destination. Please mind the gap when exiting the vehicle... Wait, hang on. I mean, we are at the point you need to be to be able to understand what these two are, so here's more:

A genotype is the entire collection of alleles that we have. So, in terms of the three examples above (heterozygous, homozygous recessive and homozygous dominant), they all have different genotypes as they each have different alleles.

Your phenotype is a collection of characteristics you get from your genotype, and are attributed to the physical appearance. So, for the examples above, if two babies looked the same (same eye colours, same facial features, etc) that means they would be classed as having the same phenotype, even though their genotypes may be different. Because a baby with blue eyes would be classed as homozygous recessive, this means it would look different, and therefore have a different genotype.

While I've used the examples of a human here, it goes for all multi-celled organisms. Animals and plants also have these traits that can change them as well.

Here is a YouTube video from Cognito on alleles, genotype and phenotype: