Genotype and Phenotype
Genotype are your genes
Phenotype is the physical expression of those genes
If we look at the gene for eye colour, we know there are multiple different variants called alleles.
For example your Gene for eye colour from your parents might be the allele for blue eyes from dad and the allele brown eyes from mum. This is your genotype
Whilst your eyes are brown. So, the physical expression of these two alleles results in you physically having brown eyes. This is your phenotype
The genotype is blue from dad, Brown from mum. Or, blue, Brown. Or simply bB
The phenotype is the physical expression of that gene: Brown Eyes
For every Gene, you have 2 Alleles
One from mum and one from dad
These Alleles might be the same: Homozygous
These Alleles might be different: Heterozygous
If they are different, the function of one might hide the function of the other
The one that is 'hidden' is: Recessive
The one that 'does the job' is: Dominant
Truck Genes
Before reading the following textbox, first have a look at the 'Truck Genes' illustration below and have a think about what is happening. What is it trying to show you?
Then, come back up and have a read of my explanation of my illustration
Chromosomes 1. Gene: Crane Truck.
The image below has 3 sets of chromosomes. There is a gene of interest on two of them
The first gene of interest is the Gene for Crane Truck. There are two versions as their are two chromosome 1's. One from each parent
Looking carefully you can see that the two versions of the Truck gene, we can see that the code is identical: 'Great Lego Sets'.
So the two alleles of the one gene are the same, or Homozygous.
They are both copied by RNA polymerase (the photocopier) and sent to the Endoplasmic Reticulum where the Ribosomes build them.
In the end there are two identical Crane Trucks
The Genotype is Truck (T), Truck (T). The Genotype can be simplified to: TT
The Phenotype, or physical expression, is two exactly the same crane trucks.
The Phenotype is 'Crane Truck'
Side note, the truck crane holds the microphone that I use for my lectures :-)
Genotype: TT (Homozygous Dominant)
Phenotype: Crane Truck
Chromosome 3. Gene: Bucket Truck.
The next gene of interest is for the Bucket truck
This gene is on Chromosome 3.
Their are two Chromosome 3's. One from mum and one from dad.
Looking at the Gene for Bucket truck, you can see that their are two versions, or alleles, and they are different.
On the chromosome from mum we got the allele 'ego' and on the chromosome from dad we got the allele 'lego'
These two alleles are both transcribed by RNA polymerase (copied by the photocopier). However, look at the Messenger RNA - there is a difference! a part is missing!
These copies are sent to the Endoplasmic Reticulum where the ribosomes then translate the message and build the truck. Notice a difference between the two?
Because of the difference between the two alleles, and then their mRNAs. The end proteins are different. One protein has the Bucket, the other one does not
However, because there is one truck that can do the 'Bucket' functions, it doesn't matter too much that the other one cant. Rather production of the one that can will be ramped up and more of that one will be made. Because of this the Bucket one will do the job and be Dominant. The no-bucket truck can not do the job and will be hidden away as a Recessive allele
The Genotype was Heterozygous as the alleles were different: Bucket 'B' and no-bucket 'b': Bb
The Phenotype was "Bucket Truck" as there was still Bucket Truck proteins doing the Bucket Truck function so the non bucket truck was hidden.
Genotype: Bb (Heterozygous)
Phenotype: Bucket Truck
Mr Cowley Lectures on Genes, Alleles and Proteins
YouTube explanations of Genes and Alleles, Homozygous and Heterozygous Alleles, and Dominant and Recessive Alleles
A bit quicker than my lectures :-)
The next page explains how different alleles for the same gene come into existence