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Relationship between genes, alleles and chromosomes

Hi, I’m a little confused about how to answer questions about the relationship between DNA, genes, alleles, chromosomes and mutations. Thank you

Hi sealbanana101

That’s a very good question to ask, and one you need to understand. It comes up very often in exam questions as well!

So lets start with DNA.
This is your genetic material that’s found inside the nucleus of every living organism.
(Now, if you have done a DNA extraction experiment at school before, it will look like mush/snot !, if you haven’t don’t worry)
DNA are essentially long strands of molecules (made up of 3 key subunits - ribose, phosphate and a base)

Inside cells, DNA gets “organised” into very long strands of chromosomes.
(You have 46 chromosomes in every cell in your body - or rather, 23 homologous pairs of chromosomes)

A section of DNA can sometimes code for a gene. So in one chromosome, there can be hundreds to thousands of genes. (Just try to imagine how many genes you can have in all 46 chromosomes !)
(There are sections of DNA that just don’t code for anything!)

The “code” from the gene is actually a code for a sequence of amino acids which gets made into proteins.
Proteins often have some chemical function in your body, and is responsible for giving you certain traits. (Eg - hair colour, or eye colour )

Very simplistically put - 1 gene codes for a sequence of amino acids, which codes for a protein, and that specific protein is responsible for a “trait”.

Alleles are alternate forms of the same genes.
Since chromosomes comes in homologous pairs, there will always be at least 2 versions of any gene (for a particular trait). These “versions” are known as alleles.
It is easier to think of it like this: Everyone has the gene for eye colour, however, different people will have different alleles for eye colour. For example if you have brown eyes, you will have the allele for brown eyes, while someone who has blue eyes has the alleles for blue eyes. BUT you both will have the gene for eye colour.
[More on this will be covered in inheritance where you look at dominant and recessive alleles]

Lastly, mutations are a permanent change in the DNA (or genetic material). This can happen in either the somatic or gametic cells.
If a mutation happens in the somatic cell, it is not heritable, while, if it happens in the gametic cell (it can be heritable)

There are some helpful videos and notes on this website:

Hope that helps !!

Thank you, this is very helpful