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Watch this, it is a really good explanation of mutations and their consequences
Mutations are changes in the DNA sequence
These can be single letters or larger
These can cause a protein to be shaped differently, affecting the function of the protein
A change in the function of the protein can result in organism level implications
These can be bad, leading to disability
These can also be good, leading to evolution!
The Truck Genes example from the previous page provides a good example of a mutation
Lets look at Chromosome 3
We have the Gene for "Bucket truck"
There are two versions of the gene, one from mum and one from dad
Look closely at the two versions
One is "LEGO"
The other is "EGO"
This is a point deletion of the letter L.
This one letter change is called a point mutation. It is a change in the spelling of the gene
Because of this difference in spelling the instructions that are sent as messenger RNA's are different. Have a close look at the two images called "messenger DNA", do you see the difference?
Because this one part is missing (the arm that lifts the bucket) the bucket truck protein has a different shape. It has no bucket.
Because its shape is different, so too is its function - it can not carry things in its bucket
This is an example of a single letter change in the gene (allele) resulting in the protein being different
These differences in the spelling of a gene is the reason that there are different alleles - such as the Bucket truck gene having the alleles B = bucket and b = no bucket
Usually the gene will have hundreds or thousands of letters, but even so, one letter difference can result in a different protein being made
The point deletion of the "L" for the instructions for the "Bucket truck" had a significant impact on the overall structure and thus function of the truck. You can see why when looking at the Messenger RNA, the message is different, and thus the instructions are different
It is odd that the deletion of just one letter can have such a huge impact
Luckily most mutations are 'substitution point mutations' rather than deletions. This means that the letter is simply switched with another letter. As the amino acid might have several three letter codes that code for it, a simple letter swap might still result in the same amino acid and so it has no impact on the protein ("silent mutations). So instead of "LEGO" it is swapped with "ZEGO" and the truck might still get all of its parts, the structure will thus be Bucket Truck, and so the function will be Bucket truck. A Silent mutation like this will not change the Genotype either as you don't know about the mutation as there is no consequence, no physical manifestations, no loss or gain of function of the protein. So in the case where a person has LEGO and ZEGO for their alleles, the genotype will be BB.
However, a substitution might have an impact. For if LEGO becomes KEGO then perhaps then a circle wheel is swapped for a square. This does impact the shape of the truck. If the truck wheel shape is changed, and thus the overall image of the truck, then the 'bucket truck' will not function as well as it should. Thus this deficit could have a detectable consequence.
As KEGO is a 'reduction of function' mutation, it will probably be given a little letter so b
Hopefully though the truck company has the instructions for the other truck, LEGO. So it will up production of the LEGO truck, B, and this functional "Bucket truck" will make up for, dominate, and hide the recessive, less effective 'b' KEGO Bucket truck. This is the advantage of being Heterozygous - one of the wins for 'sexual reproduction'
If the company is homozygous recessive for KEGO, bb, then they are in trouble. But, probably not as much trouble as the company that is homozygous recessive for the 'EGO' mutation!!
I wonder what advantages there are for the company that is homozygous dominant for LEGO, LEGO?
Have a watch of a minimum of 3 mutations clips to the side here and below. They are all really good :-)
We look at mutations as being only bad
But what if you were stuck with that bad bucket truck
Its a bucket truck with no bucket, so that is bad .. right??
Well probably, but lets look at the carrying function of the bucket truck
Lets change the structure of the truck through a mutation. LEGO becomes EGO. The structure of the truck changes, so it follows that its function will also change. Structure = Function.
Lets look at the carrying function of of the truck now
Well, looking at the photos, it appears that the truck is actually better at carrying without the bucket
In this case, the change in structure due to this mutation has enhanced its function
This can still be bad - perhaps this will result in too many cups in the destination
However, what if it is good? What if it benefits the organism?
The way that nature determines if something is of benefit to an organism is by the number of its offspring that survive to have their own offspring.
If a mutation is of benefit, then that will result in the organism having more grandchildren
That is an oversimplification of the truth, but it is a truth nonetheless
Whenever an organism does not reproduce, they are then the end of their lineage. If they have siblings that go on to have offspring, then their parents and their siblings' lineage continues, but their unique genetic combination does not.
Think of two brothers on a deserted island competing for the same girl; she ultimately chooses one, and they have children, thus his overall genotype resulted in a phenotype that she liked more than the other guy's phenotype (and thus his genotype). The more successful guys' alleles are passed on, and the non-successful guys' alleles will not.
A bad mutation may result in the organism not having any offspring, or having only a few offspring
A good mutation may result in the organism having many offspring and many descendants
This is Natural Selection
If that 'b' allele, for the bucket-less truck, is an advantage, then those that have 'b,b' as their genotype will have more offspring. These offspring will spread these 'b' alleles through the population. More 'b,b' and 'B,b' descendents will exist. The 'b,b's will still outbreed the 'B,b's until that 'B' allele is pushed out and the new normal for that gene is 'b'
Point Mutations
Point Mutations
Point mutations are single-letter mutations - ATCG - so either a nucleotide is swapped for another one (substitution) or a letter is randomly inserted (insertion), or randomly deleted (deletion)
Substitution (Swapping a Letter)
Substitution (Swapping a Letter)
This is a typo where one letter is swapped for another.
Silent Mutation: The meaning of the sentence remains unchanged. THE FAT CAT ATE THA RAT Even though the word "THE" has been changed to "THA", the overall meaning of the sentence is still perfectly understood. This is exactly like a silent mutation, where a change in a DNA codon still results in the same amino acid, leaving the final protein's function unchanged.
Missense Mutation: The meaning of one word changes, altering the sentence. THE FAT HAT ATE THE RAT 🎩 Swapping "C" for "H" changes "CAT" to "HAT". The sentence is still readable, but its meaning is now completely different. This is like a mutation that codes for a different amino acid, which alters the final protein's shape and function.
Nonsense Mutation: The sentence is cut short. THE FAT CAT ATE THE .AT 🛑 Swapping "R" for a "STOP" signal (a period) ends the sentence prematurely. The full message is never delivered. This is like a mutation that creates a "stop" codon, resulting in a shortened, truncated, incomplete protein that is usually non-functional.
Insertion & Deletion (Frameshift)
Insertion & Deletion (Frameshift)
This is when a letter is added or removed, which shifts the three-letter reading frame and scrambles the rest of the message.
Deletion: If we remove the "F" from "FAT": THE ATC ATA TET HER AT... ⛓️ Every word after the deletion is now unreadable gibberish.
Insertion: If we add an "X" after "FAT": THE FAT XCA TAT ETH ERA T... ⛓️ Similarly, every word after the insertion is scrambled.
This is why frameshift mutations are often so disruptive—they don't just alter one word, they corrupt the entire rest of the genetic sentence.
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