Genetic variants in genes can influence phenotype | Biology

Starter quiz

Match each of the following to the correct number.

1

⇔

the number of amino acids coded for by each triplet of bases ✓

2

⇔

the number of nucleic acid strands in a DNA molecule ✓

3

⇔

the number of nucleotide bases in one triplet code ✓

4

⇔

the number of different nucleotide bases found in DNA ✓
If a single nucleotide base in DNA is swapped for another one, this is called a substitution ______.

'mutation' ✓
What is the cause of most mutations in DNA?

chemical mutations in cigarette smoke

errors in copying DNA when cells divide ✓

high-energy ultraviolet radiation

X-ray radiation
This is part of a genetic code: TAC CAG TCA CAG. A mutation changes the code to TAC CAG TCC AG. What kind of mutation has taken place?

'deletion' ✓
Insertion mutations have a greater effect on the genetic code than substitution mutations. Why?

Insertion mutations remove a base from a triplet code.

Insertion mutations add a base to a triplet code. ✓

Insertion mutations change every triplet code before the mutation.

Insertion mutations change every triplet code after the mutation. ✓

Insertion mutations swap one base for another in a triplet code.
In which type of cell would a mutation have to happen if the mutation was to be inherited by a person’s offspring?

gamete cell ✓

nerve cell

red blood cell

root hair cell

Exit quiz

Which word means the physical characteristics of an organism?

genome

phenotype ✓

polymer

ribosome

transcription
A different version of a gene, created by a mutation, is called an ______.

'allele' ✓
Match each word to its correct definition.

gene

⇔

a section of DNA that holds the genetic code for a protein ✓

genetic variant

⇔

a section of DNA in which a mutation has changed the base sequence ✓

allele

⇔

a different version of a gene, created by a mutation ✓

triplet code

⇔

a set of three nucleotide bases that codes for one amino acid ✓
Match each mutation to the change it would cause in the amino acid sequence of the protein coded for by a gene.

GAT mutated to GGT

⇔

would change leucine to proline ✓

CAT mutated to CAA

⇔

no change in amino acid ✓

CAC mutated to GAC

⇔

would change valine to leucine ✓

CAA mutated to GGA

⇔

would change valine to proline ✓
Put the steps in the correct order to describe how a mutation in a gene can change an organism’s phenotype.

1

⇔

A mutation changes the sequence of bases in a gene.

2

⇔

The gene is transcribed to make mRNA.

3

⇔

Translation takes place at a ribosome, when tRNA joins amino acids together.

4

⇔

The amino acid chain folds to make a protein.

5

⇔

The protein folds differently because one or more amino acids has been changed.

6

⇔

The protein structure is changed, so it might not work properly.
Who identifies a mutation that is the most likely to result in a non-functional protein?

Izzy: “A substitution mutation in a gene.”

Jun: “A deletion mutation in a gene.” ✓

Sam: “A substitution mutation in non-coding DNA.”

Sofia: “A mutagen in a gene.”

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Lesson Details

Key learning points

When a mutation changes the sequence of nucleotide bases in a gene, this creates a genetic variant of the gene.
If a triplet code in a gene is changed, this may or may not change the amino acid sequence in the protein that is made.
A change in the amino acid sequence of a protein can change the 3D shape of the protein.
A change in the 3D shape of a protein can change what it does (e.g. by changing the shape of an enzyme’s active site).
These changes can have impacts on an organism’s phenotype.

Common misconception

Mutations always have a negative effect on an organism.

Mutations can produce variation in a phenotype by producing alleles of a gene.

Keywords

Gene - A gene is a section of DNA that holds the genetic code for a protein.
Genetic variant - A genetic variant is produced when a mutation causes a change in the genetic sequence of a gene or non-coding DNA.
Allele - A genetic variant in a gene creates an allele (a different version of the gene), which produces a different phenotype.
Triplet code - The triplet code is carried by genes. Each three nucleotide bases codes for a specific amino acid.
Phenotype - The phenotype is the physical characteristics of an organism.