Genetic variants in non-coding DNA can influence phenotype | Biology

Starter quiz

Match each word to its correct meaning.

mutagen

⇔

Something capable of causing a change in the genetic code. ✓

mutation

⇔

A change in the genetic code. ✓

transcription

⇔

The process of copying a gene and making mRNA. ✓

translation

⇔

Using the genetic code of mRNA to make a polypeptide. ✓
Match the number to the description.

four

⇔

The number of types of nucleotide base in DNA. ✓

two

⇔

The number of nucleic acid strands in a molecule of DNA. ✓

one

⇔

The number of nucleic acid strands in a molecule of mRNA. ✓

three

⇔

The number of nucleotide bases in a triplet code. ✓
Which of these is not a type of mutation?

deletion

division ✓

insertion

substitution
Allele 1 has mutated to become allele 2. Allele 1 code: ATT CCG GAC TAT ATA CGC CCC. Allele 2 code: ATT CGG GAC TAT TAT ACG CCC C. How many mutations have there been in allele 1

'2' ✓
Put the statements in order to describe how a gene in the nucleus is used to make an enzyme that controls a chemical reaction in the cytoplasm.

1

⇔

A gene copy called mRNA is made in the nucleus.

2

⇔

The copy is small enough to get into the cytoplasm.

3

⇔

The sequence of bases in mRNA is read at a ribosome.

4

⇔

Amino acids are assembled into a sequence determined by the mRNA base sequence.

5

⇔

The amino acid sequence determines the 3D shape of the enzyme.
A change in the 3D structure of a protein may lead to a change in an organism such as a different eye colour. What word do biologists use for physical characteristics such as eye colour?

'Phenotype' ✓

Exit quiz

Genes are instructions to a cell on how to produce which type of molecule?

amino acids

mRNA

nucleotides

proteins ✓
DNA that isn’t used to determine the structure of a protein is called ______ DNA.

'non-coding' ✓
What does the term 'gene expression' mean?

A gene codes for a protein using a nucleotide sequence.

A gene is activated so that the protein it codes for is produced. ✓

RNA polymerase binds to the non-coding DNA before a gene.

The protein coded for by a gene is produced.
Put the events in the synthesis of a protein in the correct order.

1

⇔

A section of non-coding DNA activates a gene.

2

⇔

RNA-polymerase enzyme binds to a section of non-coding DNA before the gene.

3

⇔

mRNA copy of the gene is made.

4

⇔

mRNA copy of the gene attaches to a ribosome and translation occurs.

5

⇔

Amino acids join together in an order determined by the mRNA to form a protein.
Changes to the non-coding DNA nucleotide sequence can happen due to copying errors or because of environmental factors such as chemicals in cigarette smoke. What are these changes to the DNA called?

'Mutations' ✓
There are several ways changes to non-coding DNA can affect an organism's phenotype. Match the change to the description of how it can alter phenotype.

Cell division genes are always activated

⇔

Cells constantly grow and divide leading to tumour formation. ✓

Binding of RNA-polymerase is prevented.

⇔

Transcription is prevented and the protein can’t be produced. ✓

The activation of a gene is prevented.

⇔

Gene remains inactive and protein is not produced. ✓

Worksheet

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Lesson Details

Key learning points

When a cell copies a gene to make mRNA (the instructions to make a protein), this is called gene expression.
Only around 1-2% of the genome is genes; the rest contains code that controls gene expression.
A genetic variant in a non-gene (so called "non-coding") section of the genome can affect gene expression.
Non-coding DNA affects gene expression because it is where RNA polymerase starts copying the gene for protein synthesis.
Genetic variants in non-coding DNA can impact gene expression and therefore an organism’s phenotype.

Common misconception

All DNA is genes that code for proteins; and that our characteristics are only affected by our genes

Most of the DNA is non-coding (non-genes), and controls when genes are expressed (i.e. when proteins are made). Changes (genetic variants) in non-coding DNA can affect characteristics (phenotype) as they control whether a gene is expressed or not.

Keywords

Gene - A section of DNA that holds the genetic code for a protein.
Protein - A chemical substance whose structure is coded for by the genetic code in genes.
Gene expression - The process in which genes are copied during the first step in protein synthesis.
Genetic variant - Produced when a mutation causes a change in the genetic sequence of a gene or non-coding section of DNA.
Phenotype - The physical characteristics of an organism.