Flashcards · Biology · DNA and Protein Synthesis
Genetic Variants and Their Effects (Higher tier)
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What is a genetic variant?
A difference in the base sequence of DNA between individuals.
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What causes a genetic variant?
A mutation.
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What is a substitution?
One base swapped for a different base.
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What is a frameshift?
An insertion or deletion that changes how all of the following triplets are read.
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How can a variant in non-coding DNA change the phenotype?
It changes how well RNA polymerase binds, so the amount of protein made changes.
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Does a non-coding variant change the protein itself?
No. It changes the quantity of the protein, not its structure.
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How can a variant in coding DNA change the phenotype?
It changes the amino acids, so the protein's shape and activity change.
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Why might a substitution have no effect on a protein?
Several triplets code for the same amino acid, so the amino acid may not change.
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What is the cause of sickle cell disease?
A single base change in the haemoglobin gene, so valine replaces glutamic acid.
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What happens to red blood cells in sickle cell disease?
They are distorted into a sickle shape at low oxygen levels.
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Give an example of a variant in non-coding DNA.
Lactase persistence, where a variant near the gene keeps it switched on in adults.
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What does a stop codon in the wrong place do?
It cuts the polypeptide short, so it usually does not work.
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What happens if exactly three bases are deleted?
One amino acid is lost, but the rest of the triplets are read correctly.
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Do all variants change the phenotype?
No. Many have no effect on it.
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A variant makes RNA polymerase bind more strongly. What is the effect?
More mRNA is made, so more protein is produced.