Genetic variation in disease Flashcards
What is an allele?
Alternative forms of gene/locus/variant
What is homozygous?
Two copies of same allele at same locus
What is heterozygous?
Different alleles at same locus
How is DNA replicated?
RNA polymerase attaches to start of gene when switched on to make mRNA
mRNA to cytoplasm
Ribosomes bind, read code and produce chain of amino acids carried by tRNA
What is a single base substitution?
Replacement of one nucleotide with another
What is a silent mutation?
No change to amino acid sequence or function, doesn’t cause disease
Silent mutation: doesn’t alter polypeptide product of gene - often single base-pair substitution at third position in codon, degeneracy of genetic code, no alteration in protein
What is a non-synonymous mutation?
Changes amino acid sequence, structure of protein, causes disease
Function of stop codons
Premature termination of translation of polypeptide chain
Expression of truncated protein but mRNA usually degraded by nonsense-mediated decay so no protein is made
What is missense?
Coding for different amino acid
Non-conservative mutation
new amino acid is chemically dissimilar
Conservative mutation
Replacement of amino acid that is chemically similar
Frameshift mutation
Insertion/deletion of nucleotides
If not multiple of three it will disrupt frame
Amino acid sequence of protein subsequent to mutation doesn’t resemble normal strand
Polymorphism
Common variant in DNA sequence - benign
Variant
Alteration that can be benign, pathogenic or unknown
Mutation
Change in DNA sequence - rare and causes disease
