genetic variation in disease Flashcards
Allelle
alternative forms of gene/locus/variant
Homozygous
two copies of same allele at same locus (genotype AA or BB)
Heterozygous
different alleles at same locus (genotype AB or BA)
Autosomes
anything but sex chromosomes
how many base parts is a codon made of
3
what sequence of bases encodes for methionine and starts the translation of all proteins
AUG
how many codons encode for the 20 amino acids ( redundant code)
61
how many codons stop translation of proteins
3
UGA
UAA
UAG
3 types of DNA variation
single base substitutions ( SNPs - single nucleotide polymorphisms)
deletions
insertions
what is a synonymous/silent variation
No change to the amino acid sequence
No change in function
Doesn’t not cause disease
what is a non-synonymous mutation
Changes amino acid sequence of protein
Can changes structure of the protein
Can change function of the protein
Can cause disease and normal variation
silent mutation
mutation does not alter the polypeptide product of the gene
often single pair substitution a the third position of a codon
triplet codes for same aa
no alteration in properties of the resulting proteins
could be outside of the coding region - in an intronic region
where is the most common place for a silent mutation
third position of a codon
nonsense mutation
stop codon formation terminating translation
express truncated protein
nonsense mediated decay is a form of what
RNA surveillance that is believed to have evolved to protect the body from the possible consequences of truncated proteins interfering with normal function.
mRNA is degraded by what
nonsense-mediated decay so NO protein is made.
missense mutation
codes for different aa
can be chemically dissimilar and similar
2 types of missense mutation
non-conservative substitution
conservative substituions
non-conservative substitution
Gross reduction, or even a complete loss, of biological activity.
Qualitative changes in the function of a protein may also occur
Ie the protein retains its normal biological activity but maybe less stable for example
conservative substitution
Some single base-pair substitutions result in the replacement of a different amino acid that is chemically similar,
No or very little difference in functional effect.
frameshift mutation
inseriton or deletion of nucleotides - if not a multiple of 3 ( non frameshift) will always disrupt the reading frame - usually premature stop leading to truncated protein
variant
Variant can be used to describe an alteration that may be benign, pathogenic, or of unknown significance. The term variant is increasingly being used in place of the term mutation.
mutation
Mutation – rare variant in DNA sequence – disease causing
polymorphism
Polymorphism - common variant in DNA seqeunce – benign (does not cause disease) present in >1% of the population
cDNA sequence
Complementary DNA (No introns, only coding sequence, derived from mRNA sequence, same as coding strand of DNA without introns)
