Gene Mutation and Transposable Elements Flashcards
Somatic mutations
affect only the individual in which they arise; are not transmitted to progeny; in diploid heterozygous individuals, only dominant somatic mutations will be expressed
Germline mutations
alter gametes, affecting the next generation; transmitted to progeny
Which has more effect, early somatic mutation or late somatic mutation?
Early somatic mutation because it affects a larger population
Base substitutions
replaces one base w/ another; two types: transitions and transversions
Transitions
converts purine to purine and pyrimidine to pyrimidine; Ex: A to G or T to C
Transversions
converts a purine to pyrimidine or to a pyrimidine to purine; Ex: A to T or C to G
Silent or synonymous mutations
encodes for same amino acid as in wild type gene, so that no change occurs in protein produced
Nonsense mutations
encodes for a stop codon, resulting in premature termination of translation and often nonfunctional protein
What are the 3 stop codons?
UGA, UAA, UAG
Conservative (neutral) missense mutation
changes codon in ORF, but resulting amino acid is similar to one substituted producing no detectable change in protein function; Ex: AGA to AAA substitutes Arg for Lys which have the same properties, so protein function is not altered
Non-conservative missense mutation
changes codon in ORF resulting in different amino acid to one substituted, producing change in protein fucntion; Ex; AGA to ATA substitutes Arg for Ile: amino acid’s have diff. properties, so protein function is altered
Base insertions/deletions (InDels)
of base number not divisible by 3, can cause frameshift mutation
frameshift mutation
can change reading frame of mRNA downstream of mutation; causes a shift due to an InDel
Spontaneous
most mutations are spontaneous; most of them are corrected by cellular repair system
Depurination
disconnection of G or A from DNA sugar phosphate backbone; usually repaired
Deamination
removes an amino group from a base; Ex: NH2 removed from C -> becomes uracil; if not repaired, CG will convert to TA (transition)
Induced
exposure to physical and chemical mutagens
X-ray and other ionizing radiation
breakage of covalent bonds
UV radiation
crosslinking between adjacent pyrimidine bases
Base modifying agents
a chemical mutagen like ethyl methane sulfonate which causes a linkage from guanine to 6-ethylquanine and thymine
Null mutation
loss of function mutation; eliminates crucial function of a gene; recessive mutations
Leaky mutation
reduced function; inactivation is incomplete
Gain of function
conifers a new function on the gene; dominant mutations
Transposable elements
randomly insert themselves in chromosomes, causing genetic changes
