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
In prokaryotes, what are the types of transposable elements?
insertional sequences (IS) and transponsons
Insertional sequences
have IRs at the ends and encode transposase required for transposition
Transposons
similar to IS but have additional genes
In eukaryotes, what are the types of TEs?
structure is similar to prokaryotic TEs; have genes for transposition (Ac element) and integration (Ds element)
Ds element
results in colorless corn compared to the wild type (pigmented)
Ac element
results in spotted kernels
What are the possible effects of TEs in eukaryotes?
Disruption of genes to produce a null mutation
Activation or repression of adjacent genes by disrupting a cellular promoter or by action of transposon promoters
Chromosome mutations such as duplications, deletions, inversions, translocations, or breakage
