Molecular Evolution Flashcards
Define synonymous substitution. On what codon position does it usually occur?
Substitution that does not change amino acid or protein (non-point mutation) evolution occurs about 5 times faster compared to nonsynymous. Third position (i.e., ACU → ACC, threonine ).
Define nonsynonymous substitution. On what codon position does it usually occur? Always occur?
A change in a gene from one nucleotide to another that changes the amino acid specified by the corresponding codon. Usually in 1st (GUU → GCU, or valine → alanine) always in 2nd position (CAG → AAG, or glutamine → lysine).
Define mutation
Change in allele frequencies by continually introducing new alleles. Usually deleterious.
Define genetic drift
Causes allele frequencies to change randomly. In some cases, drift may even cause alleles that decrease fitness to increase in frequency
Define population
A group of individuals from the same species thatt live in the same area and regularly interbreed.
Define genetic variation
The number and relative frequency of alleles that are present in a particular population
Due to genetic drift, (small / large) populations have higher levels of genetic variation
Large
Define mutation rate
The probability that a particular copy of a particular allele will be inaccurately replicated, resulting in an allele with a different nucleotide sequence.
Define nucleotide substitution rate
The rate at which one nucleotide gets substituted for another at a particular DNA position over evolutionary time. It is affected by several factors other than the mutation rate, including the strength and direction of natural selection and the population size.
Due to genetic drift, synonymous substitutions are likely to occur in (high/low) frequencies in a population and to
(increase/ decrease).
High, Increase. Because they are unlikely to have any effect on phenotyope, they may reach high frequency, and even become fixed (frequency raised to 100%).
Due to natural selection, nonsynonymous substitutions are likely to (increase/decrease) in a population
Decrease. Because they are usually deleterious, so natural selection will reduce their frequecies to zero.
In large populations, there is (less/more) genetic drift
Less. Frequencies change less rapidly
In large populations, there is (less/more) genetic variation
More
Define pseudogenes
DNA sequences that resemble functional genes, but have lost their protein-coding ability or are no longer expressed. These often form after a gene has been duplicated, when one or more of the redundant copies subsequently lose their function.
