Chapter 15 | Molecular Evolution Flashcards
define the neutral theory of molecular evolution
the majority of mutations are neutral, and may fix in populations through genetic drift
rate of fixation of neutral mutations by genetic drift is
independent of population size
rate of fixation is equal to
the neutral mutation rate
what is meant by most of mutations are neutral?
they serve no benefit or non-benefit to the survival of the organism
to the random fluctuation of allele frequencies in a population from one generation to the next due to chance events
genetic drift
if most mutations are neutral, and the mutation rate is constant
macromolecules evolving in different populations should diverge from one another at a constant rate
why do most nucleotide changes in coding regions have no effect at the protein level?
most amino acids are specified by more than one codon, often ending up being a silent change
a substitution that does not change the amino acid
synonymous or silent substitution
a substitution that does cause a change in the amino acid
nonsynonymous substitution (from a missense mutation)
nonsynonymous substitutions are often
deleterious
protein shape and function is not always altered in nonsynonymous substitutions, so it may be
selectively neutral or possible beneficial
which substitution occurs more frequently than the other?
synonymous substitutions
are the rates of nonsynonymous substitutions equal in all genes?
no; they vary, and are higher in some genes than others
what does a ratio of 1 between synonymous and nonsynonymous substitutions suggest?
the amino acid replacement is neutral
copies of genes that are no longer functional
pseudogenes
evolutionary rates are
higher in pseudogenes
synonymous / nonsynonymous < 1
the amino acid is under position selection for change
synonymous / nonsynonymous > 1
the amino acid is under purifying selection
what allows scientists to determine history and timing of synonymous and nonsynonymous substitutions?
comparing gene sequences among species
defense mechanism against bacteria
lysozyme
what is evolutionary convergence?
unrelated organisms develop similar traits or characteristics independently as they adapt to similar environmental challenges
the probability of fixation for all three codon positions
are influenced by selection
regions of chromosomes can be duplicated through
chromosomal mutations
what are some fates of duplicate genes?
(1) both copies retain original function (more product can be made)
(2) one copy becomes nonfunctional and turns into a pseudogene
(3) both copies retain original function but expression diverges in different tissues or at different times
(4) one copy accumulates substitutions that allow it to perform new function
