Exam 1 PPTs - 7 Flashcards
Genetic Drift vs. Natural Selection:
- In an ideal population of infinite size, …. favoring one allele over others will inexorably carry the favored allele to …
- If the same beneficial allele occurs in a finite population, however, … will cause the allele’s frequency to fluctuate at … around the trajectory it would have taken in a population of … size
natural selection; fixation; sampling error; random; infinite
Genetic Drift vs. Natural Selection:
- Likewise, in an infinitely large population, … favoring heterozygotes will maintain multiple alleles at … indefinitely
- in a finite population, … may cause one allele to become … and the other to be …
selection; equilibrium frequencies;
genetic drift;
fixed;
lost
Genetic Drift vs. Natural Selection:
whether drift or selection plays the predominant role in determining the evolutionary outcome will depend on both the …. and the …
size of the population;
strength of selection
Genetic Drift vs. Natural Selection:
- Stephen S. Rich and colleagues (1979) studied the interplay between natural selection and genetic drift in lab populations of the …
- Rich and colleagues took advantage of genetic variation for color at the b locus
- Beetles with genotype b+/b+ are red, beetles with genotype b+/b are brown and beetles with genotype b/b are black.
- Rich and colleagues set up 24 populations of flour beetles in which the initial frequencies of allele b+ and allele b were both …
red flour beetle;
0.5
Genetic Drift vs. Natural Selection:
- Rich and colleagues started 12 populations with … males and … females and 12 with … males and … females
50;
50;
5;
5
Genetic Drift vs. Natural Selection:
- Rich and colleagues maintained the populations at these sizes for … generations, each generation choosing adults at random to serve as … for the next gen
20;
breeders
Genetic Drift vs. Natural Selection:
- Every generation Rich and colleagues examined … … chosen individuals from each population to assess the … of the two alleles
240; randomly;
frequencies
Genetic Drift vs. Natural Selection:
- Rich’s results for the bigger population showed a pattern consistent with …
- The researchers estimated the relative fitnesses of genotypes b+/b+, b+/b, and b/b to be 1, 0.95, and 0.9
natural selection
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- There are three kinds of mutations: …, … and …
deleterious;
neutral;
beneficial
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- mutations that are deleterious tend to be … by natural selection
- mutations that are neutral (or nearly so) … as a result of genetic drift
- mutations that are beneficial are often … while still at low frequency, but otherwise tend to … as a result of natural selection
eliminated;
rise and fall in frequency;
lost to drift;
rise to fixation
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- the study of molecular evolution began in the mid - 1960s, when biochemists succeeded in determining the … of hb, cytochrome c, and other abundant and well-studied proteins found in humans and other vertebrates
- these sequences provided the first opportunity for evolutionary biologists to compare the … and … of … among species
amino acid sequences;
amount; rate; molecular change
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- Kimura took the number of sequence differences in the well-studied proteins of humans vs horses and converted them to … using divergence dates estimated from the …
rates of sequence change over time;
fossil record
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- Kimura took the number of sequence differences in the well studied proteins of humans versus horses and converted them to rates of sequence change over time using divergence dates estimated from the fossil record
- For example, if the species are humans and mice, their common ancestor prob lived about 80 mya. If we look at the sequence of a 100 aa protein in the two species and it differs at 16 sites, then the rate of evolution is estimated at: …. per aa site per Ma
16/100/(80*2) is about 0.001
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- Rates of molecular evolution are arguably too … for a process controlled by …
constant;
natural selection
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- Kimura’s neutral theory holds that effectively … mutations that rise to fixation by … vastly outnumber … mutations that rise to fixation by …
neutral;
drift;
beneficial;
natural selection
The Neutral Theory of Molecular Evolution:
Kimura (1968, 1983)
- …, not … is thus the mechanism responsible for most molecular evolution
- most mutations are …
genetic drift;
natural selection;
neutral
… sites change faster than … sites in most coding loci
silent;
replacement
controversy about the neutral theory
- discussion has focused on the claims that that the number of beneficial mutations fixed by positive natural selection is … compared to the number of mutations that change in frequency under the influence of …
inconsequential;
drift
Genetic drift vs natural selection at the molecular level:
- we can compare two sequences and calculate the rate of nonsynonymous substitutions per site (dN) an the rate of synonymous substitutions per site (dS):
dN/dS < 1 when replacements are ….
dN/dS = 1 when replacements are …
dN/dS > 1 when replacements are …
deleterious;
neutral;
advantageous
Genetic drift vs natural selection at the molecular level:
- Austin Hughes and Masatoshi Nei (1988) tested the neutral theory by estimating the ratio of … to … in genes vital to … function
replacement;
silent substitutions;
immune
Genetic drift vs natural selection at the molecular level:
- when mammalian cells are infected by a bacteria or a virus, they respond by displaying pieces of bacterial/viral … on their surfaces. Immune system cells then … the infected cell, which prevents the bacterium or virus inside the cell from …
protein;
kill;
replication
Genetic drift vs natural selection at the molecular level:
- ….: cluster of genes encoding the membrane proteins that display pathogen proteins
- Hughes and Nei (1988) studied sequence changes in MHC loci in humans and mice, they found significantly more … site than … site changes
major histocompatibility complex (MHC);
replacement;
silent
Genetic drift vs natural selection at the molecular level:
- Hughes and Nei studied sequence changes in MHC loci in humans and mice, they found significantly more replacement site than silent site changes
- this pattern could only result if the replacement changes were …
- … causes replacement changes to spread through the population much more quickly than … alleles can spread by …
selectively advantageous;
positive selection;
neutral; chance
Genetic drift vs natural selection at the molecular level:
- Research by Gavin Huttley and colleagues (2000) on BRCA1, a gene associated with breast cancer, provides another example. BRCA1 encodes a protein that participates in the … and in the regulation of … during … development
repair of damaged DNA;
programmed cell death;
neural
The nearly neutral theory of molecular evolution:
the neutral theory of molecular evolution explains:
- the … evolution of nucleotide sequences
- why … substitutions outnumber … substitutions in most genes
- and the neutral theory serves as a … that allows researchers to identify examples of … on nucleotide sequences
clock-like;
silent; replacement;
positive selection
The nearly neutral theory of molecular evolution:
- … developed a modified version of the neutral theory
- for a nearly neutral mutation, the relative power of drift and selection depends on …
population size
The nearly neutral theory of molecular evolution:
- nearly neutral mutations behave as … in small populations and their fate is determined by …
- they behave as … mutations in large populations and their fate is determined by …
neutral mutations;
random drift;
non-neutral mutations;
selection
