Chapter 15 Flashcards
evolution
change in genetic composition of populations over time
evolutionary theory
understanding and applying the processes of evolutionary change to biological problems
descent with modification
share a common ancestor and have diverged from one another gradually over time
natural selection
increased survival and reproduction of some individuals compared with others based on more favourable traits
population
group of individuals of a singe species that live and interbreed in a particular geographic area at the same time
what is the origin of genetic variation?
mutation
alleles
different forms of a gene
adaptation
favoured trait that evolves through natural selection
gene flow
migration of individuals and movements of gametes between populations can change allele frequencies
population bottleneck
populations that are normally large but pass through environmental events that only a small number of individuals survive
what happens if a population goes through a bottleneck?
it loses variation
founder effect
change in genetic variation w hen a few pioneering individuals colonise a new region
why do mating patterns alter genotype frequencies?
individuals in a population do not choose mates at random
sexual selection
occurs when individuals of one sex mate preferentially with particular individuals of the opposite sex
what is the opposite of sexual selection?
random mating
what is the formula for allele frequency?
p = (number of copies of the allele in the population)/(total number of copies of all alleles in the population)
what are the Hardy-Weinberg equations?
p + q = 1
p + 2pq + q = 1
Hardy-Weinberg equilibrium
describes a model where allele frequencies do not change across generations and genotype frequencies can be predicted from allele frequencies
what are the conditions of HW equilibrium?
no mutation, no selection among genotypes, no gene flow, infinite population size, random mating
qualitative traits
discrete qualities
quantitative traits
likely to show continuous quantitative variation
stabilising selection
preserves the average characteristics of a population by favouring average individuals
directional selection
changes the characteristics of a population by favouring individuals that vary in one direction from the mean of the population
disruptive selection
changes the characteristics of a population by favouring individuals that vary in both directions from the mean of the population
purifying selection
selection against any deleterious mutations to the usual gene sequence
positive selection
favouring one phenotype over another
synonymous substitution
substitution that does not change the encoded amino acid
silent substitution
synonymous with synonymous substitution
nonsynonymous substitution
does change the amino acid sequence encoded by a gene
missense substitution
synonymous with nonsynonymous substitution
pseudogenes
copies of genes that are no longer functional
N
population size
μ
neutral mutation rate
average number of new mutations
μ * 2N
m
rate of fixation of neutral mutations
formula for rate of fixation of neutral mutations
m = 2Nμ(1/N)
why can a heterozygous condition never become fixed in a population?
offspring of two heterozygotes will always include both classes of homozygotes
disadvantages of sexual reproduction
recombination breaks up adaptive combinations of genes, reduces the rate of females passing genes on to offspring, dividing offspring into separate genders reduces the overall reproductive rate
what is the effective reproductive rate of the asexual lineage?
twice that of the sexual lineage
Muller’s ratchet
accumulation of deleterious mutations in lineages that lack genetic recombination
advantages of sexual reproduction
facilitates repair of damaged DNA, permits the elimination of deleterious mutations
how does sexual reproduction eliminate deleterious mutations?
through recombination followed by selection
lateral gene transfer
horizontal movement of individual genes, organelles, or fragments of genomes from one lineage to another
gene duplication
allows genomes to acquire new functions
gene family
group of homologous genes with related functions
how does a gene family arise?
several successive rounds of duplication and sequence evolution
in vitro evolution
new molecules are produced in the lab to perform new and useful functions
