The evolution of populations
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| ___ makes evolution possible. | Genetic variation
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| The Hardy-Weinberg equation can be used to test whether a population is ___. | evolving
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| Natural selection, genetic drift, mutations, and gene flow can alter ___ in populations. | allele frequencies
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| ___ is the only mechanism that consistently causes adaptive evolution. | Natural selection
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| What does this mean: populations evolve, not the individual members of populations. | allele frequencies in a population are changing over time, individuals aren't evolving
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| microevolution | evolutionary change below the species level; change in the allele frequencies in a population over generations
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| What’s the story about the medium ground finch population on the island of Daphne Major in the Galápagos Islands? | - there was a drought that caused small, soft seeds to become more rare
- many finches died b/c they could not eat the plentiful hard seeds
- those in the population that had bigger/stronger beaks survived and passed on their genes
- %stronger beaks ^
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| What were Darwin’s thoughts about variation in inherited traits and what did that mean for the process of natural selection? | - variation in heritable traits is a prerequisite for evolution
- natural selection is the primary mechanism of evolution
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| What exactly is natural selection and what does natural selection act on? | - a process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals BECAUSE OF those traits
- phenotypic traits
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| phenotypic variation | the variability in phenotypes (observable traits) that exists in a population
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| genetic variation | differences in the composition of genes among individuals in a population
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| Does genetic variation necessarily manifest itself as outwardly observable phenotypic variation? | - no
- ex: carriers
- ex: you cannot ID a person's blood group from their appearance
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| Does phenotypic variation have to result from genetic variation? | - no
- phenotype is the product of an inherited genotype AND many environmental influences
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| What's the deal with moth caterpillars? | - they are genetically similar
- the differences in their appearance come from the differences in their diet
- ones that eat oak flowers look like oak flowers, ones that eat oak leaves look like oak twigs
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| How does mutation create new alleles? | - a change of as little as one base in a gene, called a point mutation, can have a significant impact on phenotype
- ex: sickle cell disease; a point mutation can change what codon is made, which will then change what amino acid is made
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| How might gene number or position be altered? | deletions, duplications, inversions, and translocations
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| Mutation rates tend to be low, so how does rapid reproduction affect the spread of new alleles in a population? | - Organisms that reproduce more often (have short generation spans) mutate more often too
- like bacteria mutating resistance to antibiotics
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| Mutation rates tend to be low, so how does sexual reproduction affect the spread of new alleles in a population? | - most of the genetic differences among individuals result from crossing over, the independent assortment of chromosomes, and fertilization
- so, few mutations can go a long way thanks to sexual recombination
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| population | a group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
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| gene pool | the aggregate (whole) of all copies of every type of allele at all loci in every individual in a population
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| What’s the deal if only one allele exists for a particular locus in a population? | - then that allele is said to be FIXED in the gene pool, and all individuals are homozygous for that allele
- no variation
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| What’s the deal if two or more alleles exist for a particular locus in a population? | - individuals may be either homozygous or heterozygous
- variation possible
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| Each allele has a ___ in a population. | frequency/proportion
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| Suppose that in a population there are 320 plants with red flowers, 160 with pink, and 20 with white. How many copies of the flower color gene are in the population? | because these are diploid individuals, there are a total of 1,000 copies of the gene for flower color in the population of 500 individuals
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| Suppose that in a population there are 320 plants with red flowers, 160 with pink, and 20 with white. What is the frequency of the CR allele (p)? What is the frequency of the CW allele (q)? | - the C^R allele accounts for 800 (320x2 + 160) copies of the flower color gene out of 1000; 80%
- because there are only two alleles for this gene, the frequency of the C^W allele must be 20% (p+q=1)
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| What does it mean for a population to be at Hardy-Weinberg equilibrium? | the frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work
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| Suppose that in a population there are 320 plants with red flowers, 160 with pink, and 20 with white. What is the probability that two C^R alleles will come together? | - the C^R allele accounts for 800 (320x2 + 160) copies of the flower color gene out of 1000; 80%
- p x p = p^2 = .8 x .8 = .64 = 64%
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| Suppose that in a population there are 320 plants with red flowers, 160 with pink, and 20 with white. What is the probability that two C^W alleles will come together? | - the C^R allele accounts for 800 (320x2 + 160) copies of the flower color gene out of 1000; 80%
- because there are only two alleles for this gene, the frequency of the C^W allele must be 20% (p+q=1)
- q x q = q^2 = .2 x .2 = .04 = 4%
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| Suppose that in a population there are 320 plants with red flowers, 160 with pink, and 20 with white. What is the probability that a C^R allele and a C^W allele will come together? | - the C^R allele accounts for 800 (320x2 + 160) copies of the flower color gene out of 1000; 80%
- because there are only two alleles for this gene, the frequency of the C^W allele must be 20% (p+q=1)
- 2 x p x q = 2pq = 2 x .8 x .2 = .32 = 32%
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| One of the conditions for Hardy-Weinberg Equilibrium is no mutations. Why? | because the gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated
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| One of the conditions for Hardy-Weinberg Equilibrium is random mating. Why? | if individuals mate preferentially within a subset of the population, random mixing of gametes does not occur, and genotype frequencies change
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| One of the conditions for Hardy-Weinberg Equilibrium is no natural selection. Why? | differences in the survival and reproductive success of individuals carrying different genotypes can alter allele frequencies
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| One of the conditions for Hardy-Weinberg Equilibrium is extremely large population size. Why? | the smaller the population, the more likely it is that allele frequencies will fluctuate by chance from one generation to the next (genetic drift)
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| One of the conditions for Hardy-Weinberg Equilibrium is no gene flow. Why? | by moving alleles into or out of populations, gene flow can alter allele frequencies
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| What does the departure of Hardy-Weinberg Equilibrium conditions lead to? | evolutionary change
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| How can a population be evolving in some ways and be at equilibrium in other ways? | - an individual has many different genes
- so, allele frequencies could be staying the same for some genes but changing for others
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| Phenylketonuria (PKU), a recessive condition (i.e., the people with PKU are homozygous recessive), occurs in about 1/10k babies born in the US. What can we figure out simply by knowing the frequency of individuals in the population who have PKU? | - freq. of those born with PKU = q^2 (since homo. recessive), so q^2 = .0001
- the freq. of the rec. allele then is sqrt(.0001) = .01 = q
- therefore, the freq. of the dominant allele p must be .99
- freq. of carriers would be 2 x .99 x .01 = .0198
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| How can natural selection alter allele frequencies in a population? | - by consistently favoring some alleles over others
- causes adaptive evolution
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| What is genetic drift? When are its effects the most pronounced? | - a process in which chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
- in small populations
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| founder effect | genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population
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| bottleneck effect | - genetic drift that occurs when the size of a population is reduced, as by a natural disaster or human actions
- typically, the surviving population is no longer genetically representative of the original population
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| What are the similarities and differences between the founder and bottleneck effects? | - sim: reduce genetic diversity; random
- diff: the cause (separation vs. decimation)
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