Chapter 23 Evolution of Populations Flashcards
Do organisms evolve during their lifetimes?
No, only natural selection
What does natural selection act on?
Genetic variation, different phenotypes.
Can populations evolve?
Yes
*there must be a change in ___________ for evolution to take place
Allele frequencies
What is a change in allele frequency‘s in a population over generations?
Microevolution
In microevolution what are the three mechanisms that cause allele frequency change?
-natural selection -genetic drift -Gene flow
Only ___________ causes adaptive evolution
Natural selection
What is the mechanism that improves the match between the organism and its environment?
Natural selection
What is the mechanism that can cause a change in the gene pool of a small population strictly by chance?
Genetic drift
The transfer of genetic variation from one population to another coming or leaving the population
Gene flow
What is a prerequisite for evolution?
Genetic variation in heritable traits
Genetic variation among individuals is caused by ____________.
Differences in genes or other DNA segments
What contributes to phenotypic differences?
Single gene or Two or more genes (quantitative characters)
Average heterozygosity measures the average percent of loci that are heterogeneous in a population
Gene variability *more valuable measurement compared to nucleotide variability
Measured by comparing the DNA sequence of pairs of individuals
Nucleotide variability
How do you new genes and alleles arise?
-mutation -gene duplication -exon shuffling
What are other sources of genetic variation?
-horizontal gene transfer -sexual reproduction
-a change in nucleotide sequence of DNA
Mutation
Only mutations in cells that produce ________ can be passed offspring
Gametes (egg or sperm)
What is a change in one base in a gene?
Point mutation
Why can mutations to genes be neutral?
No change to the amino acid being made, it’s silent no change in the phenotype Or mutations that occur in the introns
differences in DNA sequence that do not confer a selective advantage or disadvantage Ex: mutations in non-coding regions of DNA
Neutral variation
Duplicated genes can take on new __________ by further mutation Ex. Globins (hemoglobin, myoglobin)
Functions
Are mutation rates higher or lower in animals and plants? With a Mutation rate of…
Low 1 in every 100,000 genes per generation
Mutations rates are often ________ in prokaryotes and ________ in viruses
Lower, higher
Why do most mutations accumulate quickly in prokaryotes in viruses?
Shorter lifespan (20-30 min)
sexual reproduction can shuffle existing alleles into new combinations by what three ways?
-crossing over -independent assortment of chromosomes -fertilization
In organisms that reproduce sexually, _________ of alleles is more important than mutations in producing the genetic differences that make adaptation possible
Recombination
What equation is used to test whether a population is evolving?
Hardy-Weinberg Equation P^2 + 2pq + q^2 = 1
p= q= p^2= 2pq= q^2=
p= frequency of dominant allele q= frequency of recessive allele p^2= Frequency of AA genotype 2pq= frequency of Aa genotype q^2= Frequency of aa genotype
A localized group of individuals capable of interbreeding and producing fertile offspring
Population
Consists of all the alleles for all loci in a population
Gene pool
The Hardy-Weinberg principle describes a population that is…..
Not evolving
If a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is __________
Evolving
Principle that states frequencies of alleles and genotypes in a population remain constant from generation to generation
The Hardy-Weinberg principle
Describes the constant frequency of alleles in a gene pool
Hardy-Weinberg equilibrium
Describes a hypothetical population that is not evolving
The Hardy-Weinberg theorem
*** in the Hardy-Weinberg theorem what are the five conditions for non-evolving populations (rarely met in nature)
- No mutations 2. Random mating 3. No natural selection 4. Extremely large population size 5. No gene flow
Natural populations can evolve at some loci, while being in Hardy-Weinberg equilibrium at other loci. True or false?
True
Phenylketonuria (PKU) that occurs 1 in every 10,000 births (2% of the U.S. population) is an example of ….
Hardy-Weinberg equilibrium
What are the three major factors that alter allele frequencies and bring about most evolutionary change?
-natural selection -genetic drift -Gene flow
How does natural selection alter allele frequency?
Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions
How does genetic drift alter allele frequency?
-changes Clearlake frequency due to random chance -describes how allele frequency‘s fluctuate unpredictably from one generation to the next
Will a smaller or larger sample have a greater chance of deviation from a predicted result?
Smaller
How does genetic drift tend to reduce genetic variation?
-
What effect can be seen when a few individuals become isolated from a larger population? Can allele frequencies in this smaller population be different from those in the larger parent population?
The founder effect Yes, does not match the parent population
What effect is seen when there is a sudden reduction in population size due to a change in the environment?
The bottleneck effect
With the bottleneck effect, is the resulting gene pool reflective of the original populations gene pool?
No. There is less genetic variation than the original population. If the population remain small, it may be further affected by genetic drift
-population reduced dramatically and then rebuilds -randomly eliminated members without regard to genotype -surviving members may have allele frequencies different from original population -Allele frequencies can drift substantially when the population is small -New population likely to have less genetic variation
Bottleneck effect
Understanding the _________ effect can increase understanding of how human activity affects other species
Bottleneck
Genetic drift is significant in ________ populations Genetic drift causes allele frequencies to change at __________
Small Random
Genetic drift can lead to a loss of genetic _________ within populations Genetic drift can cause harmful alleles to become __________
variation Fixed
Consists of the movement of alleles among populations Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen)
Gene flow
* Gene flow tends to _______ variation among populations over time * tends to ________ genetic diversity within a population
Reduce Enhance
Can gene flow decrease the fitness of a population?
It increases the fitness of the population
Gene flow can __________ the fitness of a population
Increase Ex: resistance to insecticide can be passed to other populations and increase their fitness
____________ is an important agent of evolutionary change in human populations
Gene flow
______________ is the only mechanism that consistently causes adaptive evolution
Natural selection
In Evolution by natural selection…. New genetic variations arise by ________ Beneficial alleles are “_______” and favored by natural selection
Chance Sorted
Leaving genes for the next generation The contribution of an individual makes to the gene pool for the next generation, relative to the contributions of other individuals
Relative fitness
Selection favors certain genotypes by acting on what of individuals?
Phenotypes
What are the three modes of selection?
-directional selection -destructive selection -stabilizing selection
A mode of selection that favors individuals at one end of the phenotypic range (an extreme is picked)
Directional selection
Selection that favors individuals at both extremes of the phenotypic range
Disruptive selection
Mode of selection that favors intermediate variance and acts against extreme phenotypes
Stabilizing selection
Does genetic drift and gene flow consistently lead to adaptive evolution?
No. They can increase or decrease the match between the organism and it’s environment
natural selection for mating success
Sexual selection This can cause sexual dimorphism
the differences in secondary sexual characteristics between males and females of the same species
Sexual dimorphism
Selection within the same sex, individuals of one sex compete directly for mates of the opposite sex.
Intrasexual selection
Also called mate choice, one sex is choosy in selecting their mates from the other sex
Intersexual selection
Balancing selection includes…
-heterozygote advantage (ex: malaria protection in heterozygous for sickle cell) -frequency-dependent selection
Occurs when natural selection maintain stable frequencies of two or more phenotypic forms in a population
Balancing selection
-occurs when heterozygotes have a higher fitness then do both homozygotes -natural selection will tend to maintain two or more alleles at that locus -can result from stabilizing or directional selection
Heterozygote advantage
The fitness of a phenotype declines if it becomes too common in the population Selection can favor which ever phenotype is less common in a population Selects for approximately equal numbers Ex: right-mouth and left-mouth fish
Frequency-dependent selection
Genetic variation that does not confer a selective advantage or disadvantage
Neutral variation
