Chapter 23 Flashcards
microevolution is defined at
a change in the allele frequency of a population from one generation to another
_______________ is evolution at its most fundamental levels. Change within a population.
microevolution
evolution operates on __________________
genetic variability
the combination of darwinian evolution and mendelian genetics is referred to as the modern synthesis
genetic variability
two processes produce the genetic variation on which evolution acts
- mutations
- sexual reproduction
changes in the nucleotide sequences of DNA
Mutations
Mutation can
be harmful or have no effect
mutation may occasionally confer an advantage and be selected for
mutations are responsible for producing new allies, new genes, and ultimately all of the diversity of life.
____________________ rearranges existing alleles into new combinations by way of three mechanisms
sexual reproduction
- crossing over
- independent assortment of chromosomes
- random fertilization
___________________ is a larger contributor to genetic variability than are mutations in sexual organisms
reproduction
allele are ____________________________ within a population
alternative forms of genes
_______________ consists of all of the alleles for all of the genes within all of the individuals in the population
populations gene pool
the portion of a population that is dominate is represented by
P
the portion of a population that is recessive is represented by
q
equation of p and q
p + q=1
knowing allele frequency allows us to determine
genotype frequency
proportion of homozygous dominant
p^2
proportion of heterozygous
2pq
the proportion of homozygous recessive
q^2
the hardy-weignberg equation
p^2+2pq+q^2
if the allele and genotype frequencies remain the same from one generation to the next the population is in Hardy-Weinberg equilibrium
it is not evolving
if allele and genotype frequencies do change from generation to another, the population is undergoing
microevolution
there mechanisms cause allele frequencies and therefore genotype frequencies to change with in the population
genetic drift
gene flow
natural selection
____________ is the change in the allele frequencies of small populations due to ______________
genetic drift
_____________ can increase or decrease the proportion of helpful or harmful alleles. tends to reduce genetic variability within a population over time
genetic drift
two examples of genetic drift
- bottleneck effect
- founder effect
_______________ occurs when a few individuals become isolated from a larger population thereby colonizing a new smaller population
the founder effect
_____________________ occurs when a population’s size is significantly reduced often by natural disaster
bottleneck effect
in both cases, allele frequencies in the new smaller population may by chance ____________________________________________
be different from allele frequencies in the original larger population
________________ is the transfer of alleles between populations
gene flow
allele are transferred due to the movement of _______________
individuals and their gametes
gene flow can increase or decrease the proportion of
helpful or harmful alleles
gene flow tends to reduce genetic variability
between populations over time
-the gene pools of the populations become more similar
____________ is unequal reproduction
natural selection
natural selection is only ___________________ that consistently promotes __________________________
microevolutionary mechanism
adaptive evolution
populations become better _____________ to their environments over time as advantageous alleles are passed among generations to greater proportions
adapted
___________ increase the frequency whole harmful allele decrease during ______
helpful allele
natural selection
for population to be in Hardy Weinberg equilibrium (allele and genotype frequencies remain constant from one generation to the next; the population is not evolving) the population must be
- the population must be very large
- genetic drift as a result would have no effect
more qualifications for Hardy Weinberg equilibrium
- there must be no movement of individuals or their gametes into immigration or out of emigration a population
- natural selection must not occur
- there must be no mutations
- mating must have no mutations: individuals within a population cannot preferentially choose mates this would affect the random fertilization
how common is Hardy Weinberg equilibrium
not very alleal frequencies are changing, microevolution is constantly occurring, populations are constantly evolving
two type of balancing selection
- frequency dependent selection
- heterozygote selection
__ is being defined as an individuals contribution on the next generations gene pool
fitness
the number of offspring an individual produces relative to the number of offspring produce by all other individuals in the population
fitness
natural selection results in competitively superior individuals surviving and reproducing
these individuals have the greatest fitness
________________________ changes the frequencies of allele and genotypes in a population based on which phenotypes are favored
natural selection
one extreme of a phenotype is selected for
ex- dark rat
directional selection
both extremes of a phenotype range are selected for
ex- dark and white rat
disruptive selection
intermediate phenotype is selected for
ex- brown rat
stabilizing selection
_____________________ occurs when natural selection maintains two or more phenotypes within a population and helps to preserve the populations genetic diversity
balancing selection
__________________________ the fitness of a phenotype depends on how common it is in the population
frequency dependent selection
frequency dependent selection:
the fitness of a phenotype ________________ if the phenotype becomes too common. Selections favor less common
decline
_______________ occurs when individuals heterozygous for a particular gene have higher fitness than individuals homozygous dominant or homozygous recessive for that gene
heterozygous advantage
heterozygous advantage maintains
both alleles for the gene within a given population
In certain regions of africa _______________________ suffer from sickle cell disease
4% of the population suffers from sickle sell disease
q^2=0.04
sick cell is a __________________
a homozygous recessive disorder
why is the frequency of sickle cell high wouldn’t the individual die before they can reproduce
sick cell has an advantage. resistance to malaria which is supper prevalent in some regions of malaria
____________________ individuals are protected against malaria but have sickle cell
____________ individuals are not protected against malaria but do not have malaria
____________________ individuals are protected against malaria and do not have sick cell
homozygous recessive
homozygous dominant
heterozygous
example of heterozygous example
q^2=0.04
q=0.2
p=0.8
2pq=0.32
the sick cell allel is helpful to 32% to population but only harmful to 4% of the population so it permits
sexual selection is a form of
natural selection
______________ if the limited resource for which individuals compete for is
mates
the “environment” selects for advantageous traits is
opposite sex
sexual selection frequently results in
sexual dimorphism
differences in size color ornamentation and behavior of the two sexes
sexual dimorphism
natural selection can only select for __________________ which may not be the most advantageous traits
existing variations
natural selection is contracted by
descent with modification
adaptions are often ___________
compromises or trade offs
natural selection has to interact with other mechanisms of evolution as well as with a potentially
changing environment
