Chapter 23 Flashcards
micro evolution
the change in allele frequencies in a population over generations
what are three things that cause allele frequency change?
- natural selection
- genetic drift
- gene flow
what causes adaptive evolution?
natural selection
what is essential to have in a population in order for evolution to occur
variation in heritable traits
- you get variation from different genes
- you need a gene to make a certain protein which causes a phenotype
- if you don’t have the gene to a trait then you can’t have the trait
Both ____ and _____ characters contribute to variation within a population
- discrete
- quantitative
true or false:
discrete characters can be classified on an either - or basis
true
true or false:
quantitative characters vary along a continuum within a population
true
average heterozygosity
measures the average percent of loci that are heterozygous in a population
how is nucleotide variability measured?
measured by comparing the DNA sequences of pairs of individuals
geographic variation
most species exhibit this.
-differences between gene pools of separate populations
cline
which is a graded change in a trait along a geographic axis
how can new genes and alleles arise?
by mutation or gene duplication
what is a mutation?
a change in nucleotide sequence of DNA
only mutations in cells that produce _____ can be passed to offspring
gametes
what is a point mutation
a change in one base in a gene
what are the possible effects of point mutations?
- can be harmless
- mutations in a genes can be neutral because of redundancy in the genetic code
- result in a change in protein production are often harmful
- result in a change in protein production that can sometimes be beneficial
what type of chromosomal mutations are typically harmful?
mutations that delete, disrupt, or rearrange many loci
what type of chromosomal mutations are less harmful?
duplication of small pieces of DNA increases genome size and is usually less harmful
what can shuffle existing alleles into new combinations?
sexual reproduction
population
a localized group of individuals capable of interbreeding and producing fertile offspring
gene pool
consists of all the alleles for all loci in a population
how is a locus fixed?
if all individuals in a population are homozygous for the same allele
how can frequency of an allele in a population be calculated for diploid organisms
p + q = 1
what is the hardy-weinberg principle
- describes a population that is not evolving
- frequencies of alleles and genotypes in a population remain constant from generation to generation
if a hardy weinberg equation is not in equilibrium what does this mean?
-if a population does not meet the criteria of the Hardy-Weinberg principle, it can be concluded that the population is evolving
what equation is used to find the genotypic ratio of alleles?
p^2 + 2pq + q^2 =1
- p is dominant
- 2pq is heterozygous
- q is recessive
what does the hardy weinberg theorem describe?
a hypothetical population that is not evolving
FYI in real populations, allele and genotype frequencies do change over time
what five conditions have to occur for nonevolving populations?
- No mutations
- random mating
- no natural selection
- extremely large population size
- no gene flow
true or false:
natural populations can evolve at some loci, while being in Hardy-weinberg equilibrium at other loci
TRUE
what three major factors alter allele frequencies and bring about most evolutionary change:
- natural selection
- genetic drift
- gene flow
genetic drift
describes how allele frequencies fluctuate unpredictably from one generation to the next
what does genetic tends to reduce what?
genetic variation through losses of alleles
the smaller a sample of population, the greater the chance of____
deviation from a predicted result
founder effect
occurs when a few individuals become isolated from a larger population
-allele frequencies in the small founder population can be different from those in the larger parent population
bottleneck effect
a sudden reduction in population size due to a change in the environment
-the resulting gene pool may no longer be reflective of the original population’s gene pool
if the population remains small, it may be further affected by ______
genetic drift
what are 4 things to know about genetic drift?
- significant in small populations
- causes allele frequencies to change at random
- can lead to a loss of genetic variation within populations
- can cause harmful alleles to show up
gene flow
consists of movement of alleles among populations
-alleles can be transferred through the movement of fertile individuals or gametes
gene flow tends to reduce ______
variation among populations over time
gene flow can decrease _____
the fitness of a population
gene flow can increase____
the fitness of a population
evolution by natural selection involves both _____ and ______
- change
- sorting
new genetic variations arise by _____
chance
beneficial alleles are sorted and favored by
natural selection
how does natural selection bring about adaptive evolution
acting on an organism’s phenotype
what does survival of the fittest really mean?
reproductive success
relative fitness
the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
-selection favors certain genotypes by acting on the phoenotypes of certain organisms
directional selection
favors individuals at one end of the phenotypic range
disruptive seleciton
favors individuals at both extremes of the phenotypic range
stabilizing seleciton
favors intermediate variants and acts against extreme phenotypes
natural selection increases _____
frequencies of alleles that enhance survival and reproduction
sexual selection
natural selection for mating success
sexual dimorphism
marked differences between the sexes in secondary sexual characteristics
intrasexual selection
competition among individuals of one sex for mates of the opposite sex
(usually males)
intersexual selection
often called mate choice, occurs when individuals of one sex are choosy in selecting their mates (usually females)
neutral variation
genetic variation that does not confer a selective advantage or disadvantage
how does diploidy maintain genetic variation?
in the form of hidden recessive alleles through heterozygotes
balancing selection
occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a populations
what does balancing selection include?
- heterozygote advantage
- frequency-dependent selection
heterozygote advantage
occurs when heterozygotes have a higher fitness than do both homozygotes
-natural selection will tend to maintain two or more alleles at that locus
frequency dependent selection
the fitness of a phenotype declines if it becomes too common in the population
-selection can favor whichever phenotype is less common in a population
why can natural selection not fashion perfect organisms? (4)
- selection can only act on existing variations
- evolution is limited by historical constraints
- adaptations are often compromises
- chance, natural selection, and the environment interact
