Chapter 23 Flashcards
Natural selection acts on the
individuals
The effects of natural selection
evolution
effects (evolution) of natural selection are seen at the
population level
Genetic variation
differences among individuals in the composition of their genes or other DNA sequences
differences among individuals in the composition of their genes or other DNA sequences
Genetic variation
Genetic code (genotype)
determines the physical expression of a trait (phenotype)
determines the physical expression of a trait (phenotype)
Genetic code (genotype)
What plays a role in phenotypic expression?
Environment
What is a product of genotype and environmental factors
Phenotype
What is phenotype the product of?
The product of genotype and environmental factors
Sources of genetic variation
- Formation of new alleles
- Altering gene number or position
- Rapid reproduction
- Sexual reproduction
Mutations
change the nucleotide sequence
change in the nucleotide sequence
mutations
Mutations that result in new phenotypes tend to be…
maladaptive and are removed by natural selection
What are harmful recessive traits masked by?
heterozygote protections
Where do neutral mutations occur?
in non-coding regions (neutral variation)
Redundancy of genetic code
a source of neutral variation
a source of neutral variation
redundancy of the genetic code
Population
a group of organisms of the same species occurring in the same place at a given time
a group of organisms of the same species occurring in the same place at a given time
population
Microevolution
change in allele frequencies in a population over generations
change in allele frequencies in a population over generations
Microevolution
Where does microevolution occur?
The population level
What causes adaptive evolution
natural selection
genotype
the genetic make up, or set of alleles, of an organism
the genetic make up, or set of alleles, of an organism
genotype
phenotype
the observable physical or physiological traits of an organism (determined by genotype)
the observable physical or physiological traits of an organism (determined by genotype)
phenotype
Gregor Mendel
Austrian monk that determined there are “units” of inheritance (now called genes)
Austrian monk that determined there are “units” of inheritance (now called genes)
Gregor Mendel
Sexual reproduction
shuffles existing alleles into new combinations
Types of sexual reproduction
- Independent Assortment
- Crossing over
- Fertilization
Independent assortment
homologous chromosomes pair up randomly during meiosis (cellular division)
homologous chromosomes pair up randomly during meiosis (cellular division)
Independent assortment
Crossing over
genetic material is swapped (exchanged) during meiosis
genetic material is swapped (exchanged) during meiosis
crossing over
Fertilization
a number of mating opportunities exist within a population, resulting in joining of gametes with genetic background
a number of mating opportunities exist within a population, resulting in joining of gametes with genetic background
fertilization
a population’s genetic make up is characterized by describing its…
gene pool
Gene pool
all copies of every type of allele at every locus in all members of the population
all copies of every type of allele at every locus in all members of the population
gene pool
Fixed allele
occurs if only one allele exists for a particular locus (all individuals are homozygous for the allele)
occurs if only one allele exists for a particular locus (all individuals are homozygous for the allele)
fixed allele
Tthe proportion of each allele in the gene pool?
allele frequency
Allele frequency
the proportion of each allele in the gene pool
Allele frequency remains constant from…
Generation to generation (no evolution)
Conditions for Hardy-Weinberg Equilibrium
- No mutations
- Random mating
- No natural selection
- Extremely large population size
- No gene flow
Mechanisms of evolution
- mutation
- non-random mating
- genetic drift
- gene flow
- natural selection
Mutation (2)
a source of variation
Random with respect to fitness
Mutation
harmful mutations are…
phased out, beneficial alleles increase
Since mutations rarely occur…
there is very little change in allele frequencies from generation to generation
Non-random mating
occurs when individuals mate within a subset of the population
Non-random mating my affect the frequencies of heterozygotes and homozygotes, but…
unless individuals with certain ingerited traits are more likely to obtain mates, allele frequencies are unchanged
Examples of non-random mating
female mate choice and male-male competition
When the probability of mating is not the same among individuals
Non-random mating
Three major factors that alter allele frequencies and bring about most evolutionary changes
- natural selection
- genetic drift
- gene flow
Genetic drift
unpredictable changes in allele frequencies dut to change alone (not by inherited trait)
Genetic drift is random with respect to…
fitness
Genetic drift occurs…
in every population in every generation
Important points about genetic drift
- is random fluctuation in allele frequencies
- removes genetic variation from the population
- more powerful in small populations
Founder Effect
a few individuals become isolated from the source population and differs genetically from the source
Genetic Bottleneck
sudden reduction in population size (catastrophic event) results in drastic change in gene pool
Gene flow
transfer of alleles into or out of a population due to the movement of fertile individuals or gametes
Natural selection
differential success in reproduction results in certain alleles being passed to the next generation in greater proportions
The only mechanism that consistentl causes adaptive evolution
Natural selection
adds variation and can act antagonistically
gene flow
removes variation and may or may not cause an increase in beneficial or harmful alleles
genetic drift
Relative fitness
contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals
Types (modes) of Natural Selection
- Directional selection
- Disruptive selection
- Stabilizing selection
Directional selection
occurs when selection favors one extreme phenotype over another
Disruptive selection
occurs when selection favors extreme phenotypes over intermediate phenotpes
Stabilizing selection
occurs when selection favors intermediate phenotype over the extremes
