Chapter 23 Microevolution Flashcards
What is microevolution?
Change of life in allele frequencies in a population over generations
What are the 3 mechanical causes of allele frequency change?
- natural selection
- genetic drift
- gene flow
What can only cause adaptive evolution?
Natural selection
What is a prerequisite for evolution?
Genetic variation in heritable traits
What is genetic variation?
Among individuals it’s caused by differences in genes or other DNA segments
What is a phenotype?
Physical appearance of genes
What is a genotype?
Genetic makeup code
What are some phenotypic differences determined by?
Determined by a single gene
What are other phenotypic differences determined by?
The influence of two or more genes, and varies along a continuum within a population
What is measured as gene variability or nucleotide variability?
Genetic variation
What also can cause a change in phenotypic variation?
Environmental influences
What kind of variation can only have evolutionary consequences?
Only genetically determined variation
When does the recombination of existing alleles happen?
Happens during the process of meiosis
What is a mutation?
Random change in nucleotide sequence of DNA
What is a point mutation?
Change in one base in a gene
What are the effects of a point mutation?
- Varies in mutation can be harmful, beneficial, or neutral
- Usually are hidden in recessive alleles
What is neutral variation?
Conferring no selective advantage or disadvantage in mutation
Where can neutral variation happen?
It can happen in point mutations in the noncoding region
Chromosomal Mutation
Mutations that delete, disrupt, or rearrange many loci that are typically harmful
Duplication Mutation
Increases genome size and is usually less harmful
- can take on new function by further mutation
Why are mutations rates higher in viruses compared to prokaryotes?
Due to rapid reproduction
What is a population?
Localized group of individuals that’s capable of interbreeding and producing fertile offspring
What is a gene pool?
Consists of all the alleles for all loci in a population
What is a diploid organism?
The total number of alleles at locus is the total number of individuals times 2
What is the Hardy-Weinberg formula?
- p + q = 1
- p^2 + 2pq + q^2 = 1
What does the Hardy-Weinberg equation describe?
Describes the genetic makeup we expect for a population that’s not evolving at a particular locus.
How do we know if a population may be evolving?
If the observed genotype of population differs from expectations under Hardy-Weinberg
What is the Hardy-Weinberg Equilibrium?
Alleles and genotype frequencies remain constant from generation to generation
What are the 5 conditions for a nonevolving population that are rarely met?
- no mutations
- random mating
- no natural selection
- extremely large population size
- no gene flow
What is genetic drift?
Describes how allele frequencies fluctuate unpredictably from one generation to the next
- tends to reduce genetic variation thru loss of alleles
What is the founder effect?
Occurs when a few individuals become isolated from a larger population
What is the bottleneck effect?
Sudden reduction in population size due to change in the environment
(such as changes due to natural disasters)
What is relative fitness?
Contribution of an individual makes to the gene pool of the next generation
- relative to the contributions of other individuals
What is gene flow?
Consists of the movement of alleles among populations
What are some effects of genetic drift?
- significant in small populations
- can cause allele frequencies to change at random
- can lead to a loss of genetic variation within populations
- can cause harmful alleles to become fixed
What are some effects of gene flow?
- can increase or decrease the relative fitness of a population
- reduces genetic variation over time
What are the 3 modes of selection?
- directional selection
- disruptive selection
- stabilizing selection
Directonal Selection
favors individuals at one extreme end of the phenotypic range
Disruptive Selection
Favors individuals at both extreme ends of the phenotypic range
Stabilizing Selection
Favors immediate variants and acts against extreme phenotypes
Sexual selection?
natural selection for mating success that results in sexual dimorphism
sexual dimorphism
Marked differences b/w the sexes in secondary sexual characteristics
intrasexual selection
direct competition among individuals of one sex (often males) for mates of the opposite sex
intersexual selection
often called mate choice, occurs when individuals of one sex (usually females) are choosy in selecting their mates
Balancing Selection
Occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population
- includes: heterozygous advantage and frequency dependent selection
Heterozygote Advantage
Occurs when heterozygotes have a higher fitness than do both homozygotes
- results from stabilizing or directional selection
Frequency-Dependent Selection
Fitness of a phenotype declines if it becomes too common in the population
Why natural selection cannot fashion perfect organisms? (4 things)
- selection can act only on existing variations
- evolution is limited by historical constraints
- Adaptations are often compromises
- Chance, natural selection, and the environment interact
