Modern Synthesis Flashcards
EVOLUTION
Changes in gene frequencies in populations between generations
MODERN SYNTHESIS
The synthesis of genetics and Darwinian evolutionary theory
Explained how inheritance works
CONTINIOUS VARIATION
Traits exhibit a smooth, gradational range of phenotypes within a population, rather than falling into distinct, discrete categories
Fewer individuals show extreme values
Phenotypic variation in which there is a continuum.
ENVIRONMENTAL VARIATION
- Phenotypes will be affected differently by development and environment
- Explains blending of phenotypes without blending genotypes
FORCES OF EVOULTION
- natural selection
- mutation
- gene flow
- genetic drift
NATURAL SELECTION
Reduces variation; removes disadvantageous phenotypes (with their underlying genotypes)
MUTATION
Increases variation through the creation of new variants
GENE FLOW
Maintains variation and can introduce new variants into a population (but it doesn’t create variation, just moves it around)
GENETIC DRIFT
- Changes allele frqequencies through chance, usually decreasing variation
- Unpredictable evolution due to small isolated populations and sampling variation
- Isolated populations become genetically different from one another (variation increases among
populations) - Can result in fixation (all individuals have identical alleles at a locus)
- Causes random fluctuations in genetic frequencies in small populations
EVOLUTIONARY CONSTRAINTS
- A factor limiting the adaptive potential of the
phenotype - A limit on the direction, nature, rate and
amount of evolutionary change that is possible
THREE TYPES OF EVOLUTIONARY CONSTRAINTS
1) Historical constraints
2) Developmental/genetic constraints
3) Material constraints
HISTORICAL CONSTRAINTS
- The adaptative potential of a population depends on the evolutionary history of that population
- Genetic drift
- Disequilibrium
- Local and global optimal adaptations
FOUNDER EFFECT
The establishment of a new population by a small number of original parents, who carry only a fraction of the total genetic variation in the parental population
Genetic diversity is reduced
DISEQUILIBRIUM
- There is an imbalance or deviation from stable, balances condition
- A formerly adaptive trait becomes maladaptive
- Selection produces optimal adaptations only at equilibrium
-
LOCAL OPTIMA
- Best solution in a limited region
- Good but not necessarily the best overall
- Once reached, cannot get to another optimum without steps that reduce fitness
GLOBAL OPTIMA
- Best solution across the entire space
- The best adaptation possible
PLEIOTROPY
- One gene influences two or more seemingly unrelated phenotypic traits
- Causes certain characters to be
correlated
DEVELOPMENTAL CONSTRAINTS
Variation caused by normal genetic and developmental processes (males do not lactate because this ability would likely make them sterile)
MATERIAL CONSTRAINTS
Limitations on adaptation due to the laws of physics and chemistry (gravity and fluid dynamics)
E.g. an elephant cannot be as agile as a mouse because it is physically impossible due to its size
CORRELATED CHARACTERS
- When individuals that have particular variants of one character also tend to have particular variants of a second character
MODERN SYNTHESIS SOLVES THE REMAINING PROBLEMS IN DARWIN’S THEORY:
Mechanism of inheritance:
* Discontinuous (e.g. Mendelian traits)
* Continuous (multi-locus or polygenic traits)
Maintenance/generation of variation:
* Mutation
* Recombination
* Sexual reproduction
