The Modern Synthesis

Chapter Study Outline

1. Population Genetics
   1. Frequencies of genotypes give geneticists a description of the genetic composition of a population.
   2. Genotype frequencies can be changed by means of sexual reproduction, natural selection, mutation, and genetic drift. Selection can only produce change when there is variation in the population.
   3. To calculate the effect of sexual reproduction on genotype frequencies, first calculate the allele frequencies of the gene in question, then calculate the genotypes.
   4. If a population is unaffected by forces of evolution, the distribution of genotypes will operate in Hardy–Weinberg equilibrium, denoted with the equation p² + 2pq + q² = 1.
   5. If one phenotype results in better fitness, it will increase in frequency in subsequent generations. The frequency of phenotypes is changed by natural selection, not individual genes or gene frequencies directly.
   6. The organism's environment provides constraints for the strength and direction of selection.
2. The Modern Synthesis
   1. Fisher, Haldane, and Wright showed how Mendelian genetics explain continuous variation. Continuous variation, natural selection, and the work of Dobzhansky, Mayr, and Simpson combined to create what is known today as the modern synthesis.
      1. The expression of phenotypes depends to some extent on environmental variation.
      2. Although selection can deplete variation, mutation can introduce new gene variants.
      3. Hidden variation accounts for cumulative evolutionary change.
3. Natural Selection and Behavior
   1. Both behavior and morphology can be affected by natural selection, as in the example of the soapberry bug, which engages in mate guarding.
   2. Behavioral traits can be found in a wide variety of environments and can allow an organism to adjust its behavior in relation to local conditions.
4. Constraints on Adaptation
   1. The three necessities of evolution are: the character must vary; variation must affect reproductive success; and the variation must be heritable.
   2. Many characters are correlated, either positively or negatively.
   3. Some genes control more than one character and are called pleiotropic.
   4. Sometimes evolutionary changes cause maladaptive responses.
   5. When evolution occurs quickly or the environment changes, populations can be in disequilibrium.
   6. Genetic drift leads to unpredictable evolution that can isolate a population.
   7. Evolution is governed by developmental constraints and the laws of physics and chemistry.