General Biology: Evolution, Genetics, and Natural Selection Study Guide

Biological Hierarchy and Taxonomy

Taxonomic Ranks

Taxonomy is the science of classifying living organisms into hierarchical groups based on shared characteristics.

• Order, class, and taxon are all specific taxonomic ranks.

• Order is a rank below class and above family.

• Taxon refers to any group or rank in a biological classification.

Characteristics of Living Things

Defining Life

All living things share certain fundamental characteristics.

• Reproduction: Organisms replicate themselves.

• Metabolism: Organisms make their own food out of inorganic compounds or obtain energy from other sources.

• Cellular Organization: Organisms are made up of one or more cells.

The Scientific Method

Nature of Scientific Theories

A scientific theory is a comprehensive explanation for a broad set of phenomena, supported by a wide body of evidence.

• Scientific theories are not guesses; they are well-substantiated explanations.

• They are supported by repeated testing and evidence.

Controlled Experiments

Controlled experiments are essential for testing hypotheses in science.

• They include at least two groups: one that receives the experimental treatment and one that does not (the control group).

• All other variables are kept constant to ensure reliable results.

Hypothesis Formation

Formulating a hypothesis and making testable predictions are key steps in the scientific method.

• Hypothesis: A proposed explanation for an observation, which can be tested.

• Predictions are made based on the hypothesis and tested through experiments or observations.

Evolution and Natural Selection

Variation and Population Genetics

Variation within populations is a fundamental concept in evolution.

• Variation: Differences in traits among individuals in a population.

• Natural selection acts on this variation, leading to evolutionary change.

Lamarckian Inheritance

Lamarck proposed that traits acquired during an organism's lifetime could be passed to offspring, a concept now largely discredited.

• He suggested that as an individual develops, its phenotype changes in response to environmental challenges, and these changes are inherited by offspring.

Uniformitarianism

The concept that geological processes occurring now have always operated in the past at similar rates.

• "The forces acting on the Earth were the same in the past as present."

Spontaneous Generation

The disproven idea that living organisms can arise from nonliving matter.

• Experiments by Redi and others showed that maggots only appeared in meat when flies could lay eggs on it.

Homology and Analogy

Homologous structures are anatomical features that are similar due to shared ancestry.

• Example: The forelimbs of humans, horses, birds, and bats.

Transitional Features

Traits that are intermediate between ancestral and derived forms, providing evidence for evolution.

• Example: Fossil species showing the transition from land mammals to whales.

Fitness

Fitness refers to an individual's ability to survive and reproduce relative to others in the population.

Postulates of Natural Selection

Darwin's theory of natural selection is based on several key postulates:

• Survival and reproductive success are variable among individuals.

• Variation in traits is heritable.

• More offspring are produced than can survive.

• Individuals with advantageous traits are more likely to survive and reproduce.

Novelty in Darwin and Wallace's Theory

They emphasized the importance of variation in populations and that natural selection acts on this variation.

Natural Selection

Natural selection can favor beneficial mutations, leading to adaptation.

• It does not create mutations, but acts on existing variation.

• It is not a random process; it is driven by differential survival and reproduction.

Selection Types

• Directional selection: Favors one extreme phenotype.

• Stabilizing selection: Favors intermediate phenotypes, reducing variation.

• Disruptive selection: Favors both extreme phenotypes over intermediates.

Genetic Drift

Genetic drift is a random change in allele frequencies, more pronounced in small populations.

Assortative Mating

When individuals mate with others that are similar (or dissimilar) in certain traits.

Hydrolysis

Hydrolysis is a chemical reaction that breaks a molecule using water.

• $\text{AB} + \text{H}_2\text{O} \rightarrow \text{A} + \text{B}$

Population Genetics and Hardy-Weinberg Equilibrium

Alleles and Genotypes

• Allele: A version of a gene.

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits of an organism.

Hardy-Weinberg Principle

The Hardy-Weinberg equilibrium describes a non-evolving population where allele and genotype frequencies remain constant.

• $p^2 + 2pq + q^2 = 1$

• $p + q = 1$

• Where p is the frequency of the dominant allele, and q is the frequency of the recessive allele.

Calculating Allele Frequencies

• Given genotype frequencies, allele frequencies can be calculated using the Hardy-Weinberg equations.

• Example: If 9% of plants are homozygous recessive ($q^2 = 0.09$), then $q = 0.3$.

Evolutionary Mechanisms

Gene Flow, Mutation, and Polyploidy

• Gene flow: Movement of alleles between populations.

• Mutation: Source of new genetic variation.

• Polyploidy: Having more than two sets of chromosomes, common in plants.

Ecological Niche

An ecological niche is the range of resources a species can use and the range of conditions it can tolerate.

Reproductive Isolation and Speciation

• Reproductive isolation: The primary criterion for defining species boundaries in the biological species concept.

• Allopatric speciation: Speciation due to geographic separation (vicariance event).

• Sympatric speciation: Speciation without geographic separation, often via polyploidy in plants.

Prezygotic and Postzygotic Barriers

• Prezygotic barriers: Prevent mating or fertilization between species (e.g., habitat isolation, temporal isolation, gametic isolation).

• Postzygotic barriers: Prevent hybrid offspring from surviving or reproducing.

Misconceptions in Evolution

• Evolution is not goal-oriented; it does not strive toward "higher" forms.

Tables

Summary Table: Types of Selection

Type of Selection	Description	Example
Directional	Favors one extreme phenotype	Gal fly size favoring larger galls
Stabilizing	Favors intermediate phenotypes	Human birth weight
Disruptive	Favors both extremes over intermediates	Beak size in certain birds

Summary Table: Reproductive Barriers

Barrier Type	Mechanism	Example
Prezygotic	Prevents mating/fertilization	Habitat isolation, temporal isolation
Postzygotic	Prevents hybrid viability/fertility	Hybrid sterility

Summary Table: Hardy-Weinberg Variables

Symbol	Meaning
p	Frequency of dominant allele
q	Frequency of recessive allele
p^2	Frequency of homozygous dominant genotype (AA)
2pq	Frequency of heterozygous genotype (Aa)
q^2	Frequency of homozygous recessive genotype (aa)

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard General Biology curriculum.