Bio196 study guide Flashcards

A scientific theory is a well-substantiated explanation of some aspect of the natural world that is based on a body of evidence and has stood up to repeated testing and scrutiny. It is more robust than a hypothesis and provides a framework for understanding observations and making predictions.

Evolution is the process through which species of organisms change over time through variations in their genetic makeup. These changes can lead to the development of new species.

Descent with modification explains that species change over time, give rise to new species, and share a common ancestor. This concept accounts for the similarities (shared traits from a common ancestor) and differences (adaptations to different environments) among species.

Natural selection is not simply a matter of chance because it involves differential survival and reproduction of individuals due to differences in phenotype. An adaptation is a trait that increases an organism's fitness in its environment. Natural selection is the only mechanism that consistently leads to adaptations because it directly favors traits that enhance survival and reproduction.

Adaptation is a genetic change in a population over generations, while acclimation is a temporary change in an individual organism's phenotype in response to environmental conditions.

Darwin and Wallace's ideas on evolution by natural selection built on earlier ideas about species change but provided a mechanism (natural selection) for how this change occurs.

The four principal requirements for evolution by natural selection are:

1. Variation in traits

1. Differential reproduction

1. Heredity

1. Time

Direct observations, such as changes in beak morphology of medium ground finches on the Galapagos Islands, support these criteria. Similarly, the evolution of antibiotic resistance in bacteria demonstrates these principles.

Homology refers to traits inherited from a common ancestor. Predictions from evolution include similarities in structure, embryonic development, cellular processes, and molecular sequences.

Convergent evolution occurs when unrelated species evolve similar traits independently. Analogous structures are traits that arise from convergent evolution.

The theory of evolution predicts transitional forms in the fossil record and patterns of species distribution that reflect historical connections between landmasses.

Microevolution is the change in allele frequencies within a population over time. The three main mechanisms are natural selection, genetic drift, and gene flow.

Genetic variation is essential for evolution. It is created by mutations, which can be random changes in DNA sequences. Most mutations are neutral or harmful, but some can be beneficial.

Sexual reproduction increases genetic variation through recombination and independent assortment of chromosomes.

A population in Hardy-Weinberg equilibrium has constant allele and genotype frequencies over generations, indicating no evolution. Deviations suggest evolutionary forces at work.

Genetic drift is the random fluctuation of allele frequencies, more pronounced in small populations. The founder effect and bottleneck effect are examples of genetic drift.

Gene flow is the transfer of alleles between populations, which can increase genetic variation within populations and reduce differences between them.

Different modes of selection (directional, stabilizing, disruptive) alter the frequency distribution of traits in a population.

Sexual selection involves traits that increase mating success. Females may prefer males with exaggerated traits as indicators of genetic quality.

Speciation is the formation of new species. The biological species concept defines species based on reproductive isolation. Reproductive isolating mechanisms prevent gene flow between species.

Allopatric speciation occurs through geographic isolation, while sympatric speciation occurs without geographic barriers, often through polyploidy in plants.

Hybrid zones are regions where different species meet and interbreed. Outcomes include reinforcement, fusion, or stability.

Gradual evolution involves slow, steady change, while punctuated equilibria involve rapid bursts of change.

The origin of life likely involved the formation of simple organic molecules, the development of self-replicating RNA, and the emergence of cellular life.

Radiometric dating calculates the age of fossils based on the decay of radioactive isotopes.

Key events include the origin of unicellular and multicellular organisms and the colonization of land.

The five major extinctions significantly impacted life's diversity.

1. End Ordovician (444 million years ago; mya)
2. Late Devonian (360 mya)
3. End Permian (250 mya)
4. End Triassic (200 mya)
5. End Cretaceous (65 mya)

Adaptive radiation is the rapid evolution of diverse species from a common ancestor, often following environmental changes or new opportunities.