Midterm Exam Study Guide

What does VISTA stand for?

Variation, Inheritance, Selection, Time, and Adaptation

Gene flow

• Consists of the movement of alleles among populations

• Can increase or decrease fitness

• Alleles can be transferred through the movement of

  fertile individuals or gametes (for example, pollen)

• Ends to reduce variation among populations over time

Founder Effect

Bottleneck Effect

Types Of Speciation

• Allopatric

• Sympatric

Allopatric speciation

Gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

Sympatric speciation

Speciation takes place in geographically overlapping populations

End of the Ordovician

444 mya) – 86% species loss – short, severe ice age

Late Devonian

375 mya) – 75% species loss – land plants (stirred up nutrients?)

End of the Permian

251 mya) – 96% species loss – “The Great Dying” – cataclysmic eruption

End of Triassic

(200 mya) – 80% species loss – Why???????

End of Cretaceous

(66 mya) – 76% species loss -asteroid

Endosymbiont theory

• Proposes that mitochondria and plastids (chloroplasts and related organelles) were formerly small prokaryotes living within larger host cells

• a cell that lives within a host cell

Basal taxon

diverges early in the history of a group and originates near the common ancestor of the group

Sister taxa

groups that share an immediate common ancestor

Clade

• a group of species that includes an ancestral species and all its descendants

• can be nested in larger clades, but not all groupings of organisms qualify as clades

Monophyletic

signifying that it consists of the ancestor species and all its descendants

Paraphyletic

grouping consists of an ancestral species and some, but not all, of the descendants

Polyphyletic

grouping includes distantly related species but does not include their most recent common ancestor

Outgroup

• is a species or group of species that is closely related to the ingroup, the various species being studied

• differentiate between shared derived and shared ancestral characteristics

• a group that has diverged before the ingroup

Homology (Homologous)

• is similarity due to shared ancestry

• Bat and bird wings are homologous as forelimbs

• The more elements that are similar in two complex structures, the more likely it is that they are homologous

Analogy (Analogous)

• is similarity due to convergent evolution

• Bat and bird as functional wings

Types of reproductive isolation

• Prezygotic barriers (Habitat Isolation, Temporal Isolation, Behavioral Isolation, Mechanical Isolation, and Gametic Isolation)

• Postzygotic barriers

Prezygotic barriers

Block fertilization from occurring by:

• Impeding different species from attempting to mate

• Preventing the successful completion of mating

• Hindering fertilization if mating is successful

Postzygotic barriers

Prevent the hybrid zygote from developing into a viable, fertile adult

• Reduced hybrid viability

• Reduced hybrid fertility

• Hybrid breakdown

Genetic Drift

1. is significant in small populations

2. can cause allele frequencies to change at random

3. can lead to a loss of genetic variation within populations

4. can cause harmful alleles to become fixed

Directional selection

favors individuals at one extreme end of the phenotypic range

Disruptive selection

favors individuals at both extremes of the phenotypic range

Stabilizing selection

favors intermediate variants and acts against extreme phenotypes

RNA Hypothesis

• Natural selection produced self-replicating RNA molecules

• The first genetic material was probably RNA, not DNA

• The early genetic material might have formed an “RNA world”

• RNA molecules that were more stable or replicated more

  quickly would have left the most descendant RNA molecules