Unit 7: Topic 10, 11, and 13

Species

a group able to interbreed and produce viable, fertile offspring

Speciation

formation of new species that results in diversity of life forms

Allopatric Speciation

Physical barrier divides population or a small population is separated from main population. Populations are geographically isolated. This prevents gene flow and is often cause by natural disasters.

Sympatric

A new species evolves while still inhabiting the same geographic region as the ancestral species. This is usually due to an exploration of new niche.

Speciation occurs due to

reproductive isolation

Types of reproductive isolation

prezygotic and postzygotic. Both types maintain isolation and prevent gene flow between the populations

Prezygotic barriers

prevent mating or hinder fertilization

5 times of prezygotic barriers

1. Habitat isolation

2. Temporal isolation

3. Behavioral isolation

4. Mechanical isolation

5. Gametic isolation

Habitat isolation

Species live in different areas or they occupy different habitats within the same area

Temporal isolation

species breed at different times of the day, year, or season

Behavioral isolation

unique behavioral patterns and rituals separate species

Mechanical isolation

the reproductive anatomy of one species does not fit with the anatomy of another species

Gametic isolation

proteins on the surface of gametes do not allow for the egg and sperm to fuse

Postzygotic barriers

prevent a hybrid zygote from developing into a viable, fertile adult

3 types of of postzygotic barriers

1. Reduced hybrid viability

2. Reduced hybrid fertility

3. Hybrid breakdown

Reduced hybrid viability

The genes of different parent species may interact in ways that impair the hybrid’s development or survival

Reduced hybrid fertility

A hybrid can develop into a healthy adult, but it is sterile. Usually results due to differences in number of chromosomes between parents

Hybrid breakdown

the hybrid of the first generation may be fertile, but when they mate with a parent species or one another, their offspring will be sterile

Speciation is a bridge between the concepts of

microevolution and macroevolution

Microevolution

change in allele frequencies within a single species or population (natural and sexual selection, genetic drift, gene flow)

Macroevolution

large evolutionary patterns (adaptive radiation, mass extinction)

Stasis

no change over long periods of time

Evolution and Speciation can occur at

different speeds

Punctuated equilibrium

when evolution occurs rapidly after a long period of stasis

Gradualism

when evolution occurs slowly over hundreds, thousands, or millions of years

Divergent evolution

groups with the same common ancestor evolve and accumulate differences resulting in the formation of a new species

Adaptive radiation

if a new habitat or niche becomes available, species can diversify rapidly

Convergent evolution

two different species develop similar traits despite having different ancestors. Analogous traits

Extinction

the termination of a species. 5 have happened in history. Anytime there is ecological stress, extinction rates can quicken. If a species does go extinct, it opens up a niche that can be exploited by a different species.

Earth was created

4.6 billion years ago

Early earth was not suitable for life until

3.9 bya

Earliest fossil found

in 3.9 bya. cyanobacteria

Early earth

contained inorganic molecules. These could have synthesized organic molecules due to free energy and abundant oxygen

Oparin and Haldane

hypothesized that early Earth was primarily composed of hydrogen, methane, ammonia and

water

Stanley Miller and Harold Urey tested the hypothesis in their lab

They found organic compounds and amino acids formed

Miller and Urey hypothesized that

the organic molecules that formed served as the

building blocks for macromolecules

RNA World Hypothesis

proposes that RNA could have been the earliest genetic material. Helps to explain the pre-cellular stage of life.