The Origin of Species_Chapter 24

1. What are the prezygotic and postzygotic barriers?

Prezygotic Barriers: habitat isolation, temperol isolation, behavioral isolation, mechanical isolation, and gametic isolation. These barriers impede mating or hinder fertilization if mating does occur. Postzygotic Barriers: Reduced hybrid vialibility, reduced hybrid fertility and hybrid breakdown. These barriers prevent a hybrid zygote from developing into a viable, fertile adult.

2. Allopatric speciation, and sympatric speciation.

In allopatric speciation, gene flow is interrupted when a pop is divided into geographically isolated subpopulations. (an exemple of founder's effect) In sympatric speciation, speciation occurs in pop that live in the same geographic area when chromosomal changes and nonrandom mating reduces the gene flow. In plants, sympatric speciation can result from accidents during cell division that result in extra sets of chromosomes, a mutant condition known as polyploidy. In animals, it may result from gene-based shifts in habitat or mate preference.

video on speciation:

http://www.youtube.com/watch?v=YCoEiLOV8jc&feature=related

3. Gradualism and punctuated evolution.

gradualism proposes that species descended from a common ancestor and gradually diverge more and more in morphlogy as they acquire unique adaptations. punctuated equilibrium is a term used to describe periods of apparent stasis punctuated by SUDDEN CHANGE observed in the fossil record.

5 facts on this chapter:

. reproductive isolation is defined as the existence of biological barriers that impede members of two species from producing viable, fertile hybrids.

. reduced hybrid viability is when a zygote is formed, genetic incompatibility may cause development to cease.

. adaptive radiation occurs when many new specis arise froma single common ancestor. this occurs when a few organisms make their way to new and distant areas.

. polyploid speciation occurs in animals, but not common. in animals sympatric speciation can result from part of the pop switching to a new habitat, food source, or other sources.

. two species mate and produce viable fertile hybrids, but when the hybrids mate their offspring are weak and sterile.

This chapter was fun. I learned the prezygotic and postzygotic barrier that maintain reproductive isolation in natural populations. i learned about different types of speciations.