chapter 24. the origin of species

Q. what is allopatric speciation?

gene flow is interrupted when a population is divided into geographically isloated subpopulations.

Q.what is phylogenetic species concept?

it defines a species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.

Q. what is an allopolyploid?

they are fertile when mating wich each other but cannot interbreed with either parent species

facts

1.Temporal isolation prevents fertilization because the two different species reproduce at different times.

2.Mechanical isolation acts a prezygotic barrier by preventing sexual intercourse between two different species.

3.Prezygotic and postzygotic isolating mechanisms have preserved the integrity of the different species throughout millions of years.

4.Behavioral isolation is another isolating mechanism. This mechanism operates through courtship behavioral patterns. If one species displays a certain courtship pattern, it won’t be recognized by those of the other species.

5.Hybridization is the practice of two different species interbreeding.

diagram

A region in which members of different species meet and mate, producing at least some offspring of mized ancestry. a hybrid zone is like observing a natural experiment on speciation. Will the result be the rapid formation of a new species.

video

http://www.youtube.com/watch?v=tx8C3pq4poE

summary

The biological species concept is the most widely accepted species concept. It defines species in terms of interbreeding. For instance, Ernst Mayr defined a species as follows: "species are groups of interbreeding natural populations that are reproductively isolated from other such groups."The biological species concept explains why the members of a species resemble one another, i.e. form phenetic clusters, and differ from other species.When two organisms breed within a species, their genes pass into their combined offspring. As this process is repeated, the genes of different organisms are constantly shuffled around the species gene pool. The shared gene pool gives the species its identity. By contrast, genes are not (by definition) transferred to other species, and different species therefore take on a different appearance. This explanation should be compared with that given by the ecological species concept.