Chapter twenty three: the evolution of population

Q1:what's the difference between microevolution and macroevolution?

A1:microevolution is the change in allele frequencies in a population over generations. macroevolution is the broad pattern od evolution over long spans.

Q2: why is this chapter focus on population?

A2:the evolutionary impact of natural selection is only apparent in the changes in a population of organisms over time.

Q3:what are the main mechaisms that can cause allele frequenct change?

A3: natural selection, genetic drift, and gene flow.

Five Facts:

1. mutation and sexual reproduction produce the genetic variation that makes evolution possible

2. the hardy-weinberg equation can be used to test whether a population is evolving

3. natural selection, genetic drift, and gene flow can alter allele frequencies in a population

4. natural selection is the only machanism that consistently causes adaptive evolution

5. the evolutionary impact of natural selection is only apparent in the changes in a population of organisms over time.

Figure:

the bottleneck effect: a sudden change in the environmrnt, such as a fire or flood, may drastically reduce the size of a population.



Summary:

The population evolved, not its individual members. Characters that vary within a population may be discrete or quantitative. Discrete characters are determined by a single gene locus with different allels that produce distinct phenotypes. Most are quantitative characters,which vary along a continoum within a population. Average heterozygosity is the average percant of loci that are heterzygous. Geographic variation is the differences in the genetic composition of separate populations. Cline is a graded change in a character along a grographic axis. A population is a group of individuals of teh same species that live in the same area and interbreed producig fertile offspring. Gene pool consists of all the alleles for all the loci in all individuals of the population. Hardy-Weinberg principlestates that frequenceies of alleles and genotypes in a population will remain constant from generation to generatrion, provided that only Mendelian segregation and recombination of alleles are at work. p is dominant allele; q is recessive allele. p+q=1; p2+2pq+q2=1. Five condidtions:1no mutation 2random mating 3no matural selection 4extremely large population size 5 no gene flow
Natural selection , genetuic drift, and gene flow can alter alllele frequenceies in a population. Indicviduals in a population exhibit variations in their hertable traits, and those with traits that are better suited to their environmnet tend to produce more offspring than those with traits that are less well suited. Also cause adaptive evolution. Genetic drift os chance events can also cause allele frequenciesto fluctuate unpredictably from one generation to the next, especially in small populationa. Founder effect is when a few individuals become isolated from a large population, this small group may establish a new population whose gene pool differs from the source populations. Gene flow is the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes. Relative fitness is the contribution an individual makes to the gene pool of the next generation, relative to the contibutions of other individuals.

Video:
http://www.youtube.com/watch?v=RtIQvkQWTZY