11.1 KEY CONCEPT A population shares a common gene pool.

Transcription

1 11.1 KEY CONCEPT A population shares a common gene pool.

2 Why it s beneficial: Genetic variation leads to phenotypic variation. It increases the chance that some individuals will survive Phenotypic variation is necessary for natural selection.

3 How it s stored in a population Genetic variation is stored in a population s gene pool. made up of all alleles in a population Different allele combinations form when organisms have offspring

4 How it s measured: Allele frequencies measure genetic variation. measures how common an allele is in population can be calculated for each allele in gene pool

5 Genetic variation comes from two main sources. Mutation is a random change in the DNA of a gene. can form new allele can be passed on to offspring if in reproductive cells Recombination forms new combinations of alleles. usually occurs during meiosis parents alleles arranged in new ways in gametes

6 Genetic variation comes from several sources. Hybridization is the crossing of two different species. occurs when individuals can t find mate of own species topic of current scientific research

7

8 11.2 KEY CONCEPT Populations, not individuals, evolve.

9 Natural selection acts on distributions of traits. A normal distribution graphs as a bell-shaped curve. highest frequency near mean value frequencies decrease toward each extreme value A population follows a normal distribution when: that population is not under natural selection for the trait Draw this in your notes

10 Natural selection can change the distribution of a trait in one of three ways. This is called microevolution. It is evolution within a population. There is an observable change in the allele frequencies over time can result from natural selection

11 Natural selection can take one of three paths. Directional selection favors phenotypes at one extreme. Example: drug-resistance in bacteria Draw the solid line in your notes

12 Stabilizing selection favors the intermediate phenotype. Example: size of gall flies Draw the solid line in your notes

13 Disruptive selection favors both extreme phenotypes. Example: body color in bunting birds Draw the solid line in your notes

14 11.3 KEY CONCEPT Natural selection is not the only mechanism through which populations evolve.

15 Gene flow Definition: movement of alleles between populations. How it works: When animals migrate from one population to another and breed in the new population. immigration & emigration Lots of gene between populations keeps populations (genetically) similar. Limited gene flow results in Genetically different populations that could evolve into diff species

16 Genetic drift Definition: change in allele frequencies due to chance. How it works: causes a loss of genetic diversity and is most common in small populations. Key Terms: Bottleneck Effect occurs when an event drastically reduces population size.

17 Founder effect It occurs when a few individuals start a new population. The founder effect is genetic drift that occurs after the start of new population.

18 Genetic drift has negative effects on a population. some individuals can t adapt harmful alleles can become more common due to chance

19 Sexual selection Definition: occurs when certain traits increase mating success. How it works: Sexual selection occurs due to higher cost of reproduction for females. females are more limited in potential offspring each cycle males produce many sperm continuously Females preferentially mate with males that display certain traits

20 There are two types of sexual selection. intrasexual selection: competition among males for a female intersexual selection: males display certain traits to attract females

21

22 11. 5 KEY CONCEPT New species can arise when populations are isolated.

23 The isolation of populations can lead to speciation. Populations become isolated when there is no gene flow. Isolated populations adapt to their own environments. Genetic differences can add up over generations.

24 Reproductive isolation can occur between isolated populations. members of different populations cannot mate successfully final step to becoming separate species Speciation is the rise of two or more species from one existing species.

25

26 Populations can become isolated in several ways. 1. Behavioral barriers can cause isolation. called behavioral isolation includes differences in courtship or mating behaviors

27 2. Geographic barriers can cause isolation. called geographic isolation physical barriers like mountains and rivers divide population

28

29 3. Temporal barriers can cause isolation. called temporal isolation timing of reproductive periods prevents mating

30 11.6 KEY CONCEPT Evolution occurs in patterns.

31 Evolution through natural selection is not random. Natural selection can have direction. The effects of natural selection add up over time.

32 Convergent evolution describes evolution toward similar traits in unrelated species.

33

34 Divergent evolution describes evolution toward different traits in closely related species. red fox Kit fox ancestor How do convergent and divergent evolution illustrate the directional nature of natural selection?

35

36 LE 24-6 A. harrisi A. leucurus

37 Species can shape each other over time. When two or more species evolve together, this is called coevolution. evolutionary paths become connected species evolve in response to changes in each other

38 Coevolution can occur in beneficial relationships. Both species receive benefits from the other as a result of adaptations that each species evolved over many generations The ant lives inside hollow thorns and protects the acacia by stinging any potential predators

39 Coevolution can occur in competitive relationships, sometimes called evolutionary arms races. Both species respond to competitive pressure from the other through adaptations over many generations

40 Species can become extinct. Extinction is the elimination of a species from Earth. Background extinctions occur randomly but at a very low rate. usually affects a few species in a small area caused by local changes in environment

41 Mass extinctions are rare but much more intense. destroy many species at global level thought to be caused by catastrophic events like earthquakes, volcanic eruptions, etc. at least five mass extinctions in last 600 million years

42 Speciation often occurs in patterns. A pattern of punctuated equilibrium exists in the fossil record. theory proposed by Eldredge and Gould in 1972 episodes of speciation occur suddenly in geologic time followed by long periods of little evolutionary change revised Darwin s idea that species arose through gradual transformations

43 Many species evolve from one species during adaptive radiation. ancestral species diversifies into many descendent species descendent species usually adapted to wide range of environments