Evolution AP Biology Unit 4

History of Evolutionary Theory Linnaeus Developed a system of classification based on body structures (morphology) Lamarck Said species could “will” themselves to change Images taken without permission from http://65.107.211.206/victorian/science/lamarck.jpg and http://www.necsi.org/projects/evolution/lamarck/lamarck/giraffes.jpg

History of Evolutionary Theory Darwin Natural Selection causes species to change Mendel Genetics – now used as another way to look at evolution Img Src: http://www.panspermia.org/darwin.jpg

Natural Selection 5 parts: Population growth has the ability to be exponential. Populations tend to be stable in size (despite #1). Resources are limited. Individuals vary in phenotype. 5. Much phenotypic variation is heritable. Img Src: http://www.abc.net.au/nature/parer/img/galapagos.gif

Natural Selection (in summary) There are more individuals produced than the environment can support  leads to competition for resources. Individuals with advantageous traits in this competition will survive to reproduce and pass on those advantageous traits to the next generation.  

Artificial Selection Breeding animals or plants to have the desired traits Ex. Dog & Cat breeds American curl cat Shar-Pei Great Dane Images taken without permission from http://www.caine.de.rasa.ham.8m.com/images/shar_pei.jpg, http://www.petsmart.com/aspca/images/dogs/great_dane.jpg, http://www.cfainc.org/breeds/profiles/articles/acurl.html ,

Newer developments in Artificial Selection Cocker spaniel + poodle = Cockapoo Labrador + Poodle = Labradoodle Why mix with poodles? Their fur tends to shed less– they were originally bred in an effort to create a guide dog for people who were allergic to dogs.

Vestigial Structures Structures that are no longer used in an organism Ex. Appendix, tail bone Many structures present in embryos are also used to show common ancestry -- developmental biology Img Src: http://www.vh.org/adult/provider/anatomy/AnatomicVariants/SkeletalSystem/Images/19.html

A fictional vestigial structure 

Analogous Structures Similar functions, different structures Indicates different ancestors Ex. Bird wing, butterfly wing Result from convergent evolution: similar selection pressures cause similar structures to evolve.

Homologous structures Similar structure, different functions Indicate a common ancestor Ex. Human hand, seal flipper, bat wing

Biogeography Study of distribution of organisms (past and present) Demonstrate that organisms can evolve similarly to one another in similar environments from different ancestors Ex. Marsupials in Australia – they are only found in Australia but some share similar characteristics with other organisms

Genetic Drift Changes in the gene pool caused by random events Examples: Bottleneck Effect, Founder Effect, Geographic Isolation

Bottleneck Effect drastic reduction in population (due to natural disasters, predators, etc.)

Example of Bottleneck Effect: Pingapalese People example...Pingelapese people of Eastern Caroline islands in Micronesia....5% of currrent population of 3000 have certain type of colorblindness (complete colorblindness) (autosomal recessive)....elsewhere in world it is 1 in 50,000-100,000.  Prevalence can be attributed to a typhoon in 1775 where only 20 people survived and population was inbred from those remaining 20 people. A small region on chromosome 8 is the location of the achromatopsia gene. This gene—CNGB3—is responsible for the defective response of the cones, which are the color-detecting photoreceptors of the eye. Img Src: http://www.genomenewsnetwork.org/articles/06_00/pingelapese_colorblind.shtml Img Src: http://www.7blueseas.com/destinations/images/map_southpacific.jpg

Example of Bottleneck Effect: Cheetahs another example...cheetahs....until 10,000 yrs ago they were more prevalent.  Now, the remaining few thousand are very similar genetically and can be attributed to two bottlenecks...one at the end of most recent ice age and one when they were hunted in 1800's.  Genetic diversity is gone...will suffer from recessive problems. Img Src: http://www.meerkats.com/images/cheetah-cub.jpg Img Src: http://easyweb.easynet.co.uk/~iany/patterns/images/cheetah.jpg

Founder Effect A few individuals become isolated from the original population The resulting population is not representative of the original population

Example of Founder Effect blood typing of native north american population...look at south america...90-100% have type O...could be attributed to founder effect

Another Example of Founder Effect: Ellis-van Creveld Syndrome Amish people...small population that has a high incidence of certain traits...ex...Ellis-van Creveld Syndrome (short-limbed dwarfism, extra fingers, heart disease, teeth at birth and fused bones)...occurs in 7% of births. Img src: http://www.emedicine.com/ped/images/296682EVC-polydactylya.jpg Img Src: http://www.emedicine.com/ped/topic660.htm

Geographic Isolation When physical separation/isolation results in the formation of new species Is a cause of founder effect Adaptive radiation = many species evolving from one original ancestor Example: when a group of American finches colonized the Hawaiian islands, the group became geographically isolated from other populations of the species. these finches eventually gave rise to the 23 species of Hawaiian honeycreepers.->adaptive radiation

Example of Geographic Isolation Example 2: Geologic evidence from a study of wave patterns in sedimentary rocks indicates that most of Death Valley was covered by a huge lake during the last ice age. When the ice age ended, the region became dry. Only small, spring fed ponds remained. Members of a fish species that previously formed a single population in the lake may have become isolated in different ponds. The environments of the isolated ponds differed enough that natural selection and perhaps genetic drift acted on the separate populations Img Src: http://www.desertfishes.org/na/cyprinod/cyprinod/cssalinu/cssalin1.jpg

Gene Flow · Migration (immigration, emigration) Breeding across prior barriers (cultural barriers, for instance, as in human populations) Changes allelic frequencies Ex. Human migration

Phenotypic Polymorphism Defined as variety of physical traits Due to genetic variation genetic polymorphism nonheritable variation

Fitness ·  fitness = contribution of individual to gene pool, relative to others’ contributions ·  relative fitness = contribution of a genotype (all individuals alike) ·  fitness of 1 means you (or your genotype) contribute at a maximum (100%) fitness of 0 means you (or your genotype) do not reproduce at all

Types of Selection Selection = Environment chooses those with the best adaptations to survive

Stabilizing Selection = middle phenotype is selected for

Disruptive Selection The two extremes are selected for Ex. Snails marine snails...white and tan....tan ones can live among white barnacles on tan rocks, tan ones can live on tan rocks

Directional Selection = one phenotype is selected for Img Src: http://web.nmsu.edu/~wboeckle/pepper_moth2.JPG Industrial melanism

Heterozygote Advantage When being heterozygous gives you an advantage Explains why a harmful recessive allele does not get eliminated from a population Ex. Sickle cell anemia – heterozygotes are resistant to malaria Img Src: http://www.nidcd.nih.gov/news/releases/02/malaria.jpg Img Src: http://www.unomaha.edu/~swick/images/sickel.jpg

Sexual Selection Genders appear different due to Sexual Dimorphism Competition is inter- and intragender specific Ultimately has to do with competition for higher fitness

Constraints on Natural Selection Populations are not perfectly suited to their environments because Environments constantly change and offer new challenges– individuals present might not have been the ones who would be best suited (Ex. A new population of people marooned from a breaking ship begin a new population. They do not necessarily represent the best of the gene pool)

Constraints on Natural Selection Populations are not perfectly suited to their environments because Evolution is slow and dramatic new structures rarely form/appear; instead, old structures are used for new structures (Ex. Birds have 2 wings rather than 4, which could help with flight, because they evolved from a 4-appendage reptile; 2 wings and 2 legs)

Constraints on Natural Selection Populations are not perfectly suited to their environments because Adaptations are often compromised (Ex. seal legs would help in land motion, but swimming with legs is less efficient than with flippers)

Constraints on Natural Selection Populations are not perfectly suited to their environments because Natural selection can only pick the best variation—it can’t create variations