2MICROEVOLUTION Population -- all the members of a single species Population genetics – studies variations in alleles in gene pools*Basically, microevolution studies small changes in alleles that occur within a population. Over time, these small changes can accumulate, resulting in major differences within the population. Dogs have been artificially selected for certain traits, resulting in a wide range of breeds with very different characteristics*
4Gene pool – total of all the allele in the population Alleles – chromosome sections that code for specific proteins traitsExamples: Humans have alleles forblue eyes / brown eyes /green eyes curly/straight hairblood type A / B / O / AB
5Industrial MelanismAs trees became darker due to industry, darker moths had a better chance of survival. Over time, more darker alleles were present in the population.
6Natural selection – the peppered moth Peppered moths on tree trunk
7A. Causes of Microevolution 1. Genetic MutationsPolymorphism : two or more distinct phenotypes ex blood types, eye color..etcMutations (can be harmful or beneficial)Some mutations may at first appear harmful, but give an advantage if the environment changes. -- this is referred to as RELATIVE FITNESS
9Does gene flow increase or decrease diversity? movement of alleles among populations, by migration, increases variationCan prevent speciation from occurringDoes gene flow increase or decrease diversity?
10Example of GENE FLOWEach rat snake represents a separate population of snakesThese snakes remain similar and can interbreedThis keeps their gene pools somewhat similarThey are considered subspecies
11Which populations do you think are the LEAST similar? Figure 18.3Which populations do you think are the LEAST similar?Why?
123. Mating. a. Random mating is pairing by chance. b 3. Mating a. Random mating is pairing by chance b. Nonrandom mating – individuals choose their mates Which method of mating do humans use?Can you think of any organisms that mate randomly?
13Assortative mating occurs when individuals mate with those that have the same phenotype. Does this increase or decrease the diversity in the population?
14This results in some extreme characteristics. Sexual selection occurs when males compete for the right to reproduce and the female selects males of a particular phenotype. (guppies, lions)This results in some extreme characteristics.Sexual dimorphism - when males and females of a species look different.
15GENETIC DRIFTRefers to changes in allele frequencies of a gene pool due to chance.It is more obvious in small populations.
16Bottleneck Effect – caused by a severe reduction in population (possibly a Natural disaster), reduces overall diversity.
17Cheetahs have very little diversity in their gene pool due to bottleneck
18FOUNDER EFFECTThe founder effect is an example of genetic drift where rare alleles or combinations occur in higher frequency in a population isolated from the general population.EX: Dwarfism in Amish communities Due to few German founders
19Five in Five, Five Words or Less 1. Gene Pool2. Microevolution3. Gene Flow4. Phenotype5. Genetic Drift
20MACROEVOLUTION Evolutionary change at or above the species level Speciation – the splitting of one species into two or more species
21What is a Species?A group of actually or potentially interbreeding populations (isolated from other groups)
22Hybrids occur when members of different species produce offspring... Lion + Tiger = LigerTiger + Lion = Tigon
24SPECIATION Flycatcher species Empidonax minimus Empidonax virescens Empidonax tralliWhat stops these species from mating with each other? (their DNA allows them to)
25What would happen if two of these birds did mate? Figure 18.10cEach species has a unique song and each species occupies a different habitat during mating season. What would happen if two of these birds did mate?
26MODES OF SPECIATION 1. Allopatric Speciation Populations separated geographicallyb. Variations accumulateAberts squirrel (south rim)Kaibab squirrel (north rim)
272. SYMPATRIC SPECIATIONSympatric speciation would occur when members of a single population develop a difference without geographic isolation.Ex. Apple maggot flyHawthorn Fruit, Apple Fly: Introduction of the apple to N. America led to the development of the Apple Fly. Apple Flies feed mainly on Apples and Hawthorn flies feed mainly on Hawthorn Fruit even if they are in the same orchard. Adults look identical and there is no geographical separation.