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Chapter 18 - The Process of Evolution

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1 Chapter 18 - The Process of Evolution

2 MICROEVOLUTION 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*


4 Gene pool – total of all the allele in the population
Alleles – chromosome sections that code for specific proteins traits Examples: Humans have alleles for blue eyes / brown eyes /green eyes  curly/straight hair blood type A / B / O / AB

5 Industrial Melanism As trees became darker due to industry, darker moths had a better chance of survival. Over time, more darker alleles were present in the population.

6 Natural selection – the peppered moth
Peppered moths on tree trunk

7 A. Causes of Microevolution
1. Genetic Mutations Polymorphism : two or more distinct phenotypes ex blood types, eye color..etc Mutations (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


9 Does gene flow increase or decrease diversity?
movement of alleles among populations, by migration, increases variation Can prevent speciation from occurring Does gene flow increase or decrease diversity?

10 Example of GENE FLOW Each rat snake represents a separate population of snakes These snakes remain similar and can interbreed This keeps their gene pools somewhat similar They are considered subspecies

11 Which populations do you think are the LEAST similar?
Figure 18.3 Which populations do you think are the LEAST similar? Why?

12 3. 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?

13 Assortative mating occurs when individuals mate with those that have the same phenotype. 
 Does this increase or decrease the diversity in the population?

14 This 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.

15 GENETIC DRIFT Refers to changes in allele frequencies of a gene pool due to chance. It is more obvious in small populations.

16 Bottleneck Effect – caused by a severe reduction in population (possibly a Natural disaster), reduces overall diversity.

17 Cheetahs have very little diversity in their gene pool due to bottleneck

18 FOUNDER EFFECT The 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

19 Five in Five, Five Words or Less
1. Gene Pool 2.  Microevolution 3.  Gene Flow 4. Phenotype 5. Genetic Drift

20 MACROEVOLUTION Evolutionary change at or above the species level
Speciation – the splitting of one species into two or more species

21 What is a Species? A group of actually or potentially interbreeding populations (isolated from other groups)

22 Hybrids occur when members of different species produce offspring...
Lion + Tiger =  Liger Tiger + Lion =  Tigon

23 Horse + Donkey = Mule Zebra + Donkey = Zonkey

24 SPECIATION Flycatcher species Empidonax minimus Empidonax virescens
Empidonax tralli What stops these species from mating with each other? (their DNA allows them to)

25 What would happen if two of these birds did mate?
Figure 18.10c Each 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?

26 MODES OF SPECIATION 1. Allopatric Speciation
Populations separated geographically b. Variations accumulate Aberts squirrel (south rim) Kaibab squirrel (north rim)

27 2. SYMPATRIC SPECIATION Sympatric speciation would occur when members of a single population develop a difference without geographic isolation. Ex. Apple maggot fly Hawthorn 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.

28 Allopatric vs Sympatric

A single ancestral species becomes several different species


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