Chapter 16 Evolution of Populations w 16 1

Chapter 16: Evolution of Populations w 16. 1 Genes and Variation w 16. 2 Evolution as Genetic Change w 16. 3 The Process of Speciation

Population Genetics w Evolutionary thought today is tightly linked to genetics. w Remember, populations, not individuals evolve. w All the alleles in a pop. added together are called the gene pool .

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Population Genetics w The frequency that any one allele is seen in the population is called the allele frequency (relative frequency). Is the frequency of the dominant Huntington’s allele high? n Is the frequency of the dominant allele causing 6 fingers high? n

Population Genetics w If the frequency of the alleles doesn’t change over time, the population is at genetic equilibrium . w Hardy-Weinberg Principle n see page 401

Population Genetics w When alleles are brought in and out of a population due to migration of individuals, it is called gene flow.

Population Genetics w When isolated chance events can alter gene frequencies in a population (therefore disrupting gene equilibrium) you have what is called genetic drift. n n n Common in small isolated populations such as the Amish of Lancaster, PA Darwin’s finches (perhaps) founder effect: change as a result of migration

Population Genetics w Sources of Genetic Variation: n n Mutations Gene Shuffling Single gene trait Polygenic trait

Population Genetics w Types of selection: n When natural selection of a trait favors the average individuals in the pop. it is called stabilizing selection.

Population Genetics w Types of selection: When natural selection favors both extreme phenotypes of a trait in a pop. , it is called disruptive selection. n

Population Genetics Types of selection: When natural selection favors one extreme phenotype of a trait, it is called directional selection. n

Population Genetics w Type of Selection? ? n n n Grey mice are preyed upon but black and white mice are left alone? Disruptive The longer a giraffe’s neck gets the more food is available, while short necked giraffes die of starvation before they can reproduce? Directional A slow gazelle is easily caught by a cheetah, but one too fast breaks its legs easily and is eaten by hyenas? ? Stabilizng

Population Genetics w Artificial Selection: Selection for traits that are determined and monitored by man. n Ex. Breeding animals such as dogs or cats. w Sexual Selection: Selection by one gender for another gender. n Ex. Peacock feathers, body hair disappearance in humans, walrus tusks.

Speciation w Speciation is when a new species is formed. This means that the individuals in the new species can no longer produce successful offspring with the population from which they came.

Speciation w Geographic Isolation cause speciation over long periods of time. n n The seperated organisms are adapting to different environments and responding differently. Eventually if a mating is attempted, they can no longer produce successful offspring with one another.

Speciation w Reproductive Isolation is when a population can no longer successfully interbreed with its parent population (the pop. it came from). n Reproduction if attempted will fail. Ex. One group breeds in the fall, one in the spring and over time the populations become new species incapable of interbreeding. n Mating Calls n Courtship rituals differ n

Speciation w Temporal Isolation: n n Two or more species reproduce at different times Example: orchid in the rainforest

Speciation w Changes in chromosome number can cause speciation. w Some cases of polyploidy (more common in plants) produce individuals that can only mate with other polyploids in a pop.

17. 4 Speciation w Can occur rapidly Punctuated Equilibrium n Gould n w Can occur very slowly Gradualism n Darwin n see page 439 n

17. 4 Patterns of Evolution w Adaptive Radiation: When an ancestral species evolves into several different species, each filling a specific niche. Darwin’s finches n Hawaiian Honeycreepers (p. 406 &436). n

17. 4 Patterns of Evolution w Divergent Evolution: Species that once were similar or closely related become very different. n n New Species are very different from each other. Ex. Adaptive Radiation

17. 4 Patterns of Evolution w Convergent Evolution: Unrelated species that live in similar environments evolve the same adaptations in order to survive. n n Ex. Tasmanian Wolf and North American Wolf. P. 437

Patterns of Evolution w Coevolution: the process by which two species evolve in response to changes in each other over time. n n Example: flowering plants and their pollinator Page 437 http: //biology. clc. uc. edu/courses/bio 303/coe volution. htm

17. 4 Note w Common genetic occurrences we have studied such as polyploidy, crossing over, and point mutations can provide the genetic basis for evolution. Although these genetic changes are not evolution themselves, they can begin the long process of evolution by affecting one individual in a population in a positive way. But only if the trait is passed on, and on…