2/1/ 2011 Warm up  Summary of Darwin’s Theory 1._______________________differ. 2. competition for _______________ 3. best _________to environment survive. 4. Species alive today are descended with _________________

Ch. 16: Outline  16-1: Genes and Variation  How common is Genetic Variation?  Variation and Gene Pools  Sources of Genetic Variation  Single-Gene and Polygenic Traits

16-1: Genes and Variation  When Darwin developed his theory of evolution, he stated that organisms pass on their traits to their offspring (inherited variation).

 Darwin did all of his work on natural selection and evolution, but he did not even know how heredity worked! Scientists had not discovered genes!!!!

 Biologists connected the work of Gregor Mendel to Darwin in the 1930’s. Our inherited traits are determined by our genes. Genes pass on our inherited traits to the next generation.  It is the differences in the genetic makeup of individuals within the same species that leads to natural selection.  These differences are called genetic (inherited) variation.

Variation and Gene Pools  Scientists study genetic variations by studying populations of species.  Population: A group of species in a specific area  Gene pool: All genes (including different alleles) that are in population.

 Relative frequency: The number of times that an allele for a specific gene occurs in a gene pool, compared to the number of times other alleles for the same gene occur.  In genetic terms, evolution is any change in the relative frequency of alleles in a population.

What is genetic (inherited) variation?  Differences that exist in the genetic makeup of individuals within the same species

Sources of Genetic Variation  How does genetic variation occur? The two main sources of genetic variation are mutation and gene shuffling.  1) Mutation: any change in a sequence of DNA  Mutations are caused by a mistake in replication, radiation, or chemicals in the environment  Some mutations are harmless, but others can affect an organism’s fitness:  Fitness: The ability to survive and reproduce

Sources of Genetic variation  2) Gene shuffling:  Genes on chromosomes are shuffled during MEIOSIS when gametes (sex cells) are formed!  Review of Meiosis  Segregation  Independent Assortment  Crossing-over  Thus, sexual reproduction is a major source of genetic variation

 Which is a greater source of genetic (inherited) variation – mutations or sexual reproduction? Justify your answer.  Sexual Reproduction

Single-Gene and Polygenic Traits  Some inherited traits are controlled by one (single) gene or many genes (polygenic)  The number of phenotypes produced for a given trait depends on how many genes control the trait.

Single-Gene and Polygenic Traits  Single-gene traits are any trait that is controlled by one gene. This trait will have only two alleles  Widow’s Peak (dominant) is a single- gene trait  Only two phenotypes are possible

 If Widow’s Peak is represented by the letter W and a normal hair line represented by w, what are the possible hairline genotypes in the population ?  ww (normal hair line)  Ww (Widow’s Peak, heterozygous)  WW (Widow’s Peak, homozygous)

Single-Gene and Polygenic Traits  Polygenic Traits: are traits that are controlled by two or more genes.  These traits have more than two alleles  This means that there are many possible phenotypes and genotypes.  Skin color and height are examples of polygenic traits

Ch. 16: Outline  16-2: Evolution of Genetic Change  Genetic Drift  16-3: The Process of Speciation  Speciation

16-2 Evolution as Genetic Change  Evolution causes changes over time in the relative frequencies of alleles (inherited traits) in a population. Thus, populations evolve over time.

Genetic Drift  In small populations, chance alone can cause a change in the allele frequency in a population. This is called genetic drift.  Example of Genetic Drift:  Founder effect: When allele frequencies change because of the migration of a small number of individuals out of a population.

Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift

Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift

Sample of Original Population Founding Population A Founding Population B Descendants Genetic Drift

16-3 The Process of Speciation  How do the changes in allele frequencies (evolution) lead to a new species?  Speciation: the formation of a new species.  Speciation occurs when two populations become reproductively isolated from each other

Isolating Mechanisms  There are three ways for reproductive isolation to occur:  Behavioral Isolation  Geographic Isolation  Temporal Isolation

Behavioral isolation: Two populations have differences in courtship rituals or other reproductive strategies that involve behavior. Species live in the same geographical area.

Isolating Mechanisms Geographic isolation: Two populations are separated by geographic barriers such as rivers and mountains. (Squirrels) A. harrisi A. leucurus

 Geographical isolation caused the speciation of the finches in the Galapagos Islands

Isolating Mechanisms Temporal isolation: Reproduction occurs at different times of the year. Species live in the same geographical area. The American Toad (Bufo americanus) mates in early summer The Bufo Fowelri mates in late summer

results from which include produced by which result in Reproductive Isolation Isolating mechanisms Behavioral isolationTemporal isolation Geographic isolation Behavioral differencesDifferent mating times Physical separation Independently evolving populations Formation of new species

Chapter 17  17-4: Patterns of Evolution  Extinction  Gradualisms vs. Puntuated Equilibrium

 The fossil record provides evidence about the history of the Earth.  The fossil record indicates that species have change over time (evolution).  The fossil record shows that some species are no longer alive

 Certain fossils can only be found in older rocks, for example (and are not found in any recent rocks). When a species is no longer living, it is extinct.  Extinct: a species that has died out.

 Reasons for extinction of species include  Changes in climate  Disruption of ecosystems  Inability to compete for resources

Gradualisms vs. Punctuated Equilibrium  Modern scientists disagree with Darwin about the speed of evolution.  Darwin believed that evolution is a slow, gradual process. This process is termed gradualism.

Gradualisms vs. Punctuated Equilibrium  The fossil record indicates that this is true for some species.  But other species are produced by short periods of rapid change (also supported in the fossil record).  Puntuated equilibrium: is the pattern of long, stable periods of change that is interrupted by brief periods of more rapid change

Gradualism model. Species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations. Time Punctuated equilibrium model. A new species changes most as it buds from a parent species and then changes little for the rest of its existence.

Gradualisms vs. Punctuated Equilibrium  What causes punctuated equilibrium?  Migration  Isolation  Mass Extinctions