Chapter 16 Evolution of Populations pg. 393

16-1 Genes and Variation Darwin’s lack of knowledge about genetics left him with two big gaps. He had no idea how traits pass from generation to generation. He had no idea how variation appeared.

Connecting genetics to evolution In the 1930’s evolutionary biologists began to connect Mendel’s work on genetics with Darwin’s ideas about evolution. Genes became the new focus of experiments aimed at understanding evolutionary change. Today our knowledge about genetics allows us to test hypotheses about inherited variations and how natural selection works with this variation. We understand how evolution works better than Darwin ever could.

How Common is Genetic Variation? We know many genes have at least two forms or alleles (Tt, tt or TT). Some organisms have several alleles for a trait. Body size, coat color, flower color, etc. Some variation is “invisible” because it deals with physiological processes. Immune systems, disease, health, etc.

Variation and Gene Pools Genetic variation is studied in populations. A population is a group of individuals of the same species that interbreed. Because members of a population interbreed, they share a common group of genes called a gene pool. A gene pool consists of ALL GENES present in a population.

The relative frequency of an allele is the number of times that an allele occurs in a gene pool when compared with the others. Example: 36% of the mice are brown and 64% are black. The percentages have nothing to do with dominant or recessive alleles.

EVOLUTION In genetic terms, evolution is any change in the relative frequency of alleles in a population. Example: the mouse population now has an relative frequency of 55% brown and 45% black. The population changed, therefore it is evolving…

Fish Activity This activity is a simulation of how fish and other organisms evolve in nature. Each team of two will need 8 green pieces of paper 8 red pieces of paper 8 yellow pieces of paper 1 “gene pool” your table. Each color represents a gene for color. Count your papers and be sure you have 8 of each color for a total of h.pdf

For Each Color Allele Green (G)Dominate to all colors. Red Allele (R)Recessive to green Incompletely dominant to yellow Yellow Allele (Y)Recessive to green Incompletely dominant to red What color will we get when red and yellow Alleles combine? Remember that each paper represents an allele NOT A FISH!

Directions Fill out the table at the top of your worksheet and answer questions 1-3. Green (G)Dominate to all colors. Red Allele (R)Recessive to green Incompletely dominant to yellow Yellow Allele (Y)Recessive to green Incompletely dominant to red

Generation 1 First put all of your alleles into the cup. What does this cup represent? Gene Pool! Make the first generation of your fish by randomly pulling pairs of alleles out of the cup without looking. You are representing the area of the water where the sperm fertilizes the egg. Record your genotypes and phenotypes in Table A.

Generation 1 Count the number of each color of fish offspring you hatched and record the numbers in Table B.

The Environment The stream in which the fish live is very green and lush with vegetation and algae. Green fish are well camouflaged. Red and orange fish do OK. Predators can easily spot the yellow fish. If you have any yellow fish, set them aside. These genes have now left the gene pool! Are there still yellow alleles in your population? Why?

Generation 2 Put all of the alleles from the living fish back into the gene pool (NOT the yellow ones that you just removed, the fish are dead, they can not breed!). Draw your second generation of fish from the cup and record your data in Table A. Total the fish of each color and record this data in Table B. Again, set aside your yellow fish that died due to predation.

Generation 3 Return all of your living fish alleles back to the cup. What’s happening to the alleles in your population? Draw a third generation from the cup and record your data in table A and B. Remove the yellow fish from the population and return the survivors back to the cup. STOP HERE! Answer the section 2 questions on your worksheet.

Generation 4 Put the alleles of the survivors back into the cup and draw your 4 th generation of fish. Record the data in Tables A and B. STOP! An environmental disaster has occurred! Factory waste has been released into your pond and is quickly killing off the algae. The remaining rocks and sand are good camouflage for the red, yellow and orange fish but the green fish are being killed off by predators.

Now… Remove all of your green fish from the population and record the SURVIVING offspring (all but the green) into the last row of table B (4 th generation survivors row).

Class Totals for 4th Generation Green FishRed (RR)Orange (RY)Yellow (YY) Now answer the question in section 3 of your worksheet.

Discussion Wild fish populations often have more genetic diversity than farm raised fish. How might less genetic diversity affect a fish populations ability to adapt to environmental disasters such as the pollution disaster in this simulation? If certain fish have lived in a stream for MANY generations, what might happen if their fertilized eggs were used to “restock” a different stream that no longer has fish? Give me an example in the real world of a population who’s lowered genetic diversity is impacting their ability to survive. Why do real populations change much slower than in this game?

Floridia Panther Historically occurring throughout the southeastern U.S., today the remaining approximately 100 panthers are found in south Florida and restricted to less than five percent of their historic range. The Florida panther was federally listed as an endangered species in 1967 and ultimately under the Endangered Species Act of 1973.

Sources of Genetic Variation The two main sources of genetic variation are mutations and genetic shuffling that results from sexual reproduction. Most heritable differences are due to the gene shuffling that happens during the formation of gametes, not due to mutations. Our 46 chromosomes can produce 8.4 million different combinations of genes. –Sex produces many different phenotypes but it does not change the relative frequency in a population.

Sex is like a deck of cards… Each card represents an allele found in a population. When gametes (sex cells) are made it’s like shuffling the deck. Shuffling leads to different hands but the number of cards remains the same.

Section 16-2 Evolution as Genetic Change In genetic terms, Evolutionary fitness is the ability of an organism to successfully pass its genes to the next generation.. Evolutionary adaptation is any genetically controlled trait that increases an organisms ability to pass on its genes.

Natural Selection Natural Selection affects which individuals survive and reproduce, or die without reproducing. Individuals that die do not contribute their alleles to the populations gene pool. Yellow fish and green fish. Individuals that reproduce contribute their alleles to their population and over time may increase in frequency.

EVOLUTION Any change over time in the relative frequency of alleles (traits) in a population. So it is populations, NOT individuals that evolve.

Genetic Drift Natural selection is NOT the only thing that causes evolutionary change. Genetic Drift is when an allele becomes more or less common by random chance.

Worm Simulation Genetic Drift on/act/drift/manual.html You will need 5 colored pencils for your table A die A worm worksheet

More on genetic drift… In small populations, certain individuals could have more offspring than others, by chance. Over time this could cause an allele to become more common in a population.

Colonizing new habitats Genetic drift can occur when a small group of individuals colonize a new habitat. The change in relative frequencies of the population in the new habitat is NOT due to natural selection, but due to chance or genetic drift.

Case in point Eastern Pennsylvania is home to beautiful farmlands and countryside, but it's also a gold mine of information for geneticists, who have studied the region's Amish culture for decades.

The Founder Effect Because of their closed population stemming from a small number of German immigrants -- about 200 individuals -- the Amish carry unusual concentrations of gene mutations that cause a number of otherwise rare inherited disorders. Let’s take a closer look… html

Ellis-van Creveld Syndrome In the general population, the frequency is 1 case per 60,000 live births. Among persons from the Old Order Amish, the incidence is estimated at 5 cases per 1000 live births. The frequency of carriers in this population may be as high as 13%.

The Founder Effect When allele frequencies change as a result of the immigration (moving in) of a small subgroup of a population, it is known as the founder effect.

Let’s try this out! Get into the following groups. Everyone with light colored eyes (blue or green), go over to the laptop cart. Everyone with dark eyes go to the other side of the room.

Sooo……… Can you name three things that will cause a population to evolve over time?

When will evolution NOT occur? What are some things that would prevent evolution from happening?

Hardy-Weinberg Principle Alleles in a population will stay the same unless something causes them to change. (HW Principle) Genetic Equilibrium is when allele frequencies remain the same (no evolution). If allele frequencies stay the same, populations will NOT evolve!

So, for no evolution to happen we’ll need the following… 1.There must be random mating. 2.The population must be very large. 3. There can be no movement of organisms in or out of the population. 4. No mutations. 5. No natural selection.

Review of Classification Take a copy of the “Classification of Living Things” worksheet. We are going to use BrainPop to review scientific classification of organisms before we move on. Classification of mammals mals/classification/index.shtml mals/classification/index.shtml

Evolutionary Relationships Organisms are classified by their similarities. Now that we know more about evolution and genetics, we use those details to classify life based on their common ancestors. Let’s learn how scientists use current organisms and fossils to determine evolutionary relationships. Go to ons/tours/Trex/index.html ons/tours/Trex/index.html Or type in What Did T-Rex Taste Like The information you learn from this web-site will be used in our next assignment.

Section 16-3 The Process of Speciation How do the changes in allele frequencies in a population form new species????? Species: a group of organisms that can breed with one another and produce fertile offspring. Speciation is the formation of a new species.

Speciation In order for new species to arise, the gene pool of a population must be separated. Reproductive isolation happens when a population can no longer interbreed and produce offspring. This creates separate gene pools.

Geographic Isolation

When two populations become separated by a river, mountain or body of water it is called geographic isolation.

Let’s watch how this happens… emos/Chapter_4/Chapter_04/Present/ animations/23_2_2_1.html

Behavioral Isolation Behavioral Isolation occurs when two populations are capable of interbreeding but have differences in mating or courtship rituals. Example: Western Meadowlark mating calls adowlark/sounds and Eastern Meadowlark adowlark/sounds mating calls are different. adowlark/sounds adowlark/sounds

Temporal Isolation Temporal Isolation occurs when reproduction happens at different times. Example: When plants release pollen on different days and can not pollinate one another.

Back to the finches! Recall that Darwin found many birds on the Galapagos that differed greatly in their sizes, beaks, and in their feeding habits. Once Darwin realized that they were all finches, he hypothesized that they had all come from a common ancestor. He proposed that natural selection shaped the beaks of the different bird populations as they adapted to eat different foods. Good hypothesis, but how do you test it?

Testing the hypothesis… Darwin had two testable assumptions. 1. In order for beak size and shape to evolve there must be enough variation in those traits. 2. Differences in beak size must produce differences in fitness.

Peter & Rosemary Grant The Grants tested these hypotheses with the medium ground finch, on an island large enough to support many finches, but small enough to allow them to catch and identify nearly every bird under study.

Did enough variation exist? First, identify and measure as many birds as possible on the island. Record the birds that live and die, and which have breed or not. Take measurements of their physical features. Data indicated that there is great variation among the Galapagos finches!

The Grants most interesting discovery… Individual birds with different sized beaks had different chances of survival during a drought. Chapter 16, Natural Selection video y/discoverbio3/core/content/index/animat ions.asp

Evidence of the process of evolution The Grants research provided evidence of the process of evolution by natural selection. Found that natural selection takes place frequently. Sometimes it happens very rapidly.

Speciation in Darwin’s Finches Founders, from species A, arrive on the island from South America. Some of the birds from species A end up on a nearby island becoming isolated from the others. Changes in the gene pools on each island, due to different availability of foods allows natural selection to favor certain individuals.