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Hardy-Weinberg Activity Hardy-Weinberg Activity Hardy-Weinberg Activity Microevolution in the Eastern Squirrel Microevolution in the Eastern GrayGray Squirrel BACKGROUND Microevolution Squirrel Microevolutioninofthe theEastern Eastern Gray Gray Squirrel Gray Variant Gray Variant Gray Variant (wild type) (wild (wildtype) type) Gray Variant (wild type) As we have seen with these squirrels, some alleles may be more common than others in Black Variant a gene pool. For example, let’s suppose that if we counted all the squirrels around the Variant Black (mutant)Black Variant ABRHS campus, we found the population to be 20% black and 80% gray. The gene(mutant) (mutant) Black Variant frequency in a population for the Hardy-Weinberg Equilibrium is written as: (mutant) pp : 2pq : qq or p2 + 2pq + q2 = 1 Key Genotypes: Black phenotype homo dom. = hetero. = Gray phenotype homo rec. = where p = the frequency of the dominant allele (black) , and q = the frequency of the Squirrels competing forItlimited theirofenvironment recessive allele (gray). followsresources that p + q =in100% all the genes in the gene pool. Squirrels competing for limited resources in their environment Squirrels competing for limited resources in their environment For this population,for qq =limited .80. Therefore, the in square of .80 = .89, or 89% of the genes Squirrels competing resources theirroot environment Evolution, on a genetic level, is a in change ingene the pool. frequency allelesofinthe a dominant population Eastern this small So, the of frequency alleleover musttime. be 11%The of the total Gray Squirrel INTRODUCTION for furincolor. In other squirrels which are homozygous for the dominant (Sciurus carolinensis) demonstratesgenes evolution action. Thiswords, familiar species, commonly seen pillaging bird feeders and gene make uphas about 1% (.11 x .11) of the total WhileFlorida 19% (2pq 2 x .11 xCanada and into INTRODUCTION scampering about trees in your neighborhood, a geographical range thatpopulation. extends from up=through are the heterozygotes, and 80% are the homozygous recessive What to domany, porcupines, flying squirrels, mice, and naked mole ratsfrom all individuals. have in gray-furred parents. Such the Midwest. Surprising the.89) “gray” squirrel hasbeavers, a black variant that can be born normal INTRODUCTION They belongmore toflying one ofsquirrels, the most andmice, successful of all m ammals – the offspring contain a common? mutation that causes pigment to bediverse concentrated in and theirnaked hairs, giving these squirrels What do porcupines, beavers, mole rats all have in a black MATERIALS (per group) appearance. Offspring born from such mutants are likely to inherit this trait since it is a dominant allele. rodents. In fact, forty percent of all species of mammals are rodents. Living worldwide Theyflying belongsquirrels, to one ofbeavers, the mostmice, diverse successful allhave m ammals – the Whatcommon? do porcupines, and and naked mole ratsofall in in rodents. extremely varied habitats, from tropical sea usually shores tovery icy rare, mountain ranges, rodents In this activity you will investigate a mystery: black squirrels are but are common in–concentrated In fact, forty percent ofmost all species of are Living worldwide populations in common? They belong to one of the diverse andmammals successful ofrodents. all m ammals the Beaker of grayish beans demonstrate adaptability ofespecially life. But in how did these chisel-toothed creatures adapt to some parks throughout Easternthe America, colder city parks around the Great Lakes of America and Canada. Beaker black rodents. In fact,North forty percent ofbeans allfrom species of mammals areto rodents. Living worldwide in extremely varied habitats, tropical sea shores icythis mountain ranges, rodents What biological process or mechanism might account for this? Can we model how might work? such extremes? 1 plastic bag in extremely varied from of tropical sea shores to these icy mountain ranges,creatures rodents adapt to demonstrate thehabitats, adaptability life. But how did chisel-toothed 3 empty beakers demonstrate the adaptability ofislife. But how did these chisel-toothed creatures adapt to MATERIALS (per group) such extremes? Masking tape Evolution, on a genetic level, a change in the frequency of alleles in a population over 100 beans (50 each of 2 colors) such extremes? time. The Eastern Gray Squirrel (Sciurus carolinensis) demonstrates evolution in action. 1 plastic bag Evolution, on PaROCEDURE genetic level,seen is apillaging change in thefeeders frequency of alleles in a population over This familiar species, commonly bird and scampering about trees 3 emptyEvolution, cupstime. on genetic level, a change in the frequency of alleles in a population over Thea Eastern Gray is Squirrel (Sciurus carolinensis) demonstrates evolution in action. in neighborhoods 1.around Acton, has a geographical range that extends from Florida up Get into a group of 4-5 people and get the materials listed above (6 groups in a class). Thefamiliar Easternand Gray Squirrel (Sciurus carolinensis) demonstrates This species, commonly seen pillaging bird feeders andevolution scampering about trees PROCEDURE time. through Canada into the Midwest. Surprising to many, the “gray” squirrel hasinaaction. This familiar species, commonly seen pillaging bird feeders and scampering about trees 1. Obtain the materials listed above. black variant that 2.can beblack bornbeans fromrepresent normal gray-furred parents. Such contain a theup in neighborhoods around Acton, has athe geographical range that extends from Florida The allele for black fur, and the offspring grayish beans represent in beans neighborhoods around has geographical range that extends from Florida up mutation that causes more melanin toafur, be concentrated in their hairs, giving these squirrels allele forActon, gray fur. The plastic bag the environment in eastern North America through Canada and into Midwest. Surprising to many, the “gray” squirrel has 2. The black represent the allele forthe black and therepresents grayish beans represent the allele for graya fur. through Canada and into thebeMidwest. Surprising toAmerica many, the “gray” squirrel has a contain abag black appearance. Offspring bornin from suchNorth mutants are likely to inherent trait black variant that can born from normal gray-furred parents. Suchthis offspring 3. The plastic represents the environment eastern where the squirrels randomly mate.a black variant that can be born from normal gray-furred parents. Such offspring contain a since it is a dominant allele. mutation thatFF” causes more melanin todominant be concentrated inLabel theirdominant giving squirrels 4. Label one cup “Black Fur, for the homozygous ahairs, second cup these “Black Ff” for the 3. more Label one beakerto “Black Fur, FF” forgenotype. the genotype. LabelFur, a mutation thatappearance. causes melanin be concentrated inhomozygous their hairs, giving these squirrels black Offspring born from such mutants are likely to inherent this trait heterozygousa genotype. Label the third cup “Gray Fur, ff” for those squirrels with the homozygous recessive genotype. second beaker “Black Fur, Ff” for the heterozygous condition. Label the third beaker URPOSE aPblack appearance. Offspring from such mutants are likely to inherent this trait since it is a dominant (See below): “Gray Fur,allele. ff”born for those squirrels with the homozygous recessive genotype. (See below): where the squirrels randomly mate. since it is a dominant allele. In this activity you will investigate a mystery: black squirrels, usually very rare, are Beakers: PURPOSEin concentrated Black in som e parks Black common populations throughout Eastern Gray North America, PURPOSE Fur FF Fur Ff Fur ff especially in colder city parks around the Great Lakes of America and Canada. What In this activity you will investigate a mystery: blackCan squirrels, usually verymight rare, are process or mechanism might account for this? we model howrare, this In biological this activity you will investigate a mystery: black squirrels, usually very are America, common in concentrated populations in som e parks throughout Eastern North work? in concentrated populations in som e parks throughout Eastern North America, common 5. Each group will start within50 blackcity andparks 50 gray beans. the 100 beans (representing alleles) into the plastic bag and especially colder around thePut Great Lakes of America and Canada. What in colder city parks around the Great Lakes of America and Canada. What shake it especially up (represents a mixing of alleles via reproduction between squirrels.) biological process or mechanism might account for this? Can we model how this might biological processatoramechanism might for this?and Can we model how this might 6. Select two beans (alleles) time from the bag account without looking, record the results on the data form next to work? work? "Generation 1." For instance, if you draw one black and one gray bean, place a mark in the chart under "Number of Ff individuals." Continue drawing pairs of beans and recording the results in your chart until all beans have been selected and sorted. Place the "squirrels" into the appropriate cup: FF, Ff, or ff. 7. Count the F alleles (beans) in each container. Do the same for the f alleles. Total the number of F alleles and f alleles for the first generation and record this number in the column labeled "Total Number of Alleles.". 8. Determine the allele frequency of F and f for each generation and record them in the chart in the columns labeled "Allele Frequency F" and “Allele Frequency f." To find the gene frequency of F, divide the number of F by the total, and to find the gene frequency of f, divide the number of f by the total. Express results in decimal form. The sum of the frequency of F and f should equal one for each generation. 9. The FF and Ff squirrels are born with shiny black fur. Squirrels with black fur living in a wooded environment stand out against the dull gray/brown background more than their gray-furred relatives (see photo above for an example). This is especially true in the colder months once deciduous trees have dropped their leaves, creating a landscape full of grayish trees and a forest floor covered by brown, dried leaves. The shiny, black-coated squirrels easily stand out in this environment, especially in large forest tracts where red-tailed hawks abound. These keen-eyed raptors spot the conspicuous black squirrels and swoop down upon them often before they can escape. Therefore, the black variants are less likely to reach reproductive age and pass on their black fur alleles. Place half the beans from the FF and Ff containers aside before beginning the next round. 10. Repeat steps 6-9 to obtain generations 2 and 3. DATA TABLE Generation # of FF individuals # of Ff individuals # of ff individuals Number of F alleles Number of f alleles Total # of alleles Frequency of F allele Frequency of f allele 1 2 3 ANALYSIS 1. Graph how squirrel color allele frequencies changed over the three generations of this simulation. Then contribute your data to the class data. 2. How does your group’s results compare with the class data? If different, what caused them to be different? 3. How are the results of this simulation an example of evolution? 4. As you have seen in this activity, gray squirrels predominate due to the fact that they are camouflaged better than their black-coated relatives. However, biologists have measured that black squirrels have 18% lower heat loss in temperatures below -10 degrees Celsius and therefore shiver less (by 11%) compared to the gray variety. How does this study answer why concentrated populations of black gray squirrels are found commonly in some northern city parks?
