Exploring Human Traits Genetic Variation

PRISM UHH GK-12Genetic VariationConceptsGenes are passed on fromone generation to the nextand this is the concept ofheredity. Genes code forwhat an organism willlook like and are carriedby chromosomes.Chromosomes, whichoccur in nearly identicalpairs in the nucleus ofevery cell, are responsiblefor passing on hereditaryinformation. Dependingon which alleles anorganism has willdetermine how theorganism will look andbehave.Standards addressed7.5.2, 7.5.3, 7.5.6Duration1-2 60 minute classperiodsVocabularyHappy-face SpiderHomologousPhenotypeGenotypePunnet e MaterialPRISMHappy-Face Spider PropagationSummaryStudents will act as captive breeders in order to simulate how genes are passed onfrom one generation to the next. They will also observe how small differencesaccumulate over time to produce descendants that look very different from theirancestors. Students will use the Happy-face spiders (Theridion grallator), a spiderthat is endemic to the Hawaiian Islands and exhibits genetic variation. Spiders onthe island of Maui follow basic Mendelian genetic patterns, so they will be usefulorganisms for this lesson. This simulation will help students determine howgenetic information is transferred during breeding, and what the resultingphenotype (how they look) will be. They will decide which traits are mostimportant to breed in order for better survival for the spiders. Students will also beintroduced to Punnet squares, which will be used to predict the proportion ofoffspring with each trait.Objectives Students will learn about a species that is endemic to Hawaii Students will simulate how genes are passed from one generation to thenext. Students will act as captive breeders and choose which traits will help thesurvival of the spiders. Students will use Punnet squares to predict the proportion or frequency ofwhich genes will be passed on.MaterialsPictures of Happy-face spiders that show variation in color.Pink and Blue Card Stock-each group of 2 students should have a total of 12 pinkcards and 12 blue cards. (Size of playing cards). Need one set for use in explainingconcept to students.Clear transparency to go over Punnet squaresPaper for student Punnet squares.Hand-out of Happy-face Spider for students to color using their color choice.BackgroundHappy-face spiders are found in the rainforests of the Big Island, Oahu, Maui andMolokai. They are usually found on the underside of leaves. Happy-face spidershave a pattern on their body that resembles a smiley face. Every spider has aunique pattern and the body color differs from island to island. Some of thespiders lack the pattern of the smiley face alltogether. These different morphs(forms) are caused by the different gene versions carried by the spiders. Thecombination of alleles on the homologous chromosomes (similar, pairedchromosomes) which determine a specific trait or characteristic is the organism’sgenotype. The way the information is expressed and how the spider looks isconsidered its phenotype. Genotypes and phenotypes of an organism can bedetermined with the use of a Punnet square which estimate the probability(likelihood) of genetic combinations being passed on to potential offspring. APunnet square is created by crossing either homozygous (two identical alleles)alleles, heterozygous alleles (two different alleles) or a combination of both on agrid.Researchers believe that the variation of color and pattern in Happy-face Spiders isa possible type of camouflage against birds, their only significant natural predator.

In order for these spiders to escape predators they must be able to blend into their natural environment. If thestudent is to be the captive breeder they must decide what would be the best color for the spider to survive in thewild.Teacher Prep for Activity Review background reading for Genetic Variation Xerox Happy-face Spider Drawing page. Cut out cards for the students: a group of two students will have one set of 12 blue cards and one set of12 pink cards. Be sure to make a set to use as an example when explaining the activity to the students.Except for the set to be used by the teacher, the other sets of cards should remain blank since the studentswill be writing in the color traits that they will be using. These cards could be laminated and used yearafter year, if dry erase markers that could be cleaned off were used. Have a clear transparency handy to go over the Punnet squares after they have finished the “card game”.Procedure1). Split students into groups of two and pass out drawing sheet. One student will act as the MOTHER passingon traits to its offspring and they will receive 12 blank PINK cards. The other student will act as the FATHERpassing on traits to its offspring and they will receive 12 blank BLUE cards.2). Before the students start working on the cards, have them draw a Punnet square (more information aboutPunnet squares can be found on pg. 257 in the FOSS readings at the back of the lessons) to determine what theprobability of allele combinations will be (this can be done on the back of the drawing page). The students willhave to choose if the dominant parent will be either heterozygous (Ww) or homozygous (WW or ww). Theyshould work together on creating the Punnet square.3). Ask the students to determine which color they would like to represent. Remember: this color should bebeneficial for their survival in the wild. If a student chooses fluorescent pink, they will have to explain how thiscolor would allow the spider to be camouflaged in the rainforest. The mother and the father should be 2 differentcolors. For example: Mom White, Dad Yellow.4). Next, ask the students to choose which color is going to be dominant and which is going to be recessive andassign the correct genotype to the respective trait. Remember: the letter designated must be the same for eachcolor but must be represented by either a capital letter or lower cased letter. For example, if mom is consideredto be dominant for White, then her genotype would be WW or Ww (students can choose, WW x ww will onlyhave Ww offspring which will all be the dominant color, white in this case. If more variation is wanted inoffspring, have the dominant parent be Ww, since Ww x ww will have 50% white and 50% yellow) andeventhough dad is yellow, his recessive genotype would be ww.5). Ask the students to take a card and write one allele type per card. For example, for mom, each pink cardshould have a W written on half (6) the cards and the other half (6) will have a lower-cased w written on them, ifyou make mom heterozygous. If mom is homozygous then all her cards will have W on each one. For the bluecards, for dad, each card should have a lower-cased w written on it, since the gene is recessive he will only bepassing the recessive gene on.6). Now have the student with the pink cards shuffle their cards and the student with the blue cards shuffle theircards as well. Then have the students lay all the pink cards out next to each other and below that row of cards,lay out all the blue cards. Be sure the cards are lined up above and below each other to show how the differentgenes line up.7). Once the cards are laid out, have the students look at the frequency of the combinations of traits. Ask thestudents to compare the probabilities of the allele combinations from their Punnet squares (on the back of theirdrawing page) to the frequencies created from the cards they made.

AssessmentsJournal writing and coloring picture of spider to accompany writing or defense of color choice.Class presentation on spider color brary/article/ 0/happyface 02Google images-http://images.google.com/Foss-Populations and Ecosystems

Name:Color the body of the Happy-Face Spider the color that was chosen to breed the spider for survival in the wild.Use the extra space behind the spider to draw the habitat where this spider can be found.UHH PRISMDrawing by: Bobby HsuBobby Hsu

Look under a leaf and find a smiling surprise. But look out, because I like to catch my prey ina silken trap.WHO AM I?Color the numbered spaces to find me.1 red2 black3 -.-.afl InR.S - h L . C b o 0 3Unscramble the letters to find out.1.P Y P A H E F A CD E P I R S

Coloring and Activity Book

.-.- 3565 Harding Avenue Honolulu, Hawai'i 96816-b-.--.

http://nature.berkeley.edu/ gillespi/research.htm

http://nature.berkeley.edu/ gillespi/research.htm

http://nature.berkeley.edu/ gillespi/research.htm

http://nature.berkeley.edu/ gillespi/research.htm

http://nature.berkeley.edu/ gillespi/research.htm

In Genetic Variation students learn the basic genetic mechanisms that determine the traits express1individuIn.SCIENCThe individuals in evt?rypopu:lation vairy from c n eanother in their traits.Heredity is tlle passin g of info]nation f rom one generation to the next. ,.Chromosomes are structures that contaln hereditary information and transfer it to the next generation;they occur in nearly icientical F)airsin tEte nucleu.s of every cell.Gentes are thc? basic urlits of he]redity c a:ried by c:hromosabmes. Genes code for features of or . .- . . .A l l,lesaare vanations ot genes that d e t e r m e tralts in orgarusms; the two alleles on pairedchrolmosomes constik t ae gene.Alleles can bc2 dominamt or recessive. Dominant alleles exhibit the!ir effect if they arc2 present on onechromosome; recrsslve alleles exhibit their effect only when they are on both chromosomes.An organism's particular combination of paired alleles is its genotype; the itraits produced by thosealleles result in the organism's phenotype.A gene composed of two identical alleles (e.g. both dominant or both recessive) is homozygous; agene composed of two different alleles (i.e. one dominant and one recessive) is heterozygous. .CONDUCTING INVESTIGATIONSObserve vari ation in 1luman tr(aits and 1arkey traits.Use a simula tion to dt2termine the transfer of genetic information during breeding and the traits thatresult.Use Punnett squares to predict the proportion of offspring that will have certain traits.BUILDING EXPLANATIONSExplain how organisms Inherit features and traits from their parents.Describe how dominant and recessive alleles interact to produce traits in a population.

-,-;-,1SCIENTIFIC AND HISTORICAL BACKGROUNDI,.iIIn their ecoscenario studies, students wereintroduced to two dozen or so keyorganisms that interact in a particularecosystem. That's quite a few organismsto keep track of for middle schoolers, butin fact, the handful of species presented forstudy represents only a tiny fraction of theactual number of species living andinteracting in the most diverse and robustecosystems.Diversity raises questions. How can somany different populations live in thethesame ecosystem? And where diddifferent species come from in the firstplace?; In Investigation 8 students wereintroduced to important concepts that getat the first question. The simple answer isthat all organisms living in an ecosystemhave adaptations that let them get theresources they need to live and reproduce.Close analysis reveals that every specieshas a unique suite of adaptations. Thisensures that when resources are limited,every organism will use at least slightlydifferent resources, in a slightly differentway, at a slightly different time, in aslightly different place. In this wayorganisms keep out of each other's wayand avoid excessive competition forvaluable resources. In a sense an organismis defined by its adaptations; similarly itsrole in the ecosystem is defined by itsadaptations. Organisms that are notadapted to live in a particular ecosystemare not found there.Why there are so many different kinds oforganisms in an ecosystem is one of themonster questions in biology. Presumablylife started on Earth as one kind (orpossibly several) and over the last 3.5billion years diverged into hundreds ofmillions of different kinds, a small Fractionof which are living on the planet at thistime. What process could have producedso many kinds of organisms?Most biologists concur that the theory ofnatural selection provides the answer. Thetheory stands on several tenets.First, there is variation in a population oforganisms. The variation can be the resultof mutations and recombinations in thegenetic code, but these concepts will notbe pursued in this course. Variation in apopulation may be the result ofimmigration and emigration (gene flow)or the random change in the frequencies ofalleles (genetic drift). We will accept as afact of life that there is variation in themany features of individual organisms,and they stem from natural processes.These variations are traits.Second, environments are dynamic,continually presenting new and differentchallenges for the organisms living inthem. The environmental change could bethe introduction of a new organism betteradapted to compete for resources, achange in the climate, a disaster of somekind, or any number of subtler changes.An organism that was adapted before thechange in the environment may not beadapted to cope after the change.Ecologists call this changed condition a

selective pressure. The change in a veryreal way selects the organisms that willsucceed and those that will fail. There is,of course, no conscious decision to selectthis organism and eliminate that one.If the selective pressure is radical, a wholepopulation may succumb. If the pressureis slight or incremental, however, thepressure may be felt by only somemembers of a population. That is to say,some traits, such as thin fur, pale skin, orshort legs, might preclude an organismfrom acquiring resources or reproducing,so those traits will be selected against inthe population.Other members of the- population might continue to survive andreproduce, perpetuating their traits. Inthis way the appearance and/ or behaviorof a population as a whole can change,sometimes in a relatively short time.The third factor contributing to naturalselection and the evolution of new speciesis isolation. As long as the members of apopulation interact and breed, they willnot normally generate a new species. Thepopulation may change over time, but willnot become a new species. If one portionof a population is separated from theother, either physically (isolated bygeography) or behaviorally (exploitingdifferent food sources), creating twopopulations, new species may evolve.When a portion of a population emigratesor is transported to an island or newcontinent, the selective pressures in thetwo environments-the originatingenvironment and the new environmentmay favor different traits. After a periodof time, from decades to scores ofmillennia, the two populations may havediverged to such an extent that, even ifthey were reunited, they would continueto conduct their separate lives, unable tomate and reproduce.That's an oversimplified picture of theorigin of species, but in practice thescience of identifying the precise point inthis process when a new species hasarrived is daunting, and even a precisedefinition of what constitutes a species isillusive. We will not enter these deepwaters in this course.MECHANISMS FOR POPULATIONCHANGE:.The key to population change is variationamong the individuals in the population.In a population of sexually reproducingorganisms, each individual is unique andtherefore has ever-so-slightly differentneeds, behaviors, tolerances, andresponses to stimuli from theenvironment. When the environmentchanges, the makeup of the populationchanges in response.-What makes each individual unique?Genes. The genes that direct the assemblyof molecules into organisms are differentfor every individual.1,This discussionapplies to organismsthat reproducesexually. Organismsthat reproduce bysimple division,producing twogenetic clonedaughters, follow aslightly different pathto achievepopulation change.

The simple version of genetic transfer ofinformation goes like this. The story of lifeis recorded in huge molecules callednucleic acids. The specific nucleic acidthat handles the genetic code is DNA(deoxyribonucleic acid). The longfilaments of DNAare made ofmillions of sugarand phosphateunits bondedtogether, withorganic basessticking out tothe side.Picture a comb.The sugar /backbone sportslike tines.9The bases sticking out are keyto the structure of DNA. The four basesare adenine, thymine, guanine, andcytosine, usually represented by thesymbols A, T, G, and C. The bases canbond with one another, but only in specificbonding pairs. A and T can bond with oneanother, and C and G can bond, but Acannot bond with C or G, and so on. Basepairing is specific, and there are noexceptions.The bases on two sugar / phosphatestrands bond and form a double DNAstrand called a double helix. The result isa long ladder with the bonded basesforming the rungs.

A typical DNA molecule might be 5 cmlong. To fit in the nucleus of a cell, thehuge molecule is coiled (wound into ahelix) and recoiled into a compactstructure called a chromosome.Organisms have different numbers ofchromosomes-as few as two to well overa thousand. Most vertebrates fall into the20- to 80-chromosome range, and humanshave 46. Toads have 22 chromosomes, andchickens have 78. Plants and animals thatreproduce sexually generally have an evennumber of chromosomes because a set ofchromosomes is made of nearly identicalpairs. In humans, for instance, there are 23distinctly different chromosomes, and eachof those has an almost identical partner.The two similar chromoson esare calledhomologues.Every cell in every plant and animal onEarth has a complete set of chromosomesthat define the organism. 7'hechromosomes reside in the cell's nucleus.Every time a cell divides to produce twodaughter cells, the complete set ofchromosomes is duplicatecl. Each new cellis provided with a full complement ofDNA-the complete set of blueprints andoperating instructions for irssembling andmanaging one particular kind of organism.The order in which the paired bases arealigned along the length of the DNAmolecule is all important in decoding themessage to make a new organism. Just likethe 26-letter alphabet can be used to makeuntold numbers of words, depending ontheir sequence, the four-letter genetic codecan

Exploring Human Traits . In order for the class to begin to understand genetics, they will first study variation in human traits. Students will start learning about the study of heredity by surveying their own features. They will learn that they possess single gene traits with simple . Interlaced fi