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BIOLOGY – Activity SIMULATING A ONE-FACTOR CROSS Period 1 2 3 4 5 6 7 8 Date: _____________ Station # _____ Names _____________________ _____________________ _____________________ _____________________ _____________________ INTRODUCTION In many ways, you resemble your parents, yet you probably don’t look exactly like either one of them. You inherit a mixture of characteristics from both parents. If you look closely, you will discover that each of your characteristics is not a blending of your parents’ characteristics. Instead, some of your characteristics are distinctly like your father’s and some are like your mother’s. Some of your characteristics may not appear in either parent, but they may resemble characteristics of your grandparents. In the late nineteenth century, Gregor Mendel did careful studies tracking the transmission of traits in pea plants. Mendel’s results help explain some of your observations about your own heredity. Mendel discovered that there can be two factors for each trait and that some factors for a trait are dominant while others are recessive. He also discovered that factors for each trait segregate during gamete formation and they assort independently of each other. Mendel made his discoveries with pea plants by keeping careful records of his work. In this activity, you will make observations using coins as a model of inheritance. Each coin has two sides just as each trait may have two contrasting genes. Each toss of a coin selects one side just as only one gene of a contrasting set of alleles is selected for each gamete. Tossing two coins simultaneously can be used as a model for a cross between two hybrids. When heads and tails represent contrasting alleles for a trait, the results of a toss can show which genes would combine during a cross between two gametes. OBJECTIVE To show how probability is applied to genetic crosses MATERIALS two coins plastic cup PROCEDURE 1. Use the tally sheet and data table provided to record your observations 2. In pea plants, yellow seeds (Y) are dominant over green seeds (y). Construct a Punnett square on a separate piece of paper to determine the probable color of the seeds produced by pea plants whose parents are both hybrids (Yy). Record the results in the data table. Staple your Punnett square to the back of this packet. 3. Each of the coins represent the alleles in the hybrid plant. Tossing the two coins together represents the crossing of the two hybrid plants. Let heads stand for yellow and tails stand for green. 4. Put the two coins into the cup. Place your hand over the cup and shake it at least three times. Empty the cup onto the lab table and record the results by making tally marks in the appropriate places on the tally sheet. 5. Repeat the coin toss nine more times for a total of 10 tosses. Add up the tally marks for each set of alleles and record your totals in the data table. 6. Now, repeat the tosses 100 times and record the results on the tally sheet and the totals in the data table. 7. Find the results of the 100- toss totals from 9 other teams and along with your own results add them together for a supposed 1000 tosses. Record the totals in the data table. 8. Determine the total number of seeds (tosses) with the yellow phenotype for each series of tosses and record results in the data table. 9. Using the data, calculate the genotypic and phenotypic ratios for each series of tosses. This is done by dividing the number in the ratio by the ratio’s smallest number and rounding to the nearest tenth’s place. For example, supposed you obtained 23 YY, 51 Yy and 26 yy for a series of 100 tosses. This gives you the ratio of 1 : 2.2 : 1.1 ( 23/23 = 1, 51/23 = 2.2, 26/23 = 1.1 ). OBSERVATIONS Data Table Offspring phenotype Offspring genotype Yellow Green Total Predicted Predicted Number Genotypic Phenotypic Of yellow ratio ratio YY Yy yy Seeds (YY+Yy) total total total Experimental Genotypic ratio Experimental Phenotypic ratio 10 tosses 100 tosses 1000 tosses ANALYSIS 1. Which genotype was obtained most often? ______________________________________ 2. What were your predicted genotypic and phenotypic ratios? _________________________ __________________________________________________________________________ __________________________________________________________________________ 3. From the data table, what were your calculated genotypic and phenotypic ratios for each series of tosses? _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ 4. Which series of tosses produced the experimental ratios that were closest to predicted ratios? Explain why. _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ 5. How does probability apply to the study of genetics? ____________________________ _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ 6. In the space below, construct a Punnett square for a cross between AA and Aa parents. TALLY SHEET SIMULATION OF ONE-FACTOR CROSS 10 tosses YY __________________________________________________________ Yy __________________________________________________________ yy __________________________________________________________ 100 tosses YY ___________________________________________________________ Yy ___________________________________________________________ yy ___________________________________________________________