BIOLOGY – Activity Download

Transcript
BIOLOGY – Activity
SIMULATING A ONE-FACTOR CROSS
Period 1 2 3 4 5 6 7 8
Date: _____________
Station # _____
Names _____________________
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_____________________
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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? _________________________
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3. From the data table, what were your calculated genotypic and phenotypic ratios for each
series of tosses?
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4. Which series of tosses produced the experimental ratios that were closest to predicted
ratios? Explain why.
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5. How does probability apply to the study of genetics? ____________________________
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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
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Yy
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yy
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100 tosses
YY
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Yy
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yy
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