Names______________________
_____________
Coin LAB
An experiment in probability
During the next two days we are going to test Mendel’s predictions of genetic
probability. Since we do not have the equipment or time to grow peas and get enough
data we can simulate this experiment with coins. The first day we will look at one trait
and the second day we will be exploring two traits. Since we are using coins with two
different sides, we will always be representing a hybrid cross.
Day 1: MONOHYBRID CROSS. Materials- one set of two coins (two pennies)
Select a trait that is dominant/recessive. Designate the dominant trait as heads and the
recessive trait as tails. While tossing the coins please refer to them as their traits and not
heads or tails. You will need to toss both coins. Each coin represents an allele from a
parent, so you need both in order to make an offspring. (example- you toss a head and a
head, that would be both dominant for the trait). Toss the coins a total of 100 times.
Record your actual ratios after 4, 16, 40 and 100 tosses in the data table provided.
Also calculate your expected ratios in the boxes provided. Calculate percent error.
Day 2: DIHYBRID CROSS. Materials-two sets of two coins (2 dimes and 2 nickels)
Select two traits that are dominant and recessive. Designate one trait for one of the sets
of coins and heads as dominant and tails as recessive. Do the same for the second set of
coins with a separate trait. Again refer to the coins from here on out by their traits. Toss
all four coins.(For example you toss all 4 coins, the pennies land heads and heads, and the
nickels land as head and tail, that would represent dominant, dominant for the pennies
and dominant, recessive for the nickels. Toss the coins a total of 100 times. Record your
actual ratios after 16, 50 and 100 tosses in the data table provided and calculate expected
numbers as well as percent error!
HOW DO YOU COME UP WITH THESE EXPECTED RATIOS YOU MAY ASK? I
ASK YOU WHAT DID WE DO IN CLASS THE LAST TWO DAY? Besides your
inherent drooling to my boring lectures we learned this. But lets do it again for the sake
of education.
1 TRAIT----Green is dominant, yellow is recessive. Letters would be either a G or a g.
Crossing a hybrid would be Gg x Gg
Each parent can only give one allele so either a G or a g.
G
g
G
g
Fill in the box and the expected phenotypic ratio is____________________
Now you will shake the coins one hundred times and record on a separate piece of paper
(to be included when you hand in the lab). If your expected ratio is 3:1 after 4 total
tosses what should it be after 16. Simple 5th grade math here, don’t go asking for
sophomore teacher help on this one. (to figure out the first # in the ratio you cross
multiple and divide. ¾=x/16, this will give you the first number in the ratio, figure out
the rest.
Expected
4 trials
16 trials
40 trials
100 trials
:
:
:
:
:
:
:
:
:
:
:
:
Show work for
expected
Actual
Show work for
% error
% error
Avg % error
Accept/decline
Follow Up question- Decide after each set of trials whether or not you would accept
Mendel’s genetic theory. Why or why not? Don’t just leave it as this is what is
scientifically expected, explain why it is or isn’t scientifically accepted!
Day 2- 2 Trials A dihybrid cross
Well first off what are the expected ratios. Again, I quest whether or not it is in your
notebook and then I divulge as to whether or not you understand it. I will take you
through it again. We will use Green/yellow and Smooth/wrinkled as our dominant/
recessives for the two traits. Remember it is a dihybrid cross so
it is GgSs x GgSs.
GS
Gs
gS
gs
GS
Gs
Expected
pheonotypic
ratio is:
gS
_____________
gs
Next toss the coins 100 times and figure out your coin offspring. Are they dominant,
dominant, dominant/recessive, recessive/dominant or recessive/recessive? Again
calculating expected ratios and % errors is easy. Just remember that each # is calculated
separately in the ratios! 9:3:3:1 would have 4 separate calculations!
16 trials
Expected ratio
50 trials
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
:
100 trials
:
:
:
:
:
:
:
:
:
:
:
:
:
:
Show work for
expected ratios
Actual Ratios
Show work for %
error
Percent error
Avg % error
Accept or decline
Follow Up questions: Decide after each trial whether you would accept or decline
Mendels theory or genetics and again explain why or why not. What was the most
challenging part of this experiment? What do you think was Mendel’s most challenging
aspect of his work? Please be complete in your answer.