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PROBABILITY &
PUNNETT SQUARES
11-2
Interest Grabber
Section 11-2
Tossing Coins
If you toss a coin, what is the probability of getting
heads? Tails? If you toss a coin 10 times, how many
heads and how many tails would you expect to get?
Working with a partner, have one person toss a coin
ten times while the other person tallies the results on a
sheet of paper. Then, switch tasks to produce a
separate tally of the second set of 10 tosses.
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Section:
Interest Grabber Answers
1.
Assuming that you expect 5 heads and 5 tails in 10 tosses, how do the
results of your tosses compare? How about the results of your partner’s
tosses? How close was each set of results to what was expected?
Results will vary, but should be close to 5 heads and 5 tails.
2.
Add your results to those of your partner to produce a total of 20 tosses.
Assuming that you expect 10 heads and 10 tails in 20 tosses, how close
are these results to what was expected?
The results for 20 tosses may be closer to the predicted 10 heads and 10 tails.
3.
If you compiled the results for the whole class, what results would you
expect?
The results for the entire class should be even closer to the number predicted by
the rules of probability.
4.
How do the expected results differ from the observed results?
The observed results are usually slightly different from the
expected results.
PROBABILITY
____________________
is the __________
likelihood that a
particular _________________
event will occur
It can be written as a:
1/4
Fraction ____
25%
Percent ____
1:3
Ratio ____
http://www.arborsci.com/CoolStuff/CoinFlip.jpg
COIN FLIP
There are 2 possible
outcomes:
HEADS
TAILS
The chance the coin will land on either one is:
1/2
____
50%
____
1:1
____
Alleles segregate randomly just like a coin
flip. . . So can use probability to predict
outcomes of genetic crosses.
PROBABILITIES
_____ outcomes ______
PAST
DON’Taffect _________ones
FUTURE
If last coin flip was heads… there is still a 50/50
chance the next flip will be heads too.
_____________works
______
Probability
predicting
best in ___________
a ________
number of events.
large
The more flips. . . The closer results will be to
the expected 50:50 average.
DOMINANT/RECESSIVE
Dominant allele is represented by a
_____________
____________
capital letter.
(usually the first letter of the trait)
Recessive allele is represented by the SAME
____________
lower-case
_________________
letter.
T
EX: Tall = ______
NOT S for short
t
Short =______
HOMOZYGOUS
HETEROZYGOUS
When both alleles in the pair are
the _______,
SAME the organism is
_______________
HOMOZYGOUS or __________
PURE
TT
tt
EX: ____
or ___
When both alleles in the pair are
_____________,
DIFFERENT the organism is
HETEROZYGOUS or _____________
HYBRID
_________________
Ex: ____
Tt
PHENOTYPE/GENOTYPE
genetic makeup
The ________________
of an organism
is itsGENOTYPE
_____________
appearance
The ____________of
an organism is
PHENOTYPE
its _____________
MAKING A CROSS for
only a ONE
__________
GENE trait =
MONOHYBRID
CROSS
____________________
A Punnett square for
a MONOHYBRID
CROSS looks like
this:
PUNNETT SQUARES
are used to show possible offspring
from a cross between 2 parents
Parent alleles go at
_______________
top and on left side
Boxes show
T
possible
____________
offspring combinations t
___________________
T
T
STEPS FOR MAKING CROSSES
Figure out what _________________
parent alleles
1. ___________
are
Choose
Punnett square __________
size
2. ________correct__________
Put in possible_______________________
parent gametes
3. ______
Fill in boxes with _____________________
offspring combinations
4. ______
probabilities phenotypes
5. Determine ____________of_____________&
genotypes
____________
IN PEA PLANTS
Tall is dominant over short
TALL = ____
T
SHORT = ____
t
LET’S MAKE A CROSS!
PURE TALL
X PURE SHORT
PURE TALL parent
What are the parent alleles?
TT

T
HOMOZYGOUS
_________

T
What gametes
can it make?
PURE SHORT parent
What are the parent alleles?
tt

t
HOMOZYGOUS
_________

t
What gametes
can it make?
T
T
t
Tt
Tt
t
Tt
Tt
ALL
_____
of the
offspring
100
____ %
___/4
4
will be
Tt PHENOTYPE _______
TALL
GENOTYPE _____
HYBRID TALL parent
What are the parent alleles?
Tt

T
_________
HETEROZYGOUS

t
What gametes
can it make?
T
t
T
TT
Tt
t
Tt
tt
GENOTYPES
TT
¼ = _____
Tt
½ = _____
tt
¼ = _____
TALL
3/4 or ____%
75
PHENOTYPES ____
_________
____
_________
1/4or ____%
SHORT
25
PRACTICE MAKING GAMETES
for a MONOHYBRID CROSS
Tall = ____
T
t
Short = ____
R
Round seeds = ___
r
Wrinkled seeds = ___
What are the possible gametes?
Homozygous Tall parent =

What gametes can it produce?
T

TT
T
What are the possible gametes?
PURE wrinkled parent =

What gametes can it produce?
r

rr
r
What are the possible gametes?
Heterozygous Round parent =

What gametes can it produce?
R

Rr
r
What are the possible gametes?
Hybrid Tall parent =

What gametes can it produce?
T

Tt
t