1. PROBABILITY & PUNNETT SQUARES 11-2

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.

3. Interest Grabber Answers
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?
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?
If you compiled the results for the whole class, what results would you expect\
How do the expected results differ from the observed results?
Results will vary, but should be close to 5 heads and 5 tails.
The results for 20 tosses may be closer to the predicted 10 heads and 10 tails.
The results for the entire class should be even closer to the number predicted by the rules of probability.
The observed results are usually slightly different from the expected results.

4. PROBABILITY
____________________ is the __________ that a particular _________________
likelihood
event will occur
It can be written as a:
Fraction ____
Percent ____
Ratio ____
1/4
25%
1:3

5. COIN FLIP 1/2 50% 1:1 capital There are 2 possible outcomes:
COIN FLIP
There are 2 possible outcomes:
HEADS TAILS
capital
The chance the coin will land on either one is:
____ ____ ____
Alleles segregate randomly just like a coin flip. . . So can use probability to predict outcomes of genetic crosses.
1/2
50%
1:1

6. PROBABILITIES _____ outcomes ______ affect _________ones
_____________works ______ in ___________ a ________ number of events.
PAST
DON’T
FUTURE
If last coin flip was heads… there is still a 50/50 chance the next flip will be heads too.
Probability
predicting
best
large
The more flips. . . The closer results will be to
the expected 50:50 average.

7. DOMINANT/RECESSIVE T t capital Dominant Recessive lower-case
_____________ allele is represented by a ____________ letter. (usually the first letter of the trait)
____________ allele is represented by the SAME
_________________ letter.
EX: Tall = ______
Short =______
capital
Recessive
lower-case T t
NOT S for short

8. HOMOZYGOUS HETEROZYGOUS
When both alleles in the pair are the _______, the organism is _______________ or __________
EX: ____ or ___
When both alleles in the pair are _____________, the organism is
_________________ or _____________
Ex: ____
SAME
HOMOZYGOUS PURE
TT tt
DIFFERENT
HETEROZYGOUS HYBRID Tt

9. PHENOTYPE/GENOTYPE
The ________________ of an organism is its _____________
The ____________of an organism is
its _____________
genetic makeup
GENOTYPE
appearance
PHENOTYPE

10. MAKING A CROSS for only a __________ trait = ____________________
ONE GENE
MONOHYBRID CROSS
A Punnett square for a MONOHYBRID CROSS looks like this:

11. PUNNETT SQUARES
are used to show possible offspring from a cross between 2 parents
_______________ go at
top and on left side
Boxes show ____________ ___________________
Parent alleles
T T T t
possible offspring combinations

12. STEPS FOR MAKING CROSSES
Figure out parent alleles
Choose Punnett size
Put in parent gametes
Fill in offspring combinations
probabilities phenotypes genotypes
1. ___________ what _________________ are
2. ________correct__________ square __________
3. ______ possible_______________________
4. ______ boxes with _____________________
5. Determine ____________of_____________& ____________

13. T t TALL = ____ SHORT = ____ IN PEA PLANTS Tall is dominant over short
LET’S MAKE A CROSS!
PURE TALL PURE SHORT X

14. PURE TALL parent What are the parent alleles?
T T _________
HOMOZYGOUS  
What gametes
can it make? T T

15. PURE SHORT parent What are the parent alleles?
t t _________
HOMOZYGOUS  
What gametes
can it make? t t

16. T t T t T t T t T t ALL _____ of the offspring ____ % ___/4 will be
100 4
T t
T t Tt
TALL
GENOTYPE _____ PHENOTYPE _______

17. HYBRID TALL parent What are the parent alleles?
T t _________
HETEROZYGOUS  
What gametes
can it make? T t

18. T t T t T t T T T t t t GENOTYPES ¼ = _____ ½ = _____ TT Tt tt 3/4 75
TALL
PHENOTYPES ____ or ____% _________
____ or ____% _________
1/4 25
SHORT

19. PRACTICE MAKING GAMETES for a MONOHYBRID CROSS
Tall = ____ Round seeds = ___
Short = ____ Wrinkled seeds = ___ T t r

20. What are the possible gametes?
Homozygous Tall parent =
What gametes can it produce?
T T   T T

21. What are the possible gametes?
PURE wrinkled parent =
What gametes can it produce? rr   r r

22. What are the possible gametes?
Heterozygous Round parent =
What gametes can it produce?
R r   R r

23. What are the possible gametes?
Hybrid Tall parent =
What gametes can it produce? Tt   T t