Transcript Probability

Probability and Genetics
pg. 656-666
 Objectives:
 Describe the principles of probability and
how Mendel applied them to inheritance
 State how geneticists use Punnett squares
Vocabulary
 probability
 Punnett square
 phenotype
 genotype
 homozygous
 heterozygous
 codominance
Questions
How are punnet squares useful to
geneticists?
What is the difference between a
genotype and a phenotype?
A white cow is crossed with a red
bull. The calf is neither white nor
red, but roan. Explain how this
happens!
What was the chance of
Pettygrove winnng the coin toss?

Probability-the
liklihood that a
particular event will
occur.
Heads up
Tails up
-equally likely to occur
Math terms

Probability that coin
will land heads up is
1 in 2

Probability that coin
will land tails up is
1 in 2
1/2 or 50 %
Toss a coin 20 times
 Likely or Expect:
10 heads up / 10 tails up
 Will occur:
11 heads / 9 tails or
8 heads / 12 tails
Laws of probability is what is ‘likely’ to occur.
When you toss a coin more than once the
results of one toss do not affect the results of
the next toss.
?
Is it more
likely to
land tails ?
NO.
-Still have a 1 in 2 or 50% chance of
landing heads.
Is ‘Probability’ related to ‘Genetics’ ?
Yes!
 It can help predict the results of ‘Genetic Crosses’
 Remember Mendel ?
(the guy in a dress)
 T x T = TTTT
 txt=tttt
 T x t = TTTt
1/4 will be short ,
3/4 will be Tall

Cool Tool
Punnett Square-shows all the possible combinations of
alleles that can result from a genetic cross.




Possible combination of alleles that parents can pass on
Possible combinations of alleles that offspring can
T
t
inherit
T
TT
25%
t
Tt
25%
All by chance
4 possible combinations
Tt
25%
tt
25%
You can predict 100 % will be Red
AA
Organism with Bb alleles
B
b
B
b
BB
Bb
Bb
bb
Other Genetic Terms to use




Phenotype-physical
appearance, visible traits
ex: traits you can see
Genotype-genetic makeup ex: traits you can’t
see
Homozygous-identical
alleles ex: T T or t t, Not
purebred
Heterozygous-two
different alleles
ex: Tt or hybrid
Phenotype Genotype
Tall
TT
Tall
Tt
Short
tt
EXCEPTION
 Remember Mendel only found Dominant
and recessive genes
 Codominance-alleles are neither dominant
or recessive
 no masking takes place
 Sooooo……..
 Red Reindeer + white Reindeer =
Pink Reindeer !
YIKES !
Probability Quiz
1. An organisms’ genetic makeup , or allele
combinations.
 2. An organism’s physical appearance, or visible
traits.
 3. The likelihood that a particular event will occur.
 4. Having two identical alleles for a trait.
 5. A chart that shows all the possible
combinations of alleles that can result from a
genetic cross.
 6. Having two different alleles for a trait.
 7. A condition in which neither of two alleles of a
gene is dominant or recessive.

Questions:
8. How are punnet squares useful
to geneticists?
9. What is the difference between
a genotype and a phenotype?
10. A white cow is crossed with a
red bull. The calf is neither white
nor red, but roan. Explain how this
happens?
Answers to Probability Quiz
1.
genotype
2. phenotype
3. probability
4. homozygous
5. punnett square
6. heterozygous
7. codominance
Answers:
8.
Shows possible genetic
outcomes of offspring and the
probability of each outcome.
9. Phenotype is the physical
appearance, Genotype is the
genetic makeup.
10. Co dominance.
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