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.
____/10