Title: 11-2 Probability and Punnett Squares
111-2 Probability and Punnett Squares
2Mendel realized that the principles of
probability could be used to explain the results
of genetic crosses.He repeated a particular
cross and obtained the same results.
3Probability
- The likelihood that a particular event will occur
4A coin flip
- Possible outcomes
- Heads
- Tails
- Either outcome are equal.
5One coin flip, makes 1 chance in 2This is ½ or
50
6The probability of flipping three heads in a row
- ½ X ½ X ½ 1/8
- 1 chance in 8 flips
7The principle of probability can be used to
predict the outcome of genetic crosses.
8Punnett Square
- The gene combinations that might result from a
genetic cross.
9F1 Parents are shown along the top and left side
of the square.
It also contains the possible gene combination
for F2 offspring and the allele
10The punnett square can be used to predict and
compare the genetic variations that will result
from a cross.
11Homozygous
- Organisms that have two identical alleles for a
particular trait TT or tt. - Org. for true breeding in particular trait
12Heterozygous
- Organisms that have two different alleles for the
same trait. Tt - Organisms are hybrid for a particular trait.
13Phenotype
- Plants have the same physical characteristics.
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15Genotype
- Genetic makeup,
- Genotype of one third of the tall plants is TT
- Two thirds of the tall plant is Tt.
16Plants have the same phenotype but different
genotype.
What would happen if you cross this two plants?
Short or Tall??
17 T t
T TT 25 Tt 25
T TT 25 Tt 25
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19Probability and Segregation
- ¼ of the F2 plants have two alleles for tallness
- 2/4 or ½ have one allele for tallness
- ¼ one allele for shortness
- ¾ are going to be tall and ¼ short
- Ratio 31
20Predicted Ratio
- For each seven crosses ¾ of the plants showed the
trait controlled by the Dominant. - ¼ showed the trait controlled by the recessive
allele.
21 - The larger the number of offspring, the closer
the resulting number will get to expected values.
22Homework
- To turn in
- Make a punnett square with your family.
- Use only one trait, like eye color, tallness,
skin color, etc. - Add pictures to illustrate.
23 T t
t Tt 25 tt 25
t Tt 25 tt 25