Download CP Bio PPT\Ch.11 - Genetics\Sec 2

11-2 Probability and Punnett
Squares
11-2 Probability and Punnett Squares
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11-2 Probability and Punnett Squares
Genetics and Probability
Genetics and Probability
The likelihood that a particular event will occur is
called probability.
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11-2 Probability and Punnett Squares
Punnett Squares
Punnett Squares
Punnett squares can be used to predict
and compare the genetic variations that
will result from a cross.
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11-2 Probability and Punnett Squares
Punnett Squares
A capital letter
represents the
dominant allele.
A lowercase letter
represents the
recessive allele.
In this example,
T = tall
t = short
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11-2 Probability and Punnett Squares
Punnett Squares
Gametes produced by
each F1 parent are
shown along the top
and left side.
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11-2 Probability and Punnett Squares
Punnett Squares
Possible gene
combinations for the F2
offspring appear in the
four boxes.
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11-2 Probability and Punnett Squares
Punnett Squares
Organisms that have two identical alleles for a
particular trait are said to be homozygous(pure).
Organisms that have two different alleles for the
same trait are heterozygous(hybrid).
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11-2 Probability and Punnett Squares
Punnett Squares
All of the tall plants have the same phenotype, or
physical characteristics.
The tall plants do not have the same genotype, or
genetic makeup.
One third of the tall plants are TT, while two thirds of
the tall plants are Tt.
All of the short plants are tt.
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11-2 Probability and Punnett Squares
Punnett Squares
The plants have
different genotypes
(TT and Tt), but they
have the same
phenotype (tall).
TT
Homozygous
Tt
Heterozygous
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11-2 Probability and Punnett Squares
Probability and
Segregation
Probability and
Segregation
1/4 are TT.
1/2 are Tt
1/4 are tt.
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11-2 Probability and Punnett Squares
Probability and
Segregation
Because (T) is dominant over (t), 3/4 of the F2 plants
should be tall.
The ratio of tall plants (TT or Tt) to short (tt) plants is
3:1.
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11-2 Probability and Punnett Squares
Genetics Problems
Dominance/Recessive
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11-2 Probability and Punnett Squares
Assume white color is dominant over yellow in
squash.
If pollen from the anther of a heterozygous white
plant is placed on the pistil of a yellow plant,
show the genotypes and phenotypes of the
offspring of this cross.
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11-2 Probability and Punnett Squares
Brown eyes is dominant over blue eyes.
A brown-eyed man whose father was brown and
mother was blue married a blue-eyed women
whose parents were both brown eyed.
The couple had a blue eyed son.
Draw a pedigree chart showing the genotypes
and phenotypes of all the individuals indicated.
List all possible genotypes for people you cannot
be sure of.
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11-2 Probability and Punnett Squares
In humans, normal pigmentation is due to a
dominant gene and albinism to a recessive allele.
A normal man marries an albino women and their
first child is albino.
What are the genotypes of the 3 people?
If they have several children, what possible
genotypes and phenotypes can result and in what
proportions?
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11-2 Probability and Punnett Squares
When two green seed pea plants are crossed we
get 385 green seed plants and 115 yellow seed
plants.
When the yellow seed plants are crossed with the
original parent plants we get 975 green seed
plants and 1010 yellow seed plants.
What are the genotypes of the parents from the
P1 cross?
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11-2
Probability can be used to predict
a. average outcome of many events.
b. precise outcome of any event.
c. how many offspring a cross will produce.
d. which organisms will mate with each other.
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11-2
Compared to 4 flips of a coin, 400 flips of the
coin is
a. more likely to produce about 50% heads and
50% tails.
b. less likely to produce about 50% heads and
50% tails.
c. guaranteed to produce exactly 50% heads
and 50% tails.
d. equally likely to produce about 50% heads
and 50% tails.
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Organisms that have two different alleles for a
particular trait are said to be
a. hybrid.
b. heterozygous.
c. homozygous.
d. recessive.
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11-2
Two F1 plants that are homozygous for
shortness are crossed. What percentage of the
offspring will be tall?
a. 100%
b. 50%
c. 0%
d. 25%
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11-2
The Punnett square allows you to predict
a. only the phenotypes of the offspring from a
cross.
b. only the genotypes of the offspring from a
cross.
c. both the genotypes and the phenotypes
from a cross.
d. neither the genotypes nor the phenotypes
from a cross.
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