Transcript Probability and Punnett Squares

Probability and Punnett
Squares
10.2 con’t.
 Punnett
squares are used to
calculate the probabilities of genetic
outcomes if the genetic makeup of
the parents is known.
 Genotype
is the genetic makeup or
the combination of alleles an
individual has.
– Ex: PP, Pp, pp, Bb, or bb
 Phenotype
is an observable trait of
an individual.
– Ex: purple, white, brown or blue…
 Testcross
are used to determine the
unknown genotype of an individual
with a dominate phenotype.
 A purple pea flower could have a
genotype PP or Pp. Crossing the
plant with a homozygous recessive
plant and observing the offspring will
identify the unknown genotype of the
purple pea.
If the unknown is PP, and a
testcross is done with a white
flower (pp) then the offspring will all
be purple (Pp).
P
P
p
Pp
Pp
p
Pp
Pp
If the unknown is Pp, and a testcross is
done with a white flower (pp) then the
offspring will be 50% purple (Pp) and 50%
white (pp).
p
p
P
p
Pp
pp
Pp
pp
 Mendel
studied 7 traits of pea plants
and determined what was dominate
and recessive. See fig 10.4 p209.
 Dihybrid cross predicts the
probability of offspring with two
traits.
 Through
dihybrid crosses, Mendel
discoved that traits randomly mix.
– Principle of independent assortment.
 Ex:
Purple flowers could be on tall or
.
short
plants. Or yellow seeds could
be wrinkled or smooth.
– The traits do not pass onto the offspring
in the same combination as in the
parents.
Ex. Tall Purple X short white
(TTPP) X (ttpp)
TP
tp TtPp
TP
TtPp
TP
TtPp
TP
TtPp
tp TtPp
TtPp
TtPp
TtPp
tp TtPp
TtPp
TtPp
TtPp
tp TtPp
TtPp
TtPp
TtPp
What is the outcome of the F1 genetation?
Ex. Tall Purple X short white
(TTPP) X (ttpp)
TP
TP
TP
TP
tp TtPp
TtPp
TtPp
TtPp
tp TtPp
TtPp
TtPp
TtPp
tp TtPp
TtPp
TtPp
TtPp
tp TtPp
TtPp
TtPp
TtPp
F1’s are all heterozygous, tall purple pea plants
 If
you crossed the F1’s, what would
be the outcome of the F2’s ?
 TtPp X TtPp ?
 You must first figure out the possible
combinations of alleles that the
parents can give to the offspring.
Remember that only one allele from
each trait is passed on.
 ???? Do you have them????
 TP,
Tp, tP and tp
 Now set up the dihybrid cross
Punnett square.
Complete the cross and find the
genotypic and phenotypic results.
TP
TP
Tp
tP
tp
Tp
tP
tp