Transcript Punnett Square Notes

Punnett Square Notes
1. A Punnett Square is a grid for organizing genetic
information. It is VERY similar to how you
predict probability.
2. A Punnett Square indicates the PROBABILITY of
what the offspring from two individuals will
look like.
3. What are the possibilities of the offspring
between two hybrid tall pea plants?
4. What is the genotype (alleles) for a hybrid tall
pea plant?
5. What alleles can one parent possibly give to
their offspring?
6. What alleles can the other parent
give to their offspring?
Punnett Square Notes
• Place each allele at the top (male) or side
(female) of the punnett square. (drag and drop
the colored letters)
• Fill in the punnett square by reading the alleles
down & across. (drag and drop the purple
letters)
• The squares represent the possible genotypes of
the offspring from these two individuals. It does
NOT mean that there are four tall offspring
Punnett Square Notes
Tt
Tt
T
t
T
t
TT
Tt
Tt
tt
Punnett Square Notes
• The square has just given you a
probability of getting possible traits in the
offspring
• Probability of having a tt offspring
(phenotype = .25) = 25%
• Probability of having a Tt offspring
(phenotype = .50) = 50%
• Probability of having a TT offspring
(phenotype = .25) = 25%
Punnett Square Notes
• Example  What are the offspring
possibilities between a hybrid widow
peaked dad and a non-widow peaked
mom ?
• Dad is Ww
• Mom is ww
Example
• Solve the cross
Dad
W
w
Mom
w
W
Questions
• Genotype for mom =
• Genotype for dad =
• Probability of Ww offspring ( ? ) = ___
• Probability of WW offspring ( ? ) = ___
• Probability of ww offspring ( ? ) = ___
Types of Punnett Squares
There are two different types of punnett squares:
monohybrid and dihybrid.
• A monohybrid cross is exploring the possibilities
of only one trait. For example, what will the
offspring look like when a green and yellow
podded plant are crossed. You are ONLY
looking at one trait-pod color.
• A dihybrid cross is exploring the possibilities of
TWO traits. For example, what will the
offspring look like when a yellow, wrinkled pea
plant is crossed with a green, smooth pea plant.
You are looking at two traits- pea color and pea
texture.
Monohybrid Cross
• Green (Gg) x Yellow (gg)
G
g
g
g
Question: are both parents
hybrids?
Dihybrid Cross
Yellow, wrinkled (Yyrr) x Green, Smooth (yyRr)
Yr
yR
yr
yR
yr
Yr
yr
yr
Question: Are the
parents dihybrids?
Dihybrid Cross
• For a dihybrid cross, you must think of all
of the possible combination of alleles.
• For example, a yellow wrinkled plant
(Yyrr) can offer the possible allele
combinations: Yr, yr.
• This is easily determined by using the foil
method  the first times the third, the
first times the forth, the second times the
third, and the second times the forth
Problems
• What are the possible allele combinations
for a green, smooth plant (yyRr)?
• What are the possible allele combinations
for a yellow, smooth plant (YyRr)?
• What are the possible allele combinations
for a green, wrinkled plant (yyrr)?
Test cross
• A Punnett Square is used to determine the
genotype of an unknown organism. For
example, you have a tall pea plant but you
do not known if it is homozygous (TT) or
heterozygous (Tt). To determine this, you
test cross the plant with a homozygous
recessive plant- or a SHORT plant. If the
unknown is Tt, you will have some short
offspring, if it is TT, you will have all tall
offspring
Test cross
• Tall plant (TT or Tt) x short plant (tt)
T
T
T
t
t
t
t
100% Tall offspring
t
50% Tall offspring