Set
Cornell
Notes
on pg.
6.5 up
Traits
and
Probability
73
6.5 Traits
2.1 Atoms,
Ions, and Probability
and Molecules
•Topic: 6.5 Traits and
Probability
1. How did Mendel’s dihybrid crosses help
•Essential Questions:
1. How did Mendel’s
dihybrid crosses help
him develop his “Law
of Independent
Assortment”?
him develop his “Law of Independent
Assortment”?
KEY CONCEPT
The inheritance of traits
follows the rules of
probability.
6.5 Traits and Probability
KEY CONCEPT
The inheritance of traits follows the rules of
probability.
6.5 Traits and Probability
Punnett squares illustrate genetic crosses.
• The Punnett square is a grid system for predicting all
possible genotypes resulting from a cross.
– The axes represent
the possible gametes
of each parent.
– The boxes show the
possible genotypes
of the offspring.
6.5 Traits and Probability
A monohybrid cross involves one trait.
• Monohybrid crosses examine the inheritance of only one
specific trait.
Ex: color
of flower
Punnett Squares
A green pea plant (GG) is crossed with a yellow pea
plant (gg)
g
g
G
G
Gg
Gg
Gg
Gg
Geno
type=
Gg
Pheno
type=
100%
Green
1. A purple flowered plant (Pp) is crossed
with a white flowered plant (pp). What
are the genotype and phenotype of the
offspring?
2. A long tailed cat (TT) is crossed with a
short tailed cat (tt). What are the
genotype and phenotype of the
offspring? Is it possible to have short
tailed offspring?
P
p
p
Pp
p
Pp
pp
pp
T
T
t
t
Tt
Tt
Tt
Tt
G: Pp, pp
P: 50% purple
50% white
G: Tt
P: 100% long
tail
NO!!!!
6.5 Traits and Probability
• A testcross is a cross between an organism with an
unknown genotype and an organism with the recessive
phenotype.
bb
BB or Bb
Sponge Bob Genetics: Monohybrid Crosses (In Pairs)
6.5 Traits and Probability
A dihybrid cross involves two traits.
Ex: color of peas &
shape of peas
6.5 Traits and Probability
A dihybrid cross involves two traits.
Y=Yellow Pea
R= Round Pea
y= Green Pea
r= Wrinkled Pea
YyRr
•
•
•
•
YR
Yr
yR
yr
6.5 Traits and Probability
YY, Yy=Yellow Pea
RR, Rr = Round Pea
yy= Green Pea
rr= Wrinkled Pea
6.5 Traits and Probability
• Can use ratio
when determining
phenotype
• Write the # biggest
to smallest
Please figure out the
ratio.
9: Yellow smooth
3: Yellow wrinkled
3: Green smooth
1: Green wrinkled
9:3:3:1
Will follow Dominance patterns
6.5 Traits and Probability
Investigation (Pg. 72 in Notebook)
• In Pairs complete the “Allele
Combinations and Punnett Squares”
Investigation on pg. 188 in the textbook
– Read the background information
– Set up your dihybrid cross
– Answer the 4 questions
Genotype:
Ratio:
RR or Rr= purple kernels
rr= yellow kernels
TT or Tt= Smooth kernels
tt= wrinkled kernels
Rt
RT RRTt
RT
rT
rT
Genotype:
Ratio:
Rt
rt
rt
Rt
RT RRTt
Rt
RRTt
rt
RrTt
rt
RrTt
RT RRTt
RRTt
RrTt
RrTt
rT RrTt
RrTt
rrTt
rrTt
RrTt
rT
RrTt
rrTt
rrTt
•
•
Genotypes: RRTt, RrTt, rrTt
Phenotypes: 12: Purple Smooth Kernels
4: Yellow Smooth Kernels
reduce= 3:1
1. List the genotypes and phenotypes produced by this cross:
Genotypes: RRTt, RrTt, rrTt
Phenotypes: Purple smooth, yellow smooth
2. What is the genotypic ratio resulting from this cross? The phenotypic ratio?
Genotypic: 4RRTt: 8RrTt: 4rrTt = 1:2:1
Phenoypic: 12:4 purple-smooth to yellow-smooth = 3:1
3. If the genotypes for kernel texture of two plants are tt and tt, what is the probability of
their having offspring that have smooth kernels? Why?
Zero; neither parent plant has a dominant allele (T).
4. Suppose that corn plant C has a known genotype of RRTT. Could corn plants with cobs
that had some yellow and wrinkled kernels be produced by crossing Plant C with a plant
with a genotype of your choice? Why or why not?
No. All alleles are dominant, therefore no cross could lead to a
recessive phenotype.
• These findings led to
Mendel’s second law:
• The law of independent
assortment states that allele
pairs separate
independently of each
other during meiosis.
Ex:
• Hair color is inherited
independently from eye color
• Pea color is inherited
independently from pea shape
• Hair line inherited independently
from earlobes
6.5 Traits and Probability
• Probability is the likelihood that something will happen.
– predicts an average number of occurrences, not an
exact number of occurrences.
number of ways a specific event can occur
• Probability =
number of total possible outcomes
• .
Sponge Bob Genetics: Dihybrid Cross