Download Punnett Squares

Punnett Squares
Genotype/ Phenotype
Punnett Squares
Genetics and Probability
Note:
Probability: is the possibility, or likelihood
something will occur
Point:
It can be used to predict the results of genetic
crosses
Punnett Squares
Probability
Points:
*Usually written as a fraction of as a
percentage
*Previous events do not affect future
outcomes
*Each event happens independently
Punnett Squares
Notes:
Punnett squares: are special charts that are
used to show the possible gene
combinations in a cross between two
organisms.
Reginald C. Punnett, an English geneticist,
developed the chart
Punnett Squares
Notes:
Phenotype: is the physical appearance, the
visible characteristic.
Genotype: is the actual gene makeup.
Punnett Squares
The Chart
On top:
The Female Portion
On this side:
The Male Portion
Punnett Squares
A cross between guinea
pigs. The female guinea
pig has black hair (BB)
and crosses with a white
hair male (bb). What will
the F1 (Filial) generation
look like? What is the
expressed phenotype?
What is the genotype?
Punnett Squares
What would the phenotype
and genotype be if a
female white hair guinea
pig (bb) and a black hair
guinea pig (Bb)? What
would they be if the male
were a purebred?
Punnett Squares
• Using the Punnett
Square, correctly
cross a heterozygous
blue eyed person with
a homozygous brown
eyed person.
(E=blue eyes,
e=brown eyes)
Punnett Squares
Use a Punnett square to
predict the genotypic
and phenotypic
outcome (offspring)
of a cross between
two
heterozygous/hybrid
tall (Tt) pea plants
Punnett Squares
In pea plants, yellow peas
are dominant over green
peas. Use a Punnett
square to predict the
phenotypic and genotypic
outcome (offspring) of a
cross between a plant
heterozygous/hybrid for
yellow (Yy) peas and a
plant
homozygous/purebred for
green (yy) peas.
Punnett Squares
In pea plants, yellow peas
are dominant over green
peas. Use a Punnett
square to predict the
phenotypic and genotypic
outcome (offspring) of a
cross between two plants
heterozygous for yellow
peas.
Punnett Squares
In pea plants, round peas are
dominant over wrinkled
peas. Use a Punnett
square to predict the
phenotypic and genotypic
outcome (offspring) of a
cross between a plant
homozygous for round
peas (RR) and a plant
homozygous for wrinkled
peas (rr).
Punnett Squares
In pea plants, round peas are
dominant over wrinkled
peas. Use a Punnett
square to predict the
phenotypic and genotypic
outcome (offspring) of a
cross between two plants
heterozygous for round
peas.
Punnett Squares
In dogs, there is an hereditary deafness caused by a recessive
gene, “d.” A kennel owner has a male dog that she wants
to use for breeding purposes if possible. The dog can
hear, so the owner knows his genotype is either DD or
Dd. If the dog’s genotype is Dd, the owner does not wish
to use him for breeding so that the deafness gene will not
be passed on. This can be tested by breeding the dog to a
deaf female (dd). Draw the Punnett squares to illustrate
these two possible crosses. In each case, what
percentage/how many of the offspring would be expected
to be hearing? deaf? How could you tell the genotype of
this male dog? Also, using Punnett square(s), show how
two hearing dogs could produce deaf offspring.
Punnett Squares
In humans, brown eyes (B) are
dominant over blue (b). A
brown-eyed man marries a
blue-eyed woman and they
have three children, two of
whom are brown-eyed and one
of whom is blue-eyed. Draw
the Punnett square that
illustrates this marriage. What
is the man’s genotype? What
are the genotypes of the
children?
Punnett Squares
•
•
Punnett square for a Dihybrid Cross
In the pea plant, two characteristics for the peas, shape and color, will be
used to demonstrate an example of a dihybrid cross in a punnett square. R
is the dominant gene for roundness for shape, with lower-case r to stand
for the recessive wrinkled shape. Y stands for the dominant yellow pea,
and lower-case y stands for the recessive green color. By using a punnett
square (the gametes are RY, Ry, rY, and ry):
RY
RY
Ry
rY
ry
RRYY
Ry
rY
ry
Punnett Squares
• Di-hybrid Crosses:
– You have to look at the options if it is Rr and
Tt the parent can pass on RT, Rt, rT, rt.
• The result is a 9:3:3:1 phenotypic ratio, as
shown by the colors, where yellow
represents a round yellow (both dominant
genes) phenotype, green representing a
round green phenotype, orange
representing a wrinkled yellow phenotype,
and blue representing a wrinkled green
phenotype (both recessive genes).
Punnett Squares
Monohybrid, Dihybrid, Trihybrid Cross
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