Transcript Punnett Squares - Rutherford County Schools

Punnett
Squares
Phenotype and Genotype Practice
1. Describe the genotypes given. The first one is already done.
Example: DD homozygous, dominant
A. ss ______________________
B. Yy ______________________
C. dd __________________
D. Ww ____________________
2. In humans, brown eye color (B), is dominant over blue eye
color (b). What are the phenotypes of the following genotypes?
In other words, what color eyes will they have?
A. BB ________________________
B. bb ________________________
C. Bb ________________________
Punnett Squares
• Used to organize all the
possible combinations of
offspring from particular
parents
Making a Punnett Square
1. Draw a square; divide it into four
sections.
Making a Punnett Square
For this example, we will
show the cross between
two plants that produce
round seeds.
R=round seeds
r=oval seeds
Making a Punnett Square
2. Write the letters that represent alleles
(genes) from one parent along the top
of the box.
R
r
Making a Punnett Square
3. Write the letters that represent alleles
(genes) from the other parent along
the side of the box.
R
R
r
r
R
R
r
r
R
r
R
RR
Rr
r
Rr
rr
Example #1
G
G
g
G
Example #2
A
a
a
A
Probability
• The mathematical chance
that something will happen.
–Example: If you toss a coin,
the probability of tossing
heads is ½, or 50%. You
will get heads half the time.
What is the probability of having a
baby with blue eyes?
B
b
B
BB
Bb
B
BB
Bb
Example #1:
• The allele for a cleft chin, C, is
dominant among humans. Using
a Punnett square, what are the
results of a cross between
parents with genotypes Cc and
cc?
–What is the probability that the
offspring will have a cleft chin?
Example #2:
• This Punnett square
shows the alleles for
fur color in rabbits.
Black fur, B, is
dominant over white
fur, b.
– Given the
combinations
shown, what are
the genotypes of
the parents?
Bb
Bb
Bb
Bb
Problem #1:
?
?
T
TT
TT
t
Tt
Tt
1. What is the unknown
genotype?
2. If T represents the
allele for tall pea
plants and t
represents the allele
for short pea plants,
what is the phenotype
of each parent and
offspring?
Problem #2
• The allele for freckles, F , is
dominant among humans. Using
a Punnett square, what are the
results of a cross between
parents with genotypes FF and ff?
–What is the probability that the
offspring will have freckles?
Create a Punnett square to cross
the following:
Homozygous curly brown haired
dog x Heterozygous straight black
haired dog
Greetings
Scientists!!
• In rabbits, black fur is dominant
to white fur. If you cross a BB
male with a Bb female, what are
the possible genotypes and
phenotypes of the offspring?
What is the percent chance for
each type?
• In cabbage butterflies, white
wings are dominant to yellow
wings. If a Ww butterfly is crossed
with a ww butterfly, what are the
possible genotypes and
phenotypes of the offspring and
the percent chance for each?
• In dogs, there is a hereditary type
of deafness caused by a
recessive gene. Two dogs who
carry the gene for deafness but
have normal hearing are mated.
What are the possible genotypes
and phenotypes of their offspring
and the percent chance for each?
• In guinea pigs, short hair is
dominant over long hair. If a short
haired SS guinea pig is crossed
with a long haired ss guinea pig,
what are the possible genotypes
and phenotypes of their offspring
and the percent chance of each?
• Can you curl your tongue up on the
sides? Tongue-curling in humans is
a dominant genetic trait. Suppose a
man who is Tt for tongue-curling
marries a woman who is also Tt for
this trait. What are the possible
genotypes and phenotypes of their
children and the percent chance for
each?