Download Monohybrid Crosses

Do Now
1. Put modeling meiosis in bin.
2. Explain difference between heterozygous
and homozygous.
3. Explain difference between dominant and
recessive.
4. Explain difference between phenotype and
genotype.
Review: Gene
Portion of DNA
(nitrogen
bases) that
codes for a trait
Review: Allele
Two different
forms of a
gene:
Dominant
and
Recessive
Key: D = no dimples and d = dimples AND H = Unibrow and h = Two eyebrows
Identify the Genes:
Identify the Alleles:
Alleles
dd
HhDd
DD
Ddhh
Phenotype
Genotype
Punnett Square
Tool used to predict
the genotypes and
phenotypes of
offspring
What is Monohybrid Cross?
Punnett square using
only one trait.
Monohybrid
and
Mendelcross a
If purple
is dominantCross
and white
is recessive,
purebred (homozygous dominant) purple flower
Which allele is dominant?
Purple
with a white flower.
X
PP
pp
PP x pp
p
p
P
Pp
Pp
P
Pp
Pp
1st generation
Self
Pollinates
Pp x Pp
P
p
P
PP
Pp
p
Pp
pp
What do Punnett Squares represent?
A a
MEIOSIS
Possible eggs
from Mom
Possible sperm
from Dad
A
a
MEIOSIS
A
A A
A a
A a
a
A a
a a
Each square
represents the
possible
combinations
of alleles
inherited by
offspring
How to do a Punnett square
problem
1. List the symbols & alleles
T = Tall
t = Short
How to do a Punnett square
problem
2. List the Parental Cross
T = Tall
t = Short
Tt x Tt
How to do a Punnett square
problem
3. Do the Punnett square
T = Tall
T
t = Short
Tt x Tt
t
T
T T
T t
t
T t
t t
How to do a Punnett square
problem
4. List the genotypic ratio
T = Tall
T
t = Short
Tt x Tt
t
T
T T
T t
t
T t
t t
G = 1TT : 2Tt : 1tt
How to do a Punnett square
problem
5. List the phenotypic ratio
T = Tall
T
t = Short
Tt x Tt
G = 1TT : 2Tt : 1tt
P = 3 Tall:1 Short
t
T
T T
T t
t
T t
t t
How to do a Punnett square
problem
6. Answer any questions associated
with the problem.
T
t
T = Tall
t = Short
T
T T
T t
Tt x Tt
G = 1:2:1
P = 3:1
t
T t
t t
Example #1
A male that is heterozygous for purple hair is
crossed with a orange haired woman. What
chance to they have in producing a purple haired
child? Orange haired child? (Purple hair = P and
orange hair = p)
Example #2
If a man that is a purebred with big ears marries a
heterozygous woman for this trait, what is the
chance that their first child might express the
dominant trait? Big ears = B and Little ears = b
Example #3
A couple is heterozygous for the gene for big nose.
They are about to have a child and hope that it has
a small nose. Do they have a chance? How much
of a chance? B = Big nose and b = small nose