Law of Segregation
During gamete formation
(meiosis), the alleles for each
gene separate from each other so
that each gamete carries only
Parent Genotype
Tt
one allele for each gene and
Let’s
look is
at plant
height
in pea plants toto
there
equal
opportunity
T
demonstrate:
pass on either allele to the
Resultin
DNA is
offspring.
g
copied
T
T t
Parent
DNA
T
T
t
t
t
t
daughter
cells
have
only one
allele
for the
height
Law of Independent
Assortment
Genes for different traits can
separate independently during the
formation of gametes (meiosis).
This means that just because a
plant is tall, it does not also
have to have all of the dominant
traits.
We will investigate this further at
a later time.
A Punnett square is a diagram that
is used to predict the probability
of a cross between 2 parents. It
determines the probability of the
offspring’s having a particular
genotype. Devised by Reginald C.
Punnett in the early 1900’s.
Parent
Genotype
Tt
In order to set up a Punnett
square, you must first understand
that parents can give only one
allele for a trait. This occurs
because of the principle of
Let’s look at plant height in
segregation
in
meiosis.
T
pea plants to demonstrate:
DNA is
copied
T t
Parent
DNA
X
T
T
T
t
t
X
t
t
Since 2 of
the 4
resulting
daughter
cells have
the same
DNA, we
only use 2
of the
possible
daughter
cells in
Parent One
Parent Genotypes: Tt
X Tt
T t
X
t
t
T
T
T
T
X
t
t
Parent Two
Parent Genotypes: Tt
X Tt
T t
T
t
t
T
T
T
X
X
T
t
t
t
Parent Genotypes: Tt X Tt
TT
tt
TT
T T
T t
T t
t t
tt
Parent Genotypes: Tt X Tt
T
t
T
T T
T t
T t
t t
t
Genotypic
Ratio: always
written as
purebred
dominant :
hybrid :
purebred
recessive and
1 TT
: 2 Tt
reduce
if :
1 tt
needed
Parent Genotypes: Tt X Tt
T
t
T
T T
Tall
T t
Tall
Phenotypic
Ratio: always
written as
dominant :
recessive and
reduce if
needed
3 Tall : 1
short
t
T t
Tall
t t
Short