Transcript Section 10.1 Summary – pages 253-262

Bb
B
b
1. Using the picture above, explain Mendel’s Law of Segregation.
T
2. Why is
t
this Punnett
square set up
incorrectly? S
s
TT
3. Why is
this Punnett Tt
square set up
incorrectly? Tt
TT
Di-hybrid crosses
• Remember, Mendel performed experiments on pea
plants that only differed in one trait: HEIGHT
• Mendel then decided to perform another set of
crosses in which he used peas that differed from each
other only in TWO traits rather than one.
Di-hybrid crosses
These experiments were called Di-hybrid crosses:
• Di means “two” - because there were only two differences
• Hybrid because the parents were different from each other
(in two ways)
• Cross because he chose the parents to breed with each other
The pea plants were the same in every way, EXCEPT
PEA SHAPE (round, wrinkled) and PEA COLOR (yellow, green)
THE TWO DIFFERENCES
• In pea plants:
Round is Dominant “R” and Wrinkled is Recessive “r”
Yellow is Dominant “Y” and Green is Recessive “y”
RR YY
rr yy
Mendel took pure-bred plants with round yellow peas
and crossed them with pure-bred plants with
wrinkled green seeds.
• What happened with the first generation of offspring?
P1- Parents
F1- first generation of
offspring
F2- 2nd generation of
offspring
What happened with the second generation of offspring?
The Law of Independent Assortment
• The Law of Independent Assortment states:
genes for different traits—(for example, eye
shape and eye color)—
are inherited independently of each other.
bb
Bb
rr
RR
Bb
Rr
Punnett Square of Dihybrid
Cross
Gametes from RrYy parent
Gametes from RrYy parent
RY
Ry
rY
ry
RRYY
RRYy
RrYY
RRYy
RRYy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Dihybrid crosses
RrYy
RY
Ry
rY
ry
• A Punnett square
for a dihybrid
cross will need to
be four boxes on
each side for a
total of 16 boxes.
• Remember with the Law of Segregation in a
mono-hybrid cross, you had to separate the alleles
because you can only pass ONE ALLELE FOR EACH
TRAIT on to your offspring.
T
t
In a di-hybrid, you still only pass one allele PER trait to your
offspring….
But remember:
in a di-hybrid
you have two
RR YY
traits….
RY
T
TT
Tt
t
Tt
tt
RY
RY
RY
Male parent is Heterozygous for Brown eyes and Homozygous recessive for
almond
Let’s practice one together,
theneyes:
you will do one on your own.
Bb rr
Female parent is Homozygous recessive for Blue eyes and Heterozygous for
Round eyes:
bb Rr
Br
Br
br
br
bR
Bb Rr
Bb Rr
bb Rr
bb Rr
br
Bb rr
Bb rr
bb rr
bb rr
bR
Bb Rr
Bb Rr
bb Rr
bb Rr
br
Bb rr
Bb rr
bb rr
bb rr
Father, CcSs (Curly hair, Slanted eyes)
CS
Cs
cS
cs
CS
Mother, CcSs (Curly hair, Slanted eyes)
CCSS
CCSs
CcSS
CcSs
Cs
CCSs
CCss
CcSs
Ccss
cS
CcSS
CcSs
CcSs
Ccss
ccSS
ccSs
cs
ccSs
ccss
Head, C-curly, c-straight
Eyes, S-slanted, s-straight