bb b b 1. using the picture above, explain mendel’s law of segregation. 2. why is this punnett...
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Bb
B
b
1. Using the picture above, explain Mendel’s Law of Segregation.
2. Why is this Punnett
square set up incorrectly?
T s
t
S
3. Why is this Punnett
square set up incorrectly?
TT TT
Tt
Tt
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• Remember, Mendel performed experiments on pea plants that only differed in one trait: HEIGHT
Di-hybrid crosses
• 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.
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Di-hybrid crossesThese 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)
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Mendel took pure-bred plants with round yellow peas and crossed them with pure-bred plants with
wrinkled green seeds.
• In pea plants:
Round is Dominant “R” and Wrinkled is Recessive “r”
Yellow is Dominant “Y” and Green is Recessive “y”
THE TWO DIFFERENCES
RR YY rr yy
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• What happened with the first generation of offspring?
What happened with the second generation of offspring?
P1- Parents
F1- first generation of offspring
F2- 2nd generation of offspring
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• The Law of Independent Assortment states:
genes for different traits—(for example, eye shape and eye color)—
are inherited independently of each other.
The Law of Independent Assortment
Bb bb
rr RRBb
Rr
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• A Punnett square for a dihybrid cross will need to be four boxes on each side for a total of 16 boxes.
Dihybrid crossesDihybrid crosses
Punnett Square of Dihybrid Cross
Gametes from RrYy parentRY Ry rY ry
Ga
me
tes
from
RrY
y p
are
nt
RY
Ry
rY
ry
RRYY RRYy RrYY RrYy
RRYy RRYy RrYy Rryy
RrYY RrYy rrYY rrYy
RrYy Rryy rrYy rryy
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• 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.
TT Tt
Tt tt
T t
T
t
In a di-hybrid, you still only pass one allele PER trait to your offspring….
RR YY
But remember: in a di-hybrid you have two
traits….
R Y R Y R Y R Y
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Let’s practice one together, then you will do one on your own.Male parent is Heterozygous for Brown eyes and Homozygous recessive for
almond eyes:
Female parent is Homozygous recessive for Blue eyes and Heterozygous for Round eyes:
Bb rr
bb Rr
B r B r b r b r
b R
b R
b r
b r
Bb Rr bb RrBb Rr bb Rr
Bb rr bb rrBb rr bb rr
Bb Rr bb RrBb Rr bb Rr
Bb rr bb rr bb rrBb rr
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Head, C-curly, c-straight
Eyes, S-slanted, s-straight
Father, CcSs (Curly hair, Slanted eyes)M
oth
er,
CcS
s (C
urly
hai
r, S
lant
ed e
yes)
CS Cs cS cs
CS
Cs
cS
cs
CCSS CCSs CcSS CcSs
CCSs CCss CcSs Ccss
CcSS CcSs ccSS ccSs
CcSs Ccss ccSs ccss