Download GeneticsPP2.5.08

Gregor Mendel
Genetics Experiments
With Pea Plants
Mendel Noticed
 Pea Plants varied by:
height, color of flowers, position of
flowers, seed color, seed shape,
pod color, pod shape
Mendel Hypothesized
Mendel Hypothesized
 Variations in pea plant appearance was
due to something (some information)
passed along during reproduction by
the parent plants.
Mendel’s Experimental Design
Mendel’s Experimental Design
 Mendel raised pea plants to “breed
true,” I.e. tall only produced tall, short
only produced short
Mendel’s Experimental Design
 Mendel raised pea plants to “breed
true,” I.e. tall only produced tall, short
only produced short
 Mendel crossed one true-breeding
variety with the alternate true-breeding
variety, e.g. tall x short
P1
Tall X Short
P1
Tall X Short
F1
All Tall
P1
Tall X Short
F1
All Tall
F2
3/4 Tall
1/4 Short
Mendel Hypothesized
 That something was passed from
parents to offspring to determine
height; he called this an allele
P1
F1
F2
Tall
X
T
All Tall
T
3/4 Tall
T
Short
t
1/4 Short
t
Mendel Hypothesized
 That something was passed from
parents to offspring to determine
height; he called this an allele
 Further, since the t allele was “hidden”
in the F1, but reappeared in the F2,
plants must have a pair of alleles for
each trait.
P1
F1
F2
Tall
X
TT
All Tall
Tt
3/4 Tall
T?
Short
tt
1/4 Short
tt
 When an organism had a pair of alleles
the same, e.g. TT or tt, he called this
homozygous
 When an organism had an unlike pair
of alleles, e.g. Tt, he called this
heterozygous
 These terms refer to an organism’s
genotype
 The appearance of the organism he
called it’s phenotype
Practice Vocab
Ex. Plant Height
Genotype
Phenotype
Pure or Hybrid
Homozygous/
Heterozygous
More practice
Ex. Flower color
Genotype
Phenotype
Pure or Hybrid
Homozygous/
Heterozygous
Mendel proposed several
principles regarding his
findings
 If an organism is heterozygous and
only one phenotype appears, this is the
dominant phenotype, the alternate is
the recessive phenotype
 When an organism reproduces, allele
pairs must segregate and only one
member of each allele pair is passed
along to the next generation.
Solving Genetic Problems
TT
T
T
tt
T
X
t
t
t
=
T t
F1
Punnett Square
TT X tt
t
t
Genotype
4/4- Tt
T
Tt
Tt
Phenotype
4/4- Tall
T
Tt
Tt
Practice Space
Test Cross
 What is the genotype of a short pea
plant?______
 What is the genotype of a tall pea
plant?_____ or _____
 Mendel developed a way of testing
whether the tall plant is homozygous or
heterozygous. It was the test cross
Test Cross problem
T_ X tt
Independent Assortment
 The inheritance of any characteristic is
independent of the inheritance of any other
characteristic.
Ex. The inheritance of height is independent
from pea color.
Mendel provided evidence for this through
dihybrid crosses.
Dihybrid Cross
 TtPp X TtPp
To solve this problem you can use a 16
block punnett square or the Forkline
method.
16 Block Punnett Square
Fork Line Method
Ex. TtPp X TtPp
Practice with Fork Line
Method
Practicing Punnett Squares
Chromosome Options
Typical Dihybrid Cross
RrYy x RrYy
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Dihybrid Cross with Crossover

CcShsh x ccshsh
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Random Assortment
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