Welcome Back!!!
Today you will need:
- Your journal
- The handout as you come in (QUIZ)
Genetics…continued…
Law of Segregation
Law of Independent Assortment
Dihybrid Crosses
Karyotyping
DNA Fingerprinting
The Law of Segregation
and the
Law of Independent Assortment
Law of Segregation
• During the formation of gametes (eggs or
sperm), the two alleles responsible for a
trait separate from each other.
• Alleles for a trait are then "recombined"
at fertilization, producing the genotype for
the traits of the offspring.
8
Applying the Law of Segregation
9
Law of Independent Assortment
• Alleles for different traits are
distributed to sex cells (& offspring)
independently of one another.
• This law can be illustrated using
dihybrid crosses.
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Dihybrid Cross
• Traits: Seed shape & Seed color
• Alleles: R round
r wrinkled
G green
g yellow
•
RrGg
RG Rg rG rg
x
F
O
I
L
RrGg
RG Rg rG rg
All possible gamete combinations
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Dihybrid Cross
RG
Rg
rG
rg
RG
Rg
rG
rg
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Dihybrid Cross
RG
Rg
rG
rg
RG
Rg
rG
rg
RRGG
RRGg
RrGG
RrGg
RRGg
RrGG
RrGg
RRgg
RrGg
Rrgg
RrGg
rrGG
rrGg
Rrgg
rrGg
rrgg
Round/Green:
9
Round/yellow:
3
wrinkled/Green: 3
wrinkled/yellow:
1
9:3:3:1 phenotypic
ratio
14
Let’s do it another way…
• Rule of Multiplication:
– Independent events in sequence (law of Independent Assortment)
• “and”…(x)
• What are the odds of flipping a coin 3 times and getting
tails all 3 times?
– They are ALL independent of one another…just as
traits.
• What are the odds that an offspring will be
Heterozygous for two traits if the parents are
both heterozygous for the same two traits?
• Parents: AaBb x AaBb
• What are the odds that an offspring will be
Heterozygous for both traits if the parents
genotypes are: AABb x AaBB
• What are the odds that an offspring will be
Heterozygous for 3 traits if the parents
genotypes are: AabbCC x AABbcc
Test Cross
• A mating between an individual of unknown
genotype and a homozygous recessive individual.
• Example: bbC__ x bbcc
•
•
•
•
•
•
BB = brown eyes
Bb = brown eyes
bb = blue eyes
CC = curly hair
Cc = curly hair
cc = straight hair
bC
b___
bc
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Test Cross
• Possible results:
bc
bC
b___
C
bbCc
bbCc
or
bc
bC
b___
c
bbCc
bbcc
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Summary of Mendel’s laws
LAW
DOMINANCE
SEGREGATION
INDEPENDENT
ASSORTMENT
PARENT
CROSS
OFFSPRING
TT x tt
tall x short
100% Tt
tall
Tt x Tt
tall x tall
75% tall
25% short
RrGg x RrGg
round & green
x
round & green
9/16
pods
3/16
pods
3/16
pods
1/16
pods
round seeds & green
round seeds & yellow
wrinkled seeds & green
wrinkled seeds & yellow
23
Genetic fingerprinting
13
DNA analysis can be used for catching criminals, establishing
parentage, finding how closely organisms are related and many other
applications.
The pattern of bands in a gel electrophoresis is known as a
genetic fingerprint or a ‘genetic profile’
The genetic fingerprint found in a sample of blood or other tissue (containing DNA)
is then compared to other known samples to determine it’s origin…based on how similar the
banding patterns are to each other.
A DNA sample can be obtained from the suspect using blood, cheek
epithelial cells taken from the mouth lining or even the cells clinging
to the root of a hair…as long as the tissue contains DNA
Genetic fingerprinting
DNA profiles
V
S
S1
S2
S3
V Victim
S Sample from crime scene
S1 Suspect 1
S2 Suspect 2
S3 Suspect 3
More than 20 fragments
from Suspect 1 match those
taken from the crime scene
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20
Genetic fingerprint of …
1 mother
2 child
3 possible father A
4 possible father B
There is a match between one of
the child’s restriction fragments
and one of the mother’s.
There is also a match between the
child’s other fragment and one from
possible father A.
1
2
3
4
Starting position of sample
Neither of the child’s restriction
fragments match those of possible
father B
Paternity test
Karyotype
Picture of chromosomes arranged in pairs
1.sex chromosomes –
pair #23 that determine
the sex of an individual
(XX or XY)
2.autosomes (autosomal
chromosomes) – the
remaining 22 pairs of
chromosomes