Dispatch
1)
Welcome to Second Semester
Take out Feb calendar and figure out how many
assignments are required this month. Come up with a
plan of attack for each assignment
2)
3)
4)
Look at your goal for this class. What do you need to
do to reach your goal?
AP Biology exam is Monday, May 14. Write that
somewhere in your notebook
Write 5 things you learned from the reading that is
due today (chapters 14-17)
5)
Pick up your final exam. Which are your strong/weak
areas? Correct at least 5 incorrect questions
•
•
•
•
•
Second Semester is different
Shorter—done after May 14th (if you have no
missing assignments)
Reviews—after school (Mon) or nutrition/lunch
(Tues). Review quizzes every Friday
Need Review book
Less labs—4 of them
Any missing assignments have to be done before
attending senior activities/AP activities
How to be successful
#1 Get organized and use TIME EFFECTIVELY
#2 Do the reading
#3 Ask questions
#4 Form study groups
#5 Do all assignments including review assignments
#6 Look over notes and powerpoints
#7 Take notes in review book and make flascards
#8 Sleep and eat enough
#9 Come to office hours to retake quizzes and FRQs (learn from past mistakes)
#10 Have confidence and a positive attitude
Chapter 14-Mendelelian
Genetics
copyright cmassengale
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Gregor Johann Mendel
(1822-1884)
Austrian monk
Studied the
inheritance of
traits in pea plants
Developed the laws
of inheritance
Mendel's work was
not recognized until
the turn of the
20th century
copyright cmassengale
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Gregor Johann Mendel
Between 1856 and
1863, Mendel
cultivated and
tested some 28,000
pea plants
He found that the
plants' offspring
retained traits of
the parents
Called the “Father
of Genetics"
copyright cmassengale
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Particulate Inheritance
Mendel stated that
physical traits are
inherited as “particles”
Mendel did not know
that the “particles”
were actually
Chromosomes & DNA
____ + ____ didn’t
know about DNA
copyright cmassengale
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Genetic Terminology
 Trait - any characteristic that
can be passed from parent to
offspring
 Heredity - passing of traits
from parent to offspring
 Genetics - study of heredity
copyright cmassengale
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Types of Genetic Crosses
 Monohybrid cross - cross
involving a single trait
e.g. flower color
 Dihybrid cross - cross involving
two traits
e.g. flower color & plant height
copyright cmassengale
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Punnett Square
Used to help
solve genetics
problems
copyright cmassengale
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copyright cmassengale
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Designer “Genes”
 Alleles - two forms of a gene
(dominant & recessive)
 Dominant - stronger of two genes
expressed in the hybrid;
represented by a capital letter (R)
 Recessive - gene that shows up less
often in a cross; represented by a
lowercase letter (r)
copyright cmassengale
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More Terminology
 Genotype - gene combination
for a trait (e.g. RR, Rr, rr)
 Phenotype - the physical
feature resulting from a
genotype (e.g. red, white)
copyright cmassengale
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Genotypes
 Homozygous genotype - gene
combination involving 2 dominant
or 2 recessive genes (e.g. RR or
rr); also called pure
 Heterozygous genotype - gene
combination of one dominant &
one recessive allele
(e.g. Rr);
also called hybrid
copyright cmassengale
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Mendel’s Pea Plant
Experiments
copyright cmassengale
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Why peas, Pisum sativum?
Can be grown in a
small area
Produce lots of
offspring
Produce pure plants
when allowed to
self-pollinate
several generations
Can be artificially
cross-pollinated
copyright cmassengale
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Reproduction in Flowering Plants
Pollen contains sperm
Produced by the
stamen
Ovary contains eggs
Found inside the
flower
Pollen carries sperm to the
eggs for fertilization
Self-fertilization can
occur in the same flower
Cross-fertilization can
occur between flowers
copyright cmassengale
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Mendel’s Experimental
Methods
Mendel hand-pollinated
flowers using a paintbrush
He could snip the
stamens to prevent
self-pollination
Covered each flower
with a cloth bag
He traced traits through
the several generations
copyright cmassengale
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How Mendel Began
Mendel
produced
pure
strains by
allowing the
plants to
selfpollinate
for several
generations
copyright cmassengale
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When he mated a round and a wrinkle
pea plant he always got all round in
the first generation and 3 times more
round than wrinkled in the second
generation.
Why? Show work
Eight Pea Plant Traits
Seed shape --- Round (R) or Wrinkled (r)
Seed Color ---- Yellow (Y) or Green (y)
Pod Shape --- Smooth (S) or wrinkled (s)
Pod Color --- Green (G) or Yellow (g)
Seed Coat Color ---Gray (G) or White (g)
Flower position---Axial (A) or Terminal (a)
Plant Height --- Tall (T) or Short (t)
Flower color --- Purple (P) or white (p)
copyright cmassengale
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copyright cmassengale
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copyright cmassengale
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Mendel’s Experimental Results
copyright cmassengale
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Why did Mendel always
get a 3:1 ratio?
Did the observed ratio match
the theoretical ratio?
The theoretical or expected ratio of
plants producing round or wrinkled seeds
is 3 round :1 wrinkled
Mendel’s observed ratio was 2.96:1
The discrepancy is due to statistical
error
The larger the sample the more nearly
the results approximate to the
theoretical ratio
copyright cmassengale
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Generation “Gap”
Parental P1 Generation = the parental
generation in a breeding experiment.
F1 generation = the first-generation
offspring in a breeding experiment. (1st
filial generation)
From breeding individuals from the P1
generation
F2 generation = the second-generation
offspring in a breeding experiment.
(2nd filial generation)
From breeding individuals from the F1
generation
copyright cmassengale
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Following the Generations
Cross 2
Pure
Plants
TT x tt
Results
in all
Hybrids
Tt
Cross 2 Hybrids
get
3 Tall & 1 Short
TT, Tt, tt
copyright cmassengale
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Law of Dominance
copyright cmassengale
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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.
copyright cmassengale
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Applying the Law of Segregation
copyright cmassengale
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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.
copyright cmassengale
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Dihybrid Cross
A breeding experiment that tracks
the inheritance of two traits.
Mendel’s “Law of Independent
Assortment”
a. Each pair of alleles segregates
independently during gamete formation
b. Formula: 2n (n = # of heterozygotes)
copyright cmassengale
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Question:
How many gametes will be produced
for the following allele arrangements?
Remember: 2n (n = # of heterozygotes)
1. RrYy
2. AaBbCCDd
3. MmNnOoPPQQRrssTtQq
copyright cmassengale
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Answer:
1. RrYy: 2n = 22 = 4 gametes
RY
Ry
rY ry
2. AaBbCCDd: 2n = 23 = 8 gametes
ABCD ABCd AbCD AbCd
aBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64
gametes
copyright cmassengale
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Dihybrid Cross
Traits: Seed shape & Seed color
Alleles: R round
r wrinkled
Y yellow
y green
RrYy
x
RrYy
RY Ry rY ry
RY Ry rY ry
All possible gamete combinations
copyright cmassengale
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Dihybrid Cross
RY
Ry
rY
ry
RY
Ry
rY
ry
copyright cmassengale
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Dihybrid Cross
RY
RY RRYY
Ry RRYy
rY RrYY
ry
RrYy
Ry
rY
ry
RRYy
RrYY
RrYy
RRyy
RrYy
Rryy
RrYy
rrYY
rrYy
Rryy
rrYy
rryy
copyright cmassengale
Round/Yellow:
Round/green:
9
3
wrinkled/Yellow: 3
wrinkled/green:
1
9:3:3:1 phenotypic
ratio
39
Dihybrid Cross
Round/Yellow: 9
Round/green:
3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1
copyright cmassengale
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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
copyright cmassengale
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Test Cross
Possible results:
bc
bC
b___
C
bbCc
bbCc
or
bc
copyright cmassengale
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 round seeds & green
pods
3/16 round seeds & yellow
pods
3/16 wrinkled seeds & green
pods
1/16 wrinkled seeds & yellow
pods
copyright cmassengale
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Incomplete Dominance
and
Codominance
copyright cmassengale
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Incomplete Dominance
F1 hybrids have an appearance somewhat
in between the phenotypes of the two
parental varieties.
Example: snapdragons (flower)
red (RR) x white (rr)
r
r
RR = red flower
rr = white flower
R
R
copyright cmassengale
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Incomplete Dominance
r
r
R Rr
Rr
R Rr
Rr
produces the
F1 generation
All Rr = pink
(heterozygous pink)
copyright cmassengale
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Incomplete Dominance
copyright cmassengale
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Codominance
Two alleles are expressed (multiple
alleles) in heterozygous individuals.
Example: blood type
1.
2.
3.
4.
type
type
type
type
A
B
AB
O
=
=
=
=
IAIA or IAi
IBIB or IBi
IAIB
ii
copyright cmassengale
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Codominance Problem
Example: homozygous male Type B (IBIB)
x
heterozygous female Type A (IAi)
IA
i
IB
IAIB
IBi
IB
IAIB
IBi
copyright cmassengale
1/2 = IAIB
1/2 = IBi
49
Another Codominance Problem
• Example: male Type O (ii)
x
female type AB (IAIB)
IA
IB
i
IAi
IBi
i
IAi
IBi
copyright cmassengale
1/2 = IAi
1/2 = IBi
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Codominance
Question:
If a boy has a blood type O and
his sister has blood type
AB,
what are the genotypes
and
phenotypes of their
parents?
boy - type O (ii)
AB (IAIB)
X
copyright cmassengale
girl - type
51
Codominance
Answer:
IA
IB
i
i
IAIB
ii
Parents:
genotypes = IAi and IBi
phenotypes = A and B
copyright cmassengale
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Sex-linked Punnets
Sex-Linked
Sex Linked—Page 2
Females are________
Males are__________
NO DISEASES ARE CARRIED ON Y CHROMOSOME
Baldness (b) is also a sex-linked trait found on the
X chromosome. If a woman is bald mates with a
man with no history of baldness in his family,
then what percent of the sons will be bald?
If fathers have the disease, the daughters are
carriers
Hemophilia (h) is caused by a recessive, sex-linked gene.
If a normal father mates with a carrier mother, what % of sons will have
hemophilia? What % of daughters will be carriers?
Hemophilia (h) is caused by a recessive, sex-linked
gene. If a father with hemophilia mates with a
normal mother, what % of sons will have
hemophilia? What % of daughters will be
carriers?
What if both parents are carriers?
Q2
Color blindness (c) is caused by a
recessive, sex-linked gene. If a father
with no colorblindness mates with a
mother who is color blind, what % of
sons will be color blind?
Sex-linked Trait Problem
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
Remember: the Y chromosome in males
does not carry traits.
Xr
Xr
RR = red eyed
Rr = red eyed
R
X
rr = white eyed
XY = male
Y
XX = female
copyright cmassengale
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Sex-linked Trait Solution:
Xr
XR
XR
Xr
Y
Xr Y
Xr
XR
Xr
Xr Y
50% red eyed
female
50% white eyed
male
copyright cmassengale
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Female Carriers
copyright cmassengale
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Pleiotrophy
Example: Sickle cell. A mutation in a gene causes multiple
symptoms
Epistasis
In genetics, epistasis is the phenomenon where the effects of one gene are
modified by one or several other genes, which are sometimes called modifier
genes.
Polygenic Inheritance
Polygenic inheritance is when a single trait is controlled by 2 or more sets of
alleles. Most human traits are polygenically inherited. Examples would be skin
and eye color. This explains how you can have several different phenotypes
for one trait and how parents can have offspring with eye color or skin color
different from what they have.
Genetic Practice
Problems
copyright cmassengale
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Breed the P1 generation
tall (TT) x dwarf (tt) pea plants
t
t
T
T
copyright cmassengale
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Solution:
tall (TT) vs. dwarf (tt) pea plants
t
t
T
Tt
Tt
produces the
F1 generation
T
Tt
Tt
All Tt = tall
(heterozygous tall)
copyright cmassengale
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Breed the F1 generation
tall (Tt) vs. tall (Tt) pea plants
T
t
T
t
copyright cmassengale
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Solution:
tall (Tt) x tall (Tt) pea plants
T
t
T
TT
Tt
t
Tt
tt
produces the
F2 generation
1/4 (25%) = TT
1/2 (50%) = Tt
1/4 (25%) = tt
1:2:1 genotype
3:1 phenotype
copyright cmassengale
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Human Genetic Diseases
1
3
4
2
2006-2007
5
6
Pedigree analysis
Pedigree analysis reveals Mendelian patterns in human inheritance
data mapped on a family tree
= male
= female
= male w/ trait
= female w/ trait
Genetic counseling
Pedigree can help us understand the past & predict the future
Thousands of genetic disorders are inherited as simple recessive traits
from benign conditions to deadly diseases
albinism
cystic fibrosis
Tay sachs
sickle cell anemia
PKU
Cystic fibrosis (recessive)
Primarily whites of
European descent
strikes 1 in 2500 births
1 in 25 whites is a carrier (Aa)
normal allele codes for a membrane protein
that transports Cl- across cell membrane
normal lung tissue
defective or absent channels limit transport of Cl- & H2O across cell membrane
thicker & stickier mucus coats around cells
mucus build-up in the pancreas, lungs, digestive tract & causes bacterial infections
without treatment children die before 5;
with treatment can live past their late 20s
Effect on Lungs
normal lungs
Chloride channel
transports salt through protein
channel out of cell
Osmosis: H2O follows Cl–
airway
Cl–
Cl– channel
H2O
cells lining
lungs
cystic fibrosis
Cl–
H2O
bacteria & mucus build up
thickened mucus
hard to secrete
mucus secreting glands
delta F508
loss of one
amino acid
Tay-Sachs (recessive)
Primarily Jews of eastern European (Ashkenazi) descent & Cajuns (Louisiana)
strikes 1 in 3600 births
100 times greater than incidence among
non-Jews
non-functional enzyme fails to breakdown lipids in brain cells
fats collect in cells destroying their function
symptoms begin few months
after birth
seizures, blindness &
degeneration of muscle &
mental performance
child usually dies before 5yo
Sickle cell anemia (recessive)
Primarily Africans
strikes 1 out of 400 African Americans
high frequency
caused by substitution of a single amino acid in hemoglobin
when oxygen levels are low, sickle-cell hemoglobin crystallizes into long rods
deforms red blood cells into
sickle shape
sickling creates pleiotropic
effects = cascade of other
symptoms
Sickle cell anemia
Substitution of one amino acid in polypeptide chain
hydrophilic
amino acid
hydrophobic
amino acid
Sickle cell phenotype
2 alleles are codominant
both normal & mutant hemoglobins are synthesized in heterozygote (Aa)
50% cells sickle; 50% cells normal
carriers usually healthy
sickle-cell disease
triggered under blood
oxygen stress
exercise
Huntington’s chorea (dominant)
Dominant inheritance
repeated mutation on end of
chromosome 4
mutation = CAG repeats
glutamine amino acid repeats in protein
one of 1st genes to be identified
build up of “huntingtin” protein in brain causing cell death
Testing…
Would you
want to
know?
memory loss
muscle tremors, jerky movements
“chorea”
starts at age 30-50
early death
10-20 years after start
1872
Genetics & culture
Why do all cultures have a taboo against incest?
laws or cultural taboos forbidding marriages between close relatives are fairly universal
Fairly unlikely that 2 unrelated carriers of same rare harmful recessive allele will meet &
mate
but matings between close relatives increase risk
“consanguineous” (same blood) matings
individuals who share a
recent common ancestor
are more likely to carry
same recessive alleles
Monohybrid
Crosses
copyright cmassengale
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P1 Monohybrid Cross
Trait: Seed Shape
Alleles: R – Round
r – Wrinkled
Cross: Round seeds
x Wrinkled seeds
RR
x
rr
r
r
R
Rr
Rr
R
Rr
Rr
Genotype: Rr
Phenotype: Round
Genotypic
Ratio: All alike
Phenotypic
Ratio: All alike
copyright cmassengale
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P1 Monohybrid Cross Review
 Homozygous dominant x Homozygous
recessive
 Offspring all Heterozygous
(hybrids)
 Offspring called F1 generation
 Genotypic & Phenotypic ratio is ALL
ALIKE
copyright cmassengale
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F1 Monohybrid Cross
Trait: Seed Shape
Alleles: R – Round
r – Wrinkled
Cross: Round seeds
x Round seeds
Rr
x
Rr
R
r
R
RR
Rr
r
Rr
rr
Genotype: RR, Rr, rr
Phenotype: Round &
wrinkled
G.Ratio: 1:2:1
P.Ratio: 3:1
copyright cmassengale
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F1 Monohybrid Cross Review
 Heterozygous x heterozygous
 Offspring:
25% Homozygous dominant RR
50% Heterozygous Rr
25% Homozygous Recessive rr
 Offspring called F2 generation
 Genotypic ratio is 1:2:1
 Phenotypic Ratio is 3:1
copyright cmassengale
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What Do the Peas Look Like?
copyright cmassengale
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…And Now the Test Cross
Mendel then crossed a pure & a
hybrid from his F2 generation
This is known as an F2 or test
cross
There are two possible
testcrosses:
Homozygous dominant x Hybrid
Homozygous recessive x Hybrid
copyright cmassengale
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F2 Monohybrid Cross
st
(1 )
Trait: Seed Shape
Alleles: R – Round
r – Wrinkled
Cross: Round seeds
x Round seeds
RR
x
Rr
R
r
R
RR
Rr
R
RR
Rr
Genotype: RR, Rr
Phenotype: Round
Genotypic
Ratio: 1:1
Phenotypic
Ratio: All alike
copyright cmassengale
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F2 Monohybrid Cross (2nd)
Trait: Seed Shape
Alleles: R – Round
r – Wrinkled
Cross: Wrinkled seeds x Round seeds
rr
x
Rr
R
r
r
Rr
Rr
r
rr
rr
Genotype: Rr, rr
Phenotype: Round &
Wrinkled
G. Ratio: 1:1
P.Ratio: 1:1
copyright cmassengale
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F2 Monohybrid Cross Review
 Homozygous x heterozygous(hybrid)
 Offspring:
50% Homozygous RR or rr
50% Heterozygous Rr
 Phenotypic Ratio is 1:1
 Called Test Cross because the
offspring have SAME genotype as
parents
copyright cmassengale
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Practice Your Crosses
Work the P1, F1, and both
F2 Crosses for each of the
other Seven Pea Plant
Traits
copyright cmassengale
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Mendel’s Laws
copyright cmassengale
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Results of Monohybrid Crosses
Inheritable factors or genes are
responsible for all heritable
characteristics
Phenotype is based on Genotype
Each trait is based on two genes,
one from the mother and the
other from the father
True-breeding individuals are
homozygous ( both alleles) are the
same
copyright cmassengale
99
Law of Dominance
In a cross of parents that are
pure for contrasting traits, only
one form of the trait will appear in
the next generation.
All the offspring will be
heterozygous and express only the
dominant trait.
RR x rr yields all Rr (round seeds)
copyright cmassengale
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