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Chapter 9
Patterns of Inheritance
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
The historical roots of genetics:
•Early 19th century: traits from mom and dad blend like paints to
form kid’s traits
______________
(1840’s) : “Father of modern genetics”
• Mendel crossed pea plants that differed in certain
characteristics (__________ ) and traced from generation to
generation; used a mathematical approach
• Why did he choose pea plants?
• Crossing of traits:
Self fertilize (____________ ) – cross pollen and egg from
same parent plant to get identical offspring
Cross Fertilize (__________ ) – cross pollen from one
parent plant with the egg of a different parent plant
Gregor mendel
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Parents
(P)
• ____ generation is truebreeding – Parent generation
– _____ generation = Hybrid
offspring of P (parents)
White
– _____ generation =
offspring of F1 plants crossed
– _____ generation =
offspring of F2 plants crossed
And so on…
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Purple
Offspring
(F1)
• Mendel hypothesized that there are alternative
forms of factors (________ ) = units that
determine heritable traits
Flower color
Purple
White
Axial
Terminal
Seed color
Yellow
Green
Seed shape
Round
Wrinkled
Flower position
Pod shape
Inflated
Constricted
Pod color
Green
Yellow
Stem length
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Tall
Dwarf
From his experimental data, Mendel deduced that an organism has two
genes (___________ ) for each inherited characteristic
• For each characteristic (trait), an organism
____________________________, one from each
parent.
Think of TRAITS as _________________ and
ALLELES as _______________ within each
category!
Examples:
P generation
(true-breeding
parents)

Purple flowers
White flowers
•Flower Color (trait)
F1 generation
All plants have
purple flowers
•Purple or White (alleles)
Fertilization
among F1 plants
(F1  F1)
F2 generation
3
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4 of plants
have purple flowers
1
4 of plants
have white flowers
__________ = physical appearance of the
allele for a specific trait (purple/white flower for flower
color trait)
_________ = genetic makeup the alleles that
represent the phenotype (one dominant, one
recessive; or 2 dominant alleles and 2 recessives)
DNA from the Beginning Animations
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• If the 2 alleles of an inherited pair are different,
then one determines the organism’s
appearance and is called the _____________
allele. (will usually show up more often!)
– The other allele has no noticeable effect on
the organism’s appearance and is called
the _______________ allele. (Is present but
does not show up in the appearance)
* If dominant allele is present, it takes
over and outweighs the recessive!
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Dominant and Recessive alleles:
In a genetic cross, CAPITAL letters are
used to represent DOMINANT alleles and
lower case letters represent the
recessive alleles.
– MUST USE SAME LETTER FOR EACH
TRAIT! (Doesn’t matter the letter you
choose!)
Example:
Flower Color (trait) T = purple, t = white
Pea Color
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
R=yellow, r =green
HOMOZYGOUS and HETEROZYGOUS
•When 2 of the SAME ALLELES are present, it is
HOMOZYGOUS for that trait.
With
homozygous,
you must clarify
hh = homozygous ____________
which alleleeither
Dominant
•When 2 DIFFERENT alleles are present, it isortermed
recessive!
HH = homozygous ___________
HETEROZYGOUS for the trait.
• Hh= __________________
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•We can look at the alleles from each parent to
determine the probability of those alleles being
passed on to offspring.
PUNNETT SQUARE:
Shows a genetic mixing (cross) of alleles from
both parents for specific traits.
Punnett Square are use to ______________
__________________ and see inheritance
patterns for specific traits!
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Trait= Flower Color
H =purple
Parent #2
H
h = white
H
h
Hh
Hh
PARENT
#1
h
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Hh
Hh
Trait= Flower Color
* If Dominant allele is present, it
takes over and outweighs the
recessive!
H =purple h = white
H
Genotype =genetic makeup
(represented by letters!)
Parent 1 = hh
homozygous recessive
H
h
Hh
Parent 2 = HH
homozygous dominant
Offspring= 100% Hh
Heterozygous
Phenotype =physical
appearance (what the letters
represent!)
Parent 1 = white
Hh
Probability of one
offspring from parent
cross!
h
Parent 2 = purple
Offspring= 100% purple
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Hh
Hh
LET’S PRACTICE!!!
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Homologous chromosomes bear the two alleles
for each characteristic
– Reside at the same __________ (point)
on homologous chromosomes
Dominant
allele
Gene loci
P
P
a
B
a
b
Recessive
allele
Genotype:
PP
Homozygous
for the
dominant allele
aa
Homozygous
for the
recessive allele
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Bb
Heterozygous
Mendel’s law of segregation
Predicts that allele
pairs from each
parent separate
(______________)
from each other
during the
production of
gametes
(sperm/eggs)
P plants
Genetic makeup (alleles)
PP
pp
All P
All p
Gametes
F1 plants
(hybrids)
All Pp
1
P
2
Gametes
1
p
2
Sperm
P
p
F2 plants Phenotypic ratio
3 purple : 1 white
P
PP
Pp
p
Pp
pp
Eggs
Genotypic ratio
1 PP: 2 Pp: 1 pp
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Mendel’s law of independent assortment
– States that alleles of a pair __________________
_________________ of other allele pairs during gamete
formation
Hypothesis: Independent assortment
Hypothesis: Dependent assortment
RRYY
P generation
Gametes
rryy
RRYY
ry
RY
rryy
Gametes

RY
ry
RrYy
RrYy
F1 generation
Sperm
Sperm
1
2 RY
1
2
ry
1
4
1
RY
2
F2 generation
Eggs
1
2
1
4
1
4
Eggs
ry
1
4
Actual results
contradict hypothesis
Figure 9.5 A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
1
4
RY
1
4
ry
1
4
RY
1
4
ry
RY
RRYY
RrYY
RRYy
RrYY
rrYY
RrYy
RrYy
ry
rrYy
Ry
RRYy
RrYy
RRyy
Rryy
RrYy
rrYy
Rryy
rryy
ry
Actual results
support hypothesis
9
16
Yellow
round
3
16
Green
round
3
16
1
16
Yellow
wrinkled
Green
wrinkled
9.8 Genetic traits in humans can be tracked through family
______________________.
Dd
Joshua
Lambert
D?
John
Eddy
Dd
Abigail
Linnell
D?
Hepzibah
Daggett
Female
dd
Jonathan
Lambert
D?
Abigail
Lambert
Dd
Elizabeth
Eddy
Male
Mating
Dd
Dd
dd
Dd
Dd
Dd
dd
Female Male
Deaf
Hearing
Figure 9.8 B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Offspring
Recessive Disorders- Most human genetic disorders are recessive
Parents
Normal
Dd

Normal
Dd
Sperm
D
D
Offspring
DD
Normal
d
Dd
Normal
(carrier)
Eggs
d
Dd
Normal
(carrier)
Figure 9.9 A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
dd
Deaf
Dominant Disorders- Some human genetic disorders are dominant
Parents
Dwarf
Dd
Normal
dd
Sperm
Achondroplasia – cause
of dwarfism
D
d
Offspring

Dd
Dwarf
d
dd
Normal
Eggs
d
Figure 9.9 B
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Dd
Dwarf
dd
Normal
9.10 New technologies can provide insight into genetic legacy
Identifying Carriers
• For an increasing number of genetic disorders, tests
are available that can distinguish carriers of genetic
disorders and can provide insight for reproductive decisions
Fetal Testing: ____________________ and
______________________________________________
(CVS) allow doctors to remove fetal cells that can be tested
for genetic abnormalities
Fetal Imaging- _________________________ uses sound
waves to produce a picture of the fetus
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
NON-MENDELIAN
GENETICS
ALL OF THE FOLLOWING ARE EXCEPTIONS
TO MENDEL’S RULES!!!
•Mendel’s principles are valid for all sexually
reproducing species, HOWEVER, genotype often
does NOT dictate phenotype in the simple way
his laws described.
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• When an offspring’s phenotype is in between the phenotypes of
its parent, it exhibits _________________________.
P generation
Red
RR

White
rr
r
R
Gametes
F1 generation
Pink
Rr
1
2
Gametes
R
1
2
r
Sperm
1
2
F2 generation
Figure 9.12 A
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
R
1
2
r
1
2
R
Red
RR
Pink
rR
1
2
r
Pink
Rr
White
rr
Eggs
• In a population, _________ _________(2 or more
options) often exist for a single trait.
Example: The ABO blood type in humans
– Involves 3 alleles of a single gene
– The alleles for A and B blood types are
____________________ and both are
expressed the phenotype
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
• __________________ - a single gene can affect a
phenotype in many ways
Individual homozygous
for sickle-cell allele
Sickle-cell (abnormal) hemoglobin
Abnormal hemoglobin crystallizes,
causing red blood cells to become sickle-shaped
Sickle cells
Clumping of cells
and clogging of
small blood vessels
Breakdown of
red blood cells
Physical
weakness
Impaired
mental
function
Anemia
Heart
failure
Paralysis
Figure 9.14
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
Pain and
fever
Pneumonia
and other
infections
Accumulation of
sickled cells in spleen
Brain
damage
Damage to
other organs
Rheumatism
Spleen
damage
Kidney
failure
• _________________ inheritance- creates a multiple
variations of phenotypes

P generation
aabbcc
(very light)

F1 generation
AaBbCc
1
8
F2 generation
AABBCC
(very dark)
1
8
AaBbCc
Sperm
1
1
1
8
8
8
1
8
1
8
1
8
1
8
1
8
Eggs
6
64
15
64
20
64
1
8
20
64
15
64
1
8
1
8
1
8
Figure 9.15
1
64
1
8
1
8
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
6
64
1
64
Skin color
15
64
6
64
1
64
THE CHROMOSOMAL BASIS OF MENDEL’S LAWS OF INHERITANCE
All round yellow seeds
(RrYy)
F1 generation
R
r
y
Y
R
Y
R
r
Y
y
Metaphase I
of meiosis
(alternative arrangements)
r
R
Y
y
r
Anaphase I
of meiosis
y
r
R
r
R
Y
y
r
R
Y
y
Metaphase II
of meiosis
y
Y
Y
y
Y
Gametes
R
R
1
4
Y
y
r
1
4
RY
F2 generation
r
r
9
ry
r
1
4
rY
Fertilization among the F1 plants
:3
Figure 9.18
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings
:3
:1
(See Figure 9.5A)
y
y
Y
R
R
1
4
Ry
• Certain genes are called _____________
GENES- tend to be inherited
together because they
reside close together on
the same chromosome.
Experiment
Purple flower
 PpLI
PpLI
Observed
offspring
Phenotypes
Long pollen
Prediction
(9:3:3:1)
Purple long
Purple round
Red long
Red round
215
71
71
24
284
21
21
55
Explanation: linked genes
PL
Parental
diploid cell
PpLI
PI
Meiosis
Most
gametes
PL
PI
Fertilization
Sperm
PL
Most
offspring
PI
PL
PL
PL
PI
PI
PI
PL
PI
PL
Eggs
PI
Figure 9.19
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3 purple long : 1 red round
Not accounted for: purple round and red long
9.20 Crossing over produces new combinations of alleles
• Crossing over can separate linked alleleS
producing gametes with recombinant
chromosomes
A
B
a
b
A
b
a
B
A B
a
b
Tetrad
Crossing over
Gametes
Figure 9.20 A
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• ___________
__________:
• Performed some
of the early
studies of crossing
over using the fruit
fly Drosophila
melanogaster.
Experiment
Black body,
vestigial
wings
Gray body,
long wings
(wild type)

GgLI
ggll
Female
Male
Offspring
Gray long
Black vestigial
Gray vestigial
Black long
965
944
206
185
Parental
phenotypes
Recombinant
phenotypes
391 recombinants
Recombination frequency =
Explanation
GgLI
(female)
G L
2,300 total offspring
G L
g l
g l
g l
g l
G l
g L
Eggs
ggll
(male)
g l
Sperm
G L
g l
G l
g L
g l
g l
g l
g l
Offspring
Figure 9.20 C
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= 0.17 or 17%
SEX CHROMOSOMES AND SEX-LINKED GENES
• In mammals, a male has one X chromosome and one Y
chromosome and a female has two X chromosomes.
• The Y chromosome has genes for the development of
testes.
• The _________________________ chromosome
allows ovaries to develop.
(male)
44
Parents’
+
diploid
XY
cells
22
+
X
Figure 9.22 A
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(female)
44
+
XX
22
+
Y
Sperm
22
+
X
44
+
XX
44
+
XY
Offspring
(diploid)
Egg
• The inheritance pattern of sex-linked genes is reflected
in females and males.
• A _________ receiving a single X-linked allele from
his mother will have the disorder
• A _________ has to receive the allele from both
parents to be affected
Female

XR XR
Male
Female
Xr Y
XR Xr

Eggs XR
Y
XR Xr
XR Y
Female
XR Y
XR Xr
XR
Figure 9.23 B
Xr Y
Sperm
XR
Y
XR XR
XR Y
XR
Xr
Y
XR Xr
XR Y
Xr Xr
Xr Y
Eggs
Eggs
R = red-eye allele
r = white-eye allele
Male

Sperm
Sperm
Xr
Male
Xr
Xr XR
Figure 9.23 C
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Xr Y
Xr
Figure 9.23 D
Sex-Linked
• Most sex-linked human disorders are due to
__________ allele and are mostly seen in
_______________.
Examples:
_____________________________
Queen
victoria
Albert
Alice
Louis
Alexandra
Figure 9.24 A
Czar
Nicholas II
of Russia
Figure 9.24 B
Alexis
Copyright © 2005 Pearson Education, Inc. Publishing as Benjamin Cummings