BIOLOGY
Chapter 11: pp. 189 - 210
10th Edition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
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Ee
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eggs
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eggs
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sperm
EE
Punnett square
E
spem
Sylvia S. Mader
Mendelian Patterns of
Inheritance
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Offspring
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Offspring
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
1
Outline
Blending Inheritance
 Monohybrid Cross



Law of Segregation
Modern Genetics
Genotype vs. Phenotype
 Punnett Square


Dihybrid Cross


Law of Independent Assortment
Human Genetic Disorders
2
Gregor Mendel


Austrian monk

Studied science and mathematics at University of
Vienna

Conducted breeding experiments with the garden pea
Pisum sativum

Carefully gathered and documented mathematical data
from his experiments
Formulated fundamental laws of heredity in early
1860s

Had no knowledge of cells or chromosomes

Did not have a microscope
3
Gregor Mendel
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Ned M. Seidler/Nationa1 Geographic Image Collection
4
Fruit and Flower of the Garden Pea
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Flower Structure
stamen
anther
filament
stigma
style
a.
carpel
ovules in
ovary
5
Garden Pea Traits Studied by Mendel
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cutting away
anthers
Brushing on
pollen from
another plant
All peas are yellow when
one parent produces yellow
seeds and the other parent
produces green seeds.
6
Blending Inheritance

Theories of inheritance in Mendel’s time:
Based on blending
 Parents of contrasting appearance produce
offspring of intermediate appearance


Mendel’s findings were in contrast with this
He formulated the particulate theory of
inheritance
 Inheritance involves reshuffling of genes from
generation to generation

7
One-Trait Inheritance

Mendel performed cross-breeding
experiments
Used “true-breeding” (homozygous) plants
 Chose varieties that differed in only one trait
(monohybrid cross)
 Performed reciprocal crosses

Parental generation = P
 First filial generation offspring = F1
 Second filial generation offspring = F2


Formulated the Law of Segregation
8
Mendel’s Monohybrid Crosses:
An Example
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
TT
P gametes
tt
T
t
F1 generation
Tt
F1 gametes
T
t
F2 generation
sperm
T
TT
Tt
Tt
tt
t
Offspring
Allele Key
T = tall plant
t = short plant
Phenotypic Ratio
3
1
tall
short
9
Law of Segregation

Each individual has a pair of factors (alleles) for
each trait

The factors (alleles) segregate (separate) during
gamete (sperm & egg) formation

Each gamete contains only one factor (allele)
from each pair

Fertilization gives the offspring two factors for
each trait
10
Modern Genetics View

Each trait in a pea plant is controlled by two
alleles (alternate forms of a gene)

Dominant allele (capital letter) masks the
expression of the recessive allele (lower-case)

Alleles occur on a homologous pair of
chromosomes at a particular gene locus

Homozygous = identical alleles

Heterozygous = different alleles
11
Homologous Chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
sister chromatids
alleles at a
gene locus
a. Homologous
chromosomes
have alleles for
same genes at
specific loci.
G
g
R
r
S
s
t
T
G
Replication
b. Sister chromatids
of duplicated
chromosomes
have same alleles
for each gene.
R
G
g
g
R
r
r
S
S
s
s
t
t
T
T
12
Genotype versus Phenotype


Genotype

Refers to the two alleles an individual has for a specific
trait

If identical, genotype is homozygous

If different, genotype is heterozygous
Phenotype

Refers to the physical appearance of the individual
13
Genotype versus Phenotype
14
Punnett Square

Table listing all possible genotypes
resulting from a cross

All possible sperm genotypes are lined up on
one side

All possible egg genotypes are lined up on the
other side

Every possible zygote genotypes are placed
within the squares
15
Punnett Square

Allows us to easily calculate probability, of
genotypes and phenotypes among the offspring
 Punnett square in next slide shows a 50% (or ½)
chance



The chance of E = ½
The chance of e = ½
An offspring will inherit:




The chance of EE =½!½=¼
The chance of Ee =½!½=¼
The chance of eE =½!½=¼
The chance of ee =½!½=¼
16
Punnett Square Showing Earlobe
Inheritance Patterns
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
Ee
Ee
eggs
E
e
EE
Ee
Ee
ee
Punnett square
spem
E
e
Offspring
Allele key
E = unattached earlobes
e = attached earlobes
Phenotypic Ratio
3
unattached earlobes
1
attached earlobes
17
Monohybrid Test cross

Individuals with recessive phenotype always have
the homozygous recessive genotype

However, individuals with dominant phenotype
have indeterminate genotype


May be homozygous dominant, or

Heterozygous
Test cross determines genotype of individual
having dominant phenotype
18
One-Trait Test Cross
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Tt
tt
Insert figure 11.7a here
eggs
t
sperm
Allele Key
T = tall plant
t = short plant
T
t
Tt
Phenotypic Ratio
1
1
tall
short
tt
a.
Offspring
19
One-Trait Test Cross
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
TT
tt
T
t
eggs
sperm
Allele Key
T = tall plant
t = short plant
Phenotypic Ratio
All tall plants
Tt
b.
Offspring
20
Two-Trait Inheritance

Dihybrid cross uses true-breeding plants differing in two
traits

Observed phenotypes among F2 plants

Formulated Law of Independent Assortment

The pair of factors for one trait segregate independently of the factors
for other traits

All possible combinations of factors can occur in the gametes
Mendel tracked each trait through two generations.




P generation is the parental generation in a breeding experiment.
F1 generation is the first-generation offspring in a breeding
experiment.
F2 generation is the second-generation offspring in a breeding
experiment
21
Two-Trait (Dihybrid) Cross
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
TTGG
P gametes
ttgg
tg
TG
F 1 generation
TtGg
eggs
TG
F 1 gametes
Tg
tG
tg
TG
TTGg
TtGG
TtGg
TTGg
TTgg
TtGg
Ttgg
TtGG
TtGg
ttGG
ttGg
Ttgg
ttGg
ttgg
Tg
sperm
F 2 generation
TTGG
tG
tg
TtGg
Offspring
Allele Key
T
t
G
g
=
=
=
=
tall plant
short plant
green pod
yellow pod
Phenotypic Ratio
9
3
3
1
tall plant, green pod
tall plant, yellow pod
short plant, green pod
short plant, yellow pod
22
Independent Assortment and Segregation
during Meiosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A
B
A
Aa
a
B
Bb
b
A
A
B
B
AB
A
B
a
a
a
b
b
b
ab
a
b
A
a
B
b
A
A
A
b
b
b
Ab
A
Parent cell has two
pairs of homologous
chromosomes.
A
Aa
a
b
bB
B
b
a
a
B
B
a
B
aB
a
B
All orientations of homologous chromosomes
are possible at metaphase I in keeping with
the law of independent
assortment.
At metaphase II, each
daughter cell has only
one member of each
homologous pair in
keeping with the law of
segregation.
All possible combinations of chromosomes
and alleles occur in
the gametes as
suggested by Mendel's
two laws.
23
Animation
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
http://get.adobe.com/flashplayer.
24
Human Genetic Disorders



Genetic disorders are medical conditions caused by
alleles inherited from parents
Autosome - Any chromosome other than a sex
chromosome (X or Y)
Genetic disorders caused by genes on autosomes are
called autosomal disorders

Some genetic disorders are autosomal dominant




An individual with AA has the disorder
An individual with Aa has the disorder
An individual with aa does NOT have disorder
Other genetic disorders are autosomal recessive



An individual with AA does NOT have disorder
An individual with Aa does NOT have disorder, but is a carrier
An individual with aa DOES have the disorder
25
Autosomal Recessive Pedigree Chart
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
I
II
III
IV
aa
A?
A?
Aa
Aa
Aa
*
Aa
aa
aa
A?
A?
A?
A?
Key
aa = affected
Aa = carrier (unaffected)
AA = unaffected
A? = unaffected
Autosomal recessive disorders
(one allele unknown)
• Most affected children have unaffected
parents.
• Heterozygotes (Aa) have an unaffected phenotype.
• Two affected parents will always have affected children.
• Close relatives who reproduce are more likely to have
affected children.
• Both males and females are affected with equal frequency.
26
Autosomal Dominant Pedigree Chart
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Aa
Aa
I
*
II
III
Aa
aa
Aa
Aa
aa
A?
aa
aa
aa
aa
aa
aa
Key
AA = affected
Aa = affected
A? = affected
(one allele unknown)
aa = unaffected
Autosomal dominant disorders
• affected children will usually have an
affected parent.
• Heterozygotes (Aa) are affected.
• Two affected parents can produce an unaffected child.
• Two unaffected parents will not have affected children.
• Both males and females are affected with equal frequency.
27
Autosomal Recessive Disorders

Tay-Sachs Disease


Cystic Fibrosis


Progressive deterioration of psychomotor functions
Mucus in bronchial tubes and pancreatic ducts is
particularly thick and viscous
Phenylketonuria (PKU)

Lack enzyme for normal metabolism of phenylalanine
28
Cystic Fibrosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H2O
Cl-
Cl-
ClCl-
H2O
H2O
Cl-
nebulizer
defective
channel
percussion
vest
thick mucus
© Pat Pendarvis
29
Methemoglobinemia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Division of Medical Toxicology, University of Virginia
30
Animation
Please note that due to differing
operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
in Presentation Mode and playing each
animation. Most animations will require
the latest version of the Flash Player,
which is available at
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Autosomal Dominant Disorders

Neurofibromatosis
Tan or dark spots develop on skin and darken
 Small, benign tumors may arise from fibrous
nerve coverings


Huntington Disease
Neurological disorder
 Progressive degeneration of brain cells

Severe muscle spasms
 Personality disorders

32
A Victim of Huntington Disease
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
JK
JJ JK
JL
JK
JL KL
a.
JL
JK JK
JL
JL
JL
JJ KL
JJ KL
JJ
KL
JJ
JK JK
JK JK KL
JK JK KL KK KL
JL
JJ
KL KL
KL
b.
a: © Steve Uzzell
33
Incomplete Dominance


Heterozygote has phenotype intermediate
between that of either homozygote

Homozygous red has red phenotype

Homozygous white has white phenotype

Heterozygote has pink (intermediate) phenotype
Phenotype reveals genotype without test cross
34
Incomplete Dominance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
R1R2
R1R2
eggs
R1
R2
sperm
R1
R1R1
R1R2
R2
R1R2
R2R2
Key
1 R1R1
2 R1R2
1 R2R2
red
pink
white
Offspring
35
Multiple Allelic Traits

Some traits controlled by multiple alleles

The gene exists in several allelic forms (but each
individual only has two)

ABO blood types

The alleles:

IA = A antigen on red cells, anti-B antibody in plasma

IB = B antigen on red cells, anti-AB antibody in plasma

I = Neither A nor B antigens, both antibodies
36
Multiple Allelic Traits
37
Pleioptropic Effects

Pleiotropy occurs when a single mutant
gene affects two or more distinct and
seemingly unrelated traits.

Marfan syndrome have disproportionately
long arms, legs, hands, and feet; a weakened
aorta; poor eyesight
38
Marfan Syndrome
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Connective
tissue defects
Skeleton
Heart and blood vessels
Chest wall deformities
Mitral valve
Long, thin fingers, arms, legs
prolapse
Scoliosis (curvature of the spine)
Flat feet
Long, narrow face
Loose joints
Enlargement
of aorta
Eyes
Lens dislocation
Severe nearsightedness
Aneurysm
Aortic wall tear
Lungs
Collapsed lungs
Skin
Stretch marks in skin
Recurrent hernias
Dural ectasia: stretching
of the membrane that
holds spinal fluid
(Left): © AP/Wide World Photos; (Right): © Ed Reschke
39
Polygenic Inheritance

Occurs when a trait is governed by two or more
genes having different alleles

Each dominant allele has a quantitative effect on
the phenotype

These effects are additive

Result in continuous variation of phenotypes
40
Frequency Distributions in Polygenic
Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
F1 generation
F2 generation
Proportion of Population
20
—
64
15
—
64
6
—
64
1
—
64
Genotype Examples
41
X – Linked Inheritance

In mammals




The X and Y chromosomes determine gender
Females are XX
Males are XY
The term X-linked is used for genes that have
nothing to do with gender



Carried on the X chromosome.
The Y chromosome does not carry these genes
Discovered in the early 1900s by a group at Columbia
University, headed by Thomas Hunt Morgan.

Performed experiments with fruit flies


They can be easily and inexpensively raised in simple laboratory
glassware
Fruit flies have the same sex chromosome pattern as humans
42
X – Linked Inheritance
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
P generation
XrY
P gametes
Xr
XRXR
XR
Y
F1 generation
XRY
XRXr
eggs
XR
F1 gametes
Xr
F2 generation
sperm
XR
XRXR
XRXr
XRY
XrY
Y
Offspring
Allele Key
XR = red eyes
Xr = white eyes
Phenotypic Ratio
females:
males : 1
1
all red-eyed
red-eyed
white-eyed
43
Human X-Linked Disorders

Several X-linked recessive disorders occur in humans:

Color blindness



Menkes syndrome



Wasting away of the muscle
Adrenoleukodystrophy



Caused by a defective allele on the X chromosome
Disrupts movement of the metal copper in and out of cells.
Muscular dystrophy


The allele for the blue-sensitive protein is autosomal
The alleles for the red- and green-sensitive pigments are on the X
chromosome.
X-linked recessive disorder
Failure of a carrier protein to move either an enzyme or very long chain fatty
acid into peroxisomes.
Hemophilia

Absence or minimal presence of a clotting factor VIII, or clotting factor IX

Affected person’s blood either does not clot or clots very slowly.
44
X-Linked Recessive Pedigree
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
XbY
XBXB
XBY
XBXb
daughter
grandfather
XBY
XbXb
XbY
XBY
XBXB
XBXb
XbY
grandson
XBXB
XBXb
XbXb
XbY
XbY
Key
= Unaffected female
= Carrier female
= Color-blind female
= Unaffected male
= Color-blind male
X-Linked Recessive
Disorders
• More males than females are affected.
• An affected son can have parents who have the
normal phenotype.
• For a female to have the characteristic, her father must
also have it. Her mother must have it or be a carrier.
• The characteristic often skips a generation from the
grandfather to the grandson.
• If a woman has the characteristic, all of her sons will
have it.
45
Muscle Dystrophy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
fibrous
tissue
abnormal
muscle
normal
tissue
(Abnormal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory, University of Rochester Medical Center; (Boy):
Courtesy Muscular Dystrophy Association; (Normal): Courtesy Dr. Rabi Tawil, Director, Neuromuscular Pathology Laboratory,
University of Rochester Medical Center.
46
Terminology

Pleiotropy



Codominance



A gene that affects more than one characteristic of an
individual
Sickle-cell (incomplete dominance)
More than one allele is fully expressed
ABO blood type (multiple allelic traits)
Epistasis


A gene at one locus interferes with the expression of a
gene at a different locus
Human skin color (polygenic inheritance)
47
Review


Blending Inheritance
Monohybrid Cross


Modern Genetics



Genotype vs. Phenotype
Punnett Square
Dihybrid Cross


Law of Segregation
Law of Independent Assortment
Human Genetic Disorders
48
BIOLOGY
Chapter 11: pp. 189 - 210
10th Edition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Parents
TT
Ee
tt
Ee
t
T
eggs
E
e
Tt
eggs
Ee
e
T
t
T
sperm
EE
Punnett square
E
spem
Sylvia S. Mader
Mendelian Patterns of
Inheritance
TT
Tt
Tt
tt
t
Ee
Offspring
ee
Offspring
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
49