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
1
Blending Inheritance

Theories of inheritance in Mendel’s time:
Based on blending
 Parents of contrasting appearance produce
offspring of intermediate appearance

2
Gregor Mendel
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Mendel’s findings were in
contrast with this
• Particulate theory of
inheritance
• Involves reshuffling of
genes from generation
to generation
© Ned M. Seidler/Nationa1 Geographic Image Collection
3
Law of Segregation

Each individual has a pair of alleles for each trait

The alleles segregate (separate) during gamete
formation

Each gamete contains only one allele from each
pair

Fertilization gives the offspring two factors for
each trait
4
Mendel’s Monohybrid Crosses:
An Example
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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
5
Homologous Chromosomes
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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
7
Punnett Square

Can 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 =½x½=¼
The chance of Ee =½x½=¼
The chance of eE =½x½=¼
The chance of ee =½x½=¼
11
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
12
Monohybrid Test cross

Test cross determines genotype of individual
having dominant phenotype

Based on the knowledge that individuals with
recessive phenotype always known homozygous
recessive genotype
13
Monohybrid Test cross

However, individuals with dominant phenotype
have unknown genotype

May be homozygous dominant, or Heterozygous
14
Two-Trait Inheritance

Dihybrid cross uses
true-breeding plants
differing in two traits
 Observed
phenotypes among
F2
15
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
16
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17
Sample Dihybrid Problem

Tall is dominant to short and purple is
dominant to white in pea plants. Cross two
plants that are heterozygous for both traits.
18
Chi-Square

Chi-Square Tutorial

In the garden pea, yellow cotyledon color is
dominant to green, and inflated pod shape is
dominant to the constricted form. Considering
both of these traits jointly in self-fertilized
dihybrids, the progeny appeared in the following
numbers:
 193 green, inflated; 184 yellow constricted
 556 yellow, inflated; 61 green, constricted
 Do these genes assort independently? Support
your answer using Chi-square analysis.
19
Gene Linkage
1. How are the scientists results different
from Mendel’s work?
 2. How did they explore their results?
 3. How did the scientists explain their
findings?
 Genetic linkage is very strong for genes
which are located close to each other on
the same chromosome. What happens in
the case of two genes which are far apart
on the same chromosome?

20
Are all alleles completely dominant or
recessive?

Incomplete Dominance
The heterozygous is in between the
homozygous individuals.
 Phenotype reveals genotype without test cross

21
Example

Cross two pink flowers. What genotypes
and phenotypes are possible?
22
Co-Dominant

Both alleles are expressed in the
phenotype.
23
Example

In humans blood type AB (IAIB) is
codominant. What blood types are
possible if two people with AB blood type
have children?
24
Do any genes have more than two
alleles?

Multiple Alleles
The gene has several allelic forms
 But each individual still receives two

25
Practice

Mom is Type A and Dad is Type B, what
are all the possible blood types for their
children?
26
Is each phenotypic trait influenced by
only one gene?

Polygenic
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

27
28

For genes that are on the X chromosome in
humans and other mammals, what are the
differences in inheritance for males vs.
females?
29
X – Linked Inheritance

In mammals



The X and Y
chromosomes
determine gender
Females = XX
Males = XY
30

X-linked = genes that
have nothing to do with
gender


Carried on the X
chromosome and the Y
does not have these
genes.
Discovered in the early
1900s by a group at
Columbia University,
headed by Thomas
Hunt Morgan.
31
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.
32
Practice

Cross a male hemophiliac with a female
whose father was a hemophiliac. What are
the possible genotypes and phenotypes of
their children?
33
Human Genetic Disorders/Pedigrees

Autosomal – any gene not on the sex
chromosomes

Dominant genetic disorder (brittle bone)


AA and Aa have the disorder
Recessive genetic disorder (cystic fibrosis)

aa has the disorder
34
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.
35
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.
36
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
37
Methemoglobinemia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Division of Medical Toxicology, University of Virginia
38
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

39
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
40
Marfan Syndrome
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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
41
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.
42
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.
43
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)
44
Review


Blending Inheritance
Monohybrid Cross


Modern Genetics



Genotype vs. Phenotype
Punnett Square
Dihybrid Cross


Law of Segregation
Law of Independent Assortment
Human Genetic Disorders
45
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
46