Chapter 12
Mendel, Genes, and
Inheritance
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Genetic Variation in Rabbits
© 2017 Cengage Learning. All Rights Reserved.
Why It Matters …
• A genetic disorder called sickle-cell anemia
develops when a person inherits two mutated
copies of a gene (one from each parent) that
codes for a subunit of hemoglobin
• When oxygen is low, the altered hemoglobin forms
crystal-like structures that push red blood cells into
a sickle shape
• The altered protein differs from the normal protein
by just a single amino acid
© 2017 Cengage Learning. All Rights Reserved.
Sickle-Cell Anemia
Dr. Stanley Flegler/Visuals Unlimited
B. A
sickled red blood cell
Dr. Stanley Flegler/Visuals Unlimited
A. A normal red blood
cell
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Gregor Mendel
M. Hofer/National Library of Medicine
• Mendel discovered the
fundamental rules that
govern inheritance
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12.1 The Beginnings of Genetics:
Mendel’s Garden Peas
• Until about 1900, scientists believed in the
blending theory of inheritance
• In the 1860s, Gregor Mendel studied patterns of
inheritance by experimenting with garden peas
• Mendel studied specific heritable features
(characters) that had alternative forms (character
differences or traits)
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The Beginnings of Genetics (cont'd.)
• Mendel established that characters are passed to
offspring in the form of discrete hereditary factors
(genes)
• Mendel observed that many parental traits appear
unchanged in offspring – others disappear in one
generation to reappear unchanged in the next
• The inheritance patterns he observed are the
result of the segregation of chromosomes to
gametes in meiosis
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True-Breeding Garden Peas
• Mendel chose the garden pea (Pisum sativum) for
his genetics experiments
• Normally, pea plants self-fertilize (self-pollinate)
• Mendel prevented self-fertilization by cutting off
the anthers, and used pollen from a different plant
to fertilize the flowers (cross-fertilization or
cross-pollination)
• To begin his experiments, Mendel chose pea
plants that were true-breeding (pure-breeding)
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Research Method: Crossing Peas
Pea plant
Ovary, containing ovules in
which eggs—female gametes—
are produced and
fertilization occurs,
leading to the development
of seeds.
Carpel—female
structure; lower
end contains the
ovary with the
ovules in which
eggs (female
gametes) are
produced.
Stigma, the
upper end of
the carpel
where pollen
lands and begins
the
fertilization
process.
Stamen—male
structure;
ends
with an
anther.
Anthers, structures
where pollen—male
gametes are
produced.
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Research Method: Crossing Peas
Male parent
Female parent
F1 generation
seeds
F1 generation
adult plant
Seed
Transfer
pollen from
male parent
onto stigma
of female
parent.
1. Remove the anthers from one of the
parents (the
white-flowered plant)
to prevent self-fertilization.
Transfer pollen from the male parent
(the purple-flowered plant) onto the
stigma of the white flower (the female
parent). This results in crossfertilization, the fertilization of
one plant with pollen from another.
Anthers
are
removed
.
2. The cross-fertilized plant produces
seeds. Seeds may be scored for seed
traits, such as round vs. wrinkled
shape. Seeds are grown into adult
plants. Plants may be scored for
adult traits, such as purple vs.
white flower color.
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Crosses with One Character
• Mendel crossed true-breeding plants that had
purple flowers with true-breeding plants that had
white flowers
purple ♂ X white ♀
• He also carried out a reciprocal cross in which the
two parents were switched
white ♂ X purple ♀
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Generations
• True-breeding plants used in an initial cross are
called the parental or P generation
• The first generation of offspring from a cross is
called the filial or F1 generation
• Self-pollination of individuals from the F2
generation produces an F2 generation
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Crosses with One Character (cont'd.)
• Plants that grew from Mendel’s F1 seeds all had
purple flowers, as if the trait for white flowers had
disappeared
• In the F2 generation, the missing trait reappeared
– both traits were present among the offspring
• About ¾ of the plants that grew from F2 seeds had
purple flowers, but ¼ had white flowers (a ratio of
3:1)
• For each character Mendel tested, the ratio of the
two traits in the F2 generation was close to 3:1
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Mendel’s Crosses with Peas
Characte
r
Traits
crossed
F
F
1
2
Flower
color
purple ×
white
All
purple
705
purple
Seed
shape
round ×
wrinkled
All
round
Seed
color
yellow ×
green
All
yellow
Pod
shape
inflated ×
constricted
Pod
color
green ×
yellow
Flowe
r
posit
ion
axial (along
stems) ×
terminal (at
tips)
Stem
length
tall ×
dwarf
All
inflate
d
Rati
o
224
white
3.15
: 1
5,474
round
1,850
wrinkled
2.96
: 1
6,022
yellow
2,001
green
3.01
: 1
299
constricte
d
2.95
: 1
428
green
152
yellow
2.82
: 1
All
axial
651
axial
207
terminal
3.14
: 1
All
tall
787
tall
All
green
882
inflated
277
dwarf
2.84
: 1
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Mendel’s Three Conclusions
• Adult plants carry a pair of factors (alleles of
genes) that govern the inheritance of each trait
• If an individual’s pair of genes consists of different
alleles, one allele is dominant over the other,
which is recessive
• Pairs of alleles segregate as gametes are formed;
half the gametes carry one allele, and the other
half carry the other allele (Mendel’s Principle of
Segregation)
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Key Genetics Terms
• Homozygote
• A true-breeding individual: both alleles of a gene
are the same
• Produces only one type of gamete
• A homozygote is said to be homozygous for the
particular allele of the gene
• Heterozygote
• An individual with two different alleles of a gene
• Produces two types of gametes – half have one
allele, half have the other allele
• A heterozygote is said to be heterozygous for the
pair of different alleles of a gene
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Key Genetics Terms (cont'd.)
• Monohybrid
• An F1 heterozygote produced from a cross that
involves a single character
• Monohybrid cross
• A cross between two individuals that are each
heterozygous for the same pair of alleles
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Genotype and Phenotype
• Genotype refers to the genetic constitution of an
organism in terms of genes and alleles
• Phenotype refers to the organism’s appearance
• Example: Two alleles for flower color: P = purple
(dominant), and p = white (recessive)
• Genotypes PP (homozygous dominant) and Pp
(heterozygous) produce the purple phenotype
• Genotype pp (homozygous recessive) produces
the white phenotype
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Experimental Research: Mendel's Principle of
Segregation
1. P generation
P is the dominant
allele for purple;
the true-breeding
purple-flowered
parent has the PP
combination of
alleles. The plant
is homozygous for
2. Haploid
the P allele.
gametes
The two alleles
separate during
gamete formation:
only gametes with
the P allele are
produced in a PP
plant.
Purpl
e
Whit
e
×
P
P
P
p
p
p
p is the recessive
allele for white;
the true breeding
white-flowered
parent has the pp
combination of
alleles. The plant
is homozygous for
the p allele.
The two alleles
separate during
gamete formation:
only gametes with
the p allele are
produced in a pp
plant.
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Experimental Research: Mendel's Principle of
Segregation (cont'd.)
3. F1
generation
Gamete from
parent with
white flowers
p
Gamete
from
parent
with
purple
flowers
P
P
p
Fusion of the P gamete from
the
purple-flowered parent with
the p gamete from the whiteflowered parent produces an
F1 generation of all Pp
plants, which have purple
flowers because the P allele
is dominant to the p allele.
Because they have two
different alleles of a gene,
the plants are said to be
heterozygous for that gene.
The F1 heterozygote is called
a monohybrid.
© 2017 Cengage Learning. All Rights Reserved.
Experimental Research: Mendel's Principle of
Segregation (cont'd.)
4. F1 × F1
self
×
P
p
5. F2
generation
P
p
Gametes
from
Pp Fl plant
P
Mendel now performed
a
monohybrid cross by
allowing
F1 purple Pp plants
to self and
produce the F2
generation.
P
P
Gametes
from
Pp F1 plant
P
P
P
p
P
p
P
P
p
The P and p gametes
fused to produce the
F2generation.
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Probability
• Probability is the mathematical possibility that an
outcome will occur if it is a matter of chance – as
in the random fertilization of an egg by a sperm
• A certain outcome has a probability of 1, and an
impossible outcome has a probability of 0
• If two different outcomes are equally likely, we
divide the probability of one outcome by the total
number of possible outcomes (probability of a
head when flipping a coin is ½)
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The Product Rule in Probability
• When two or more events are independent, we
calculate the probability that they will occur in
succession using the product rule (multiply their
individual probabilities)
• Example: Flipping a coin two times
• Probability of getting heads on the first flip = ½
• Probability of heads on the second flip = ½
• Probability of getting two heads in a row = ½ X ½
=¼
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Rules of Probability
Second toss
Probability is
1/2
Probability is
First
1/2
toss
Probability is
1/2
Probability is
1/2
1/2 × 1/2 =
1/4
1/2 × 1/2 =
1/4
1/2 × 1/2 = 1/4
1/2 × 1/2 =
1/4
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The Sum Rule in Probability
• When there are two or more different ways of
obtaining the same outcome, we determine the
probability using the sum rule (add the individual
probabilities)
• Example: Getting a head and a tail in two flips of a
coin
• There are two ways this can happen: head/tail
(probability ¼) and tail/head (probability ¼)
• Probability of 1 head and 1 tail in either order = ¼ +
¼=½
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Probability in Mendel’s Crosses
• Probability of obtaining purple flowers in the cross
Pp X Pp:
• Two ways to get purple flowers – genotypes PP
and Pp
• Add the individual probabilities: ¼ PP + ½ Pp = ¾
• The Punnett square method is also used to
determine genotypes of offspring and their
expected proportions
• The probability of obtaining gametes with each type
of allele is written at the top for one parent, and on
the side for the other parent
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Gametes from F1 purple Pp plant
Gametes
from F1
purple Pp
plant
Stepped Art
Testcrosses
• A testcross is a cross between an individual with
the dominant phenotype and a homozygous
recessive individual
• Geneticists use a testcross to determine whether
an individual with a dominant trait is a
heterozygote or a homozygote
• If half of the offspring have the dominant trait and
half the recessive trait, then the tested individual is
a heterozygote
• If all offspring have the dominant trait, the tested
individual is a homozygote
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Experimental Research: Genetic Crosses
le plant X true-breeding white plant
Fl
(heterozygous)
purple-flowered
plant from a cross
of a true-breeding
purple-flowered
plant and a
2.
true
Offspring
breeding
white-flowered
plant
Whit
e
Purpl
e
X
P
p
pp
True-breeding
(homozygous) whiteflowered plant
Gamete from pp
plant
1
p
1/2 P
Gametes from
Pp plant
1/2 Pp
1/2 p
1/2 pp
The heterozygous Pp
plant produces two
types of gametes: 1/2
are P and 1/2 are p.
The homozygous pp plant
Produces one type of
gamete: 1 p.
Combination of the
gametes produces the
offspring.
© 2017 Cengage Learning. All Rights Reserved.
Experimental Research: Genetic Crosses
(cont'd.)
1. True-breeding purple plant X true-breeding white plant
Purple
White
Homozygou
spurpleflowered plant
True-breeding
white-flowered plant
X
PP
pp
2. Offspring
Gamete from
pp plant
1
p
Gamete from 1
P
PP plant
1 Pp
The homozygous PP plant produces one
type of gamete: 1 P. The homozygous pp
plant produces one type of gamete: 1 p.
Combination of the gametes produces
the offspring.
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Crosses Involving Two Characters
• Mendel next experimented with crosses in which
two characters (seed shape and seed color) were
involved
• For seed shape, round is dominant to wrinkled:
• RR or Rr genotypes produce round seeds
• The rr genotype produces wrinkled seeds
• For seed color, yellow is dominant to green:
• YY or Yy genotypes produce yellow seeds
• The yy genotype produces green seeds
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Key Genetic Terms
• Dihybrid
• An F1 that is produced from a cross that involves
two characters and is heterozygous for each of the
pairs of alleles of the two genes involved
• Example: Aa Bb, where genes A and B control
different traits (upper case = dominant, lower case
= recessive)
• Dihybrid cross
• A cross between two individuals that are each
heterozygous for the pairs of alleles of two genes
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Crosses Involving Two Characters (cont'd.)
• Mendel crossed a true-breeding plant with round,
yellow seeds (RR YY) with a true-breeding plant
with wrinkled, green seeds (rr yy) through to the F2
generation
• The F2 generation showed a phenotypic ratio of
9:3:3:1
• The allele for seed shape that the gamete receives
(R or r) has no influence on which allele for seed
color it receives (Y or y) and vice versa – the two
events are independent
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Experimental Research: Independent
Assortment
1. P generation
Round,
yellow
Wrinkled,
green
X
RR YY
rr
yy
R Y
r
y
2. Haploid gametes
3. F1
generation
Round and
yellow
Rr
Yy
© 2017 Cengage Learning. All Rights Reserved.
Experimental Research: Independent
Assortment (cont'd.)
4. F1 X F1
self
Round,
yellow
Round,
yellow
X
Rr
Yy
5. F2
generation
¼ R Y
Rr
Yy
Gamete
s
¼ r y
¼ R Y
¼
r
y
¼ R Y
1/16 RR YY 1/16 1/16
RR
Rr 1/16
Yy
YY
Rr Yy
¼ R Y
Gamete
s
(eggs)
1/16 RR 1/16 RR 1/16 Rr 1/16 Rr
Yy
¼
yy
Yy
r y
1/16 Rr 1/16 Rr 1/16
YY
¼
yy
Yy
YY
rr1/16 rr
Yy
r y
1/16 Rr 1/16 Rr 1/16 rr 1/16 rr
Yy
yy
Yy
yy
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Mendel’s Principle of Independent Assortment
• Mendel showed that traits of different characters
were distributed to offspring independently, not
inherited together – a property known as
independent assortment
• Mendel’s Principle of Independent Assortment
• The alleles of genes that govern two characters
assort independently during formation of gametes
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Molecular Insights: Genes and Dwarfing
• Research Question: What is the function of
Mendel’s Le gene in controlling stem length?
• Conclusion: The methods of molecular biology
allowed contemporary researchers to study a gene
first studied genetically in the mid-nineteenth
century. The findings leave no doubt that the gene
codes for an enzyme that catalyzes formation of a
plant hormone responsible for causing plant stems
to elongate.
© 2017 Cengage Learning. All Rights Reserved.
Foundation of the Field of Genetics
• Mendel’s findings in the 1860s anticipated in detail
the patterns by which genes and chromosomes
determine inheritance
• His work was overlooked until the early 1900s,
when investigators performed similar experiments
and reached the same conclusions
• Meiosis, which related Mendel’s “factors” to cell
structures, was not discovered until the 1890s
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Sutton’s Chromosome Theory of Inheritance
• Walter Sutton recognized the similarities between
Mendel’s genes and the behavior of
chromosomes:
• Chromosomes occur in pairs, as do alleles of each
gene
• Chromosomes of each pair are separated and
delivered singly to gametes, as are alleles of a
gene
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Sutton’s Chromosome Theory of Inheritance
(cont'd.)
• Walter Sutton recognized the similarities between
Mendel’s genes and the behavior of
chromosomes:
• Separation of a chromosome pair in meiosis is
independent of the separation of other pairs, as in
independent assortment in Mendel’s dihybrid
crosses
• In fertilization, one member of each chromosome
pair is derived from the male parent, and one from
the female parent – an exact parallel with the two
alleles of a gene
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Behavior of
chromosomes in meiosis
Meiosis in male or female
diploid parent
Behavior of genes and alleles in meiosis
and correspondence to Mendel’s principles
Diploid nucleus
before replication
Chromosomes occur
in pairs in diploid
individuals
Alternative path 2
Alternative path 1
Alleles of genes occur in
pairs in diploid individuals
(R/r is a pair of alleles and
Y/y is another)
Chromosomes
replicate before
meiosis (follows either
left or right path)
Metaphase I
of meiosis
During chromosome
separation, the
chromosomes
of different
pairs segregate
independently
Two meiotic divisions
separate chromosome
pairs and deliver them
singly to gametes
First meiotic
division
Principle of segregation:
Two alleles of a gene
segregate from each other
during gamete formation
Second meiotic
division
Principle of independent
assortment: During the
segregation of alleles into
gametes, alleles of
different pairs assort
independently
Gametes
¼•R Y
¼•r y
¼•R y
¼•r Y
Stepped Art
The Chromosome Theory of Inheritance
• Sutton correctly concluded that genes and their
alleles are carried on the chromosomes, known as
the chromosome theory of inheritance
• The particular site on a chromosome at which a
gene is located is called the locus (plural, loci) of
the gene
• The locus is a particular DNA sequence that
typically encodes a protein responsible for a
phenotype
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A Locus
• Different alleles consist
of differences in DNA
sequence of a gene,
which may result in
functional differences in
the protein encoded by
the gene
Homologous
chromosome pair
(unreplicated)
Allele a
Allele A
of gene
of gene
A
a
Gene locus
(the
location of a
gene on a
chromosome)
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Human Traits with Mendelian Inheritance
Patterns
C.
St Bartholomew’s Hospital/Science Source
Friedrich Stark/Alamy
B.
David R. Frazier/Science Source
A.
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STUDY BREAK 12.1
1. Two pairs of traits are segregating in a cross.
Two parents produce 156 progeny that fall into 4
phenotypes. The numbers of offspring in the 4
phenotypes are 89, 31, 28, and 8. What are the
genotypes of the two parents?
2. If, instead, the four phenotypes in question 1
occur in approximately equal numbers, what are
the genotypes of the parents? What is this kind of
cross called?
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12.2 Later Modifications and Additions to
Mendel’s Principles
• Further research revealed many variations on
Mendel’s basic principles of dominant and
recessive inheritance:
•
•
•
•
•
•
Incomplete dominance
Codominance
Multiple alleles
Epistasis
Polygenic Inheritance
Pleiotropy
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Incomplete Dominance
• When one allele of a gene is not completely
dominant over another allele of the same gene, it
shows incomplete dominance
• The phenotype of the heterozygote is intermediate
between the phenotypes of the dominant and
recessive heterozygotes
• In a monohybrid cross, the phenotypes of F2
individuals are seen in a 1:2:1 ratio
• Example: Flower color in snapdragons
© 2017 Cengage Learning. All Rights Reserved.
Experimental Research: Incomplete Dominance
iStockphoto.com
The redflowered
snapdragon is
homozygous for
the
2. FC1 R allele.
iStockphoto.com
1. P
generation
X
Homozygous
Red C
red parent
R
R
C
W
White C
iStockphoto.com
generation
F1
C
offsprinPink
W
g all
pink
RC
WC
Homozygous
white
parent
The whiteflowered
snapdragon is
homozygous for
the
C W
allele.
Fusion of CR gametes from the red-flowered plant and
CW gametes from the white-flowered plant produces
CRCW heterozygotes in the F1. These plants have
pink flowers, an intermediate phenotype between red
and white. This phenotype is not that expected if
one of the alleles shows complete dominance to the
other allele. This phenotype is, however,
consistent with incomplete dominance.
© 2017 Cengage Learning. All Rights Reserved.
Experimental Research: Incomplete Dominance
(cont'd.)
3. Fl X Fl
cross
F1 pink-flowered plants are
crossed to produce the F2
generation.
X
Pink
R
4. F2
generation
C
W
Pink
C
R
Gametes from one
flowered plant
R
C
C
C
R
C
C
W
W
C
F1 pink-
W
R
C
Gametes from
another C RC W
F1 pinkflowered plant
C
C
R
C
R
C
R
C
W
Each parent plant produces two
types of gametes, C R and C W.
Random fusion of the gametes from
the two parents produces the F2
generation.
W
C
R
C
W
C
W
C
W
© 2017 Cengage Learning. All Rights Reserved.
Codominance
• Codominance occurs when the effects of two
alleles of a gene are equally detectable in
heterozygotes
• Example: Human MN blood group
• If the genotype is LMLM, the blood type is M
• If the genotype is LNLN, the blood type is N
• In heterozygotes – genotype LMLN – two
glycoprotein types are present, producing the blood
type MN
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Multiple Alleles
• Although an individual can have only two alleles
for a gene, multiple alleles (more than two
different alleles of a gene) may be present in the
population as a whole
• Example: Gene B may have several altered alleles
(b1, b2, b3, etc.), any two of which may be found in
an individual
• Multiple alleles of a gene each contain differences
at one or more points in their DNA sequences
© 2017 Cengage Learning. All Rights Reserved.
Multiple Alleles
B
allele
b1
allele
5'
3'
3'
5'
5'
3'
3'
5'
5'
3'
allele
3'
5'
b3
5'
3'
3'
5'
b2
allele
© 2017 Cengage Learning. All Rights Reserved.
ABO Blood Group
• The human ABO blood group is an example of
multiple alleles, dominance, and codominance
• Red blood cells from one blood type are
agglutinated (clumped) by an antibodies in the
serum of another type, sometimes causing fatal
transfusion reactions
• Example: People with type A blood have antigen A
on their red blood cells, and anti-B antibodies in
their blood – if they receive a type B transfusion,
the blood will clump
© 2017 Cengage Learning. All Rights Reserved.
Human Blood Types
© 2017 Cengage Learning. All Rights Reserved.
ABO Blood Group (cont'd.)
• The four blood types – A, B, AB, and O – are
produced by different combinations of multiple
(three) alleles of a single gene I designated IA, IB,
and i
• IA and IB are codominant alleles that are each
dominant to the recessive i allele
© 2017 Cengage Learning. All Rights Reserved.
Inheritance of Blood Types
Possible alleles in
gametes from father:
IA
A
or
IB
or
i
AB
A
IAIB
IAi
IA
IAIA
or
Possible
alleles
in gamete from
mother:
AB
B
IAIB
IBIB
A
B
B
IB
IBi
or
O
i
IAi
IBi
ii
© 2017 Cengage Learning. All Rights Reserved.
Epistasis
• In epistasis, two genes interact – alleles of a gene
at one locus inhibit or mask the effects of alleles of
a different gene at a different locus
• The result of epistasis is that some expected
phenotypes do not appear among offspring
• Epistasis is an important factor in determining an
individual’s susceptibility to common diseases
such as insulin resistance
© 2017 Cengage Learning. All Rights Reserved.
Epistasis in Labrador Retrievers
• The dominant B allele produces black fur color in
BB or Bb Labs – the recessive b allele produces
brown fur in bb Labs
• The dominant allele E of a second gene permits
pigment deposition – pigment deposition is
blocked in homozygous recessive ee individuals
• Epistasis by the E gene eliminates some of the
expected classes from crosses among Labs – BB
ee, Bb ee, and bb ee genotypes all have yellow fur
© 2017 Cengage Learning. All Rights Reserved.
Epistasis in Labradors
A. Black labrador
Erik Lam/Shutterstock.com
B. Chocolate
labrador
brown
c.byatt-norman/Shutterstock.com
C. Yellow labrador
c.byatt-norman/Shutterstock.com
© 2017 Cengage Learning. All Rights Reserved.
Homozygous parents:
Black
Yellow
Black
F1 puppies:
F2 offspring from cross of
two F1 Bb Ee dogs:
Gametes from one
Bb Ee F1 dog:
Gametes from
another Bb Ee
F1 dog:
F2 phenotypic ratio is 9 black : 3 chocolate : 4 yellow
Stepped Art
Polygenic Inheritance
• A continuous distribution of phenotypes (such as
height) typically results from polygenic
inheritance, in which several to many different
genes contribute to the same character
• These characters are known as quantitative
traits – individual genes that contribute to a
quantitative trait are known as quantitative trait
loci or QTLs
• When numbers of individuals in a series of defined
classes are plotted as a graph, polygenic
inheritance produces a bell-shaped curve
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Continuous Variation
A.
Students at Brigham Young University, arranged according to height
C. Idealized bell-shaped curve for a
population that displays continuous
variation in a trait
(Line of
bellshaped
curve
indicates
continuous
variation
in
population.
)
Number of individuals
in each height
category
Number of individuals
in each height
category
B. Actual distribution of individuals in
the photo according to height
1 4 8 1016 16 16 15 14 13 13 11 9 8 8 5 1 2
Shortest
heights
Range of
Tallest
Shortest
Range of heights
Tallest
If the sample in the photo included more
individuals, the distribution would more
closely approach this ideal.
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Polygenic Inheritance and the Environment
• Polygenic inheritance is often modified by the
environment
• Example: Height in humans is not the result of
genetics alone
• Poor nutrition during infancy and childhood limits
growth
• Good nutrition promotes growth
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Pleiotropy
• In pleiotropy, a single gene affects more than one
character of an organism
• Example: Sickle-cell anemia is caused by a
recessive allele of a single gene that alters
hemoglobin – wide-ranging pleiotropic effects
damage many tissues and organs in the body and
affect many body functions
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Pleiotropy in Sickle-Cell Anemia
Homozygous recessive individual
Abnormal hemoglobin
Sickling of red blood cells
Rapid destruction of
sickle cells leads to anemia
Impaired
mental
function
Clumping of cells and
interference with blood
circulation leads to local failures
in blood supply
Pneumonia
Heart failure
Heart failure
Kidney failure
Weakness
and fatigue
Abdominal
pain
Paralysis
STUDY BREAK 12.2
1. Palomino horses have a golden coat color, with a
white mane and tail. Palominos do not breed
true. Instead, there is a 50% chance that a foal
with two Palomino parents will be a Palomino.
What is the explanation?
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STUDY BREAK 12.2
2. A true-breeding rabbit with agouti (mottled,
grayish brown) fur crossed with a true-breeding
rabbit with chinchilla (silver) fur produces all
agouti offspring. A true-breeding chinchilla rabbit
crossed with a true-breeding Himalayan rabbit
(white fur with pigmented nose, ears, tail, and
leg) produces all chinchilla offspring. A truebreeding Himalayan rabbit crossed with a truebreeding albino rabbit produces all Himalayan
offspring. Explain the inheritance of the fur colors.
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