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Human Genetics: concepts and applications
6th edition
Ricki Lewis
Chapter 4
Mendelian Inheritance
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Congential insensitivity to pain (OMIM
256800)
• Cannot sweat,
retardation, don’t
feel pain
Severe burns on finger tips from holding a
radiator and extensive lacerations of tongue with
loss of the tip.
4-2
Ch 4
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Acrocephalosyndactyly (OMIM 105200)
• Large toes
because they
have double
bones in each toe
4-3
Ch 4
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Ataxia Telangiectasia (AT) (OMIM 208900)
4-4
• Defect in a kinase that
functions as a cell cycle
checkpoint. Cell
proceed through the cell
cycle without pausing
just after replication to
inspect the new DNA
and to repair any
mispaired bases.
• Autosomal recessive
• Racial rash, poor
muscular coordination,
involuntary eye
movements, high risk
for cancer, sinus and
lung infections.
Ch 4
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Batten Disease (OMIM 204500)
Natalie E. Aurelio
In the arms of her loving parents and
brother, Natalie passed away
peacefully with a beam of warm
sunshine on her face August 28, 2004.
Born June 24, 1990, in Los Gatos,
Natalie’s life was brief but with her
gentle smile, radiant eyes and
boundless courage, she inspired
countless friends and strangers alike.
4-5
• Autosomal recessive
• Lack of a lysosomal
enzyme causes
lipofuision to build up
in brain cells.
• Jerky movement, poor
coordination, seizures,
visual loss,
developmental delay
• There are currently
about 2000 children
diagnosed with Batten
Disease in the US
alone and many others
yet undiagnosed
Ch 4
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Cystic fibrosis CF (OMIM 219700)
4-6
• Autosomal recessive
• The thick, sticky
mucus that clogs
airways must be
coughed up at least
twice every day.
• CFTR protein
remains in the
cytoplasm, rather
than anchoring in
the plasma
membrane. This
prevents normal
chloride channel
function.
• Lung infections and
congestion, poor fat
digestion, male
infertility, poor
weight gain, salty
sweat
Ch 4
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Familial hypertrophic cardiomyopathy
(OMIM 192600)
• Autosomal
recessive
• Overgrowth of
heart muscle,
causing sudden
death in young
adults.
4-7
Ch 4
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Gaucher disease (OMIM 230800)
• Autosomal
recessive
• Swollen liver and
spleen, anemia,
internal bleeding,
poor balance.
4-8
Ch 4
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Hemochromatosis (OMIM 235200)
4-9
The dark reddish brown color of liver
surface is characteristic in
hemochromatosis. The liver surface of this
case shows granular change, suggesting
the presence of a fine nodular formation in
liver histology
• Autosomal
recessive
• Iron retention;
high risk of
infection,liver
damage, excess
skin
pigmentation,
heart and
pancreas damage
Ch 4
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Maple Syrup urine disease(OMIM 248600)
• Autosomal recessive
• Can not digest 3 types of
amino acids.
• This disease presents very
dramatic signs in the
newborn period such as poor
feeding, lethargy,
convulsions, and even death,
occurring within the first few
days of life.
• Dietary restrictions must be
maintained through the
lifetime of an affected
individual.
• The disease derives its name
from the sweet, burnt sugar,
or maple syrup smell of the
urine
4-10
Ch 4
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Phenylketonuria PKU (OMIM 261600)
4-11
• Autosomal
recessive
• Unable to
breakdown
phenyalanine
• Mental
retardation
• Fair skin
• Test at birth
• Special diet
Ch 4
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Sickle Cell anemia (OMIM 603903)
4-12
Normal red blood cells and a sickled cell.
Sickle cell anemia is an inherited blood
disease. In normal red blood cells,
hemoglobin carries oxygen from the
lungs to organs and tissues and brings
back carbon dioxide to the lungs. In
sickle cell anemia hemoglobin is
defective. After carrying oxygen to organs
and tissues some may cluster together
and form rod-like structures causing the
red blood cell to become stiff and to form
the sickle shape.
Ch 4
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Sickle Cell anemia (OMIM 603903)
Autosomal recessive
Normal red blood cells and a sickled cell. Sickle cell anemia is an inherited blood disease. In
normal red blood cells, hemoglobin carries oxygen from the lungs to organs and tissues and
brings back carbon dioxide to the lungs. In sickle cell anemia hemoglobin is defective. After
carrying oxygen to organs and tissues some may cluster together and form rod-like structures
causing the red blood cell to become stiff and to form the sickle shape.
4-13
Ch 4
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Tay-Sachs disease (OMIM 272800)
Molly Grace was born on September
26,2003. She was born 2 months early
and weighed only 4lbs.
At 18 months we received the
devastating news. My beautiful perfect
baby had a rare degenerative disease
4-14
called Tay-Sachs.
• Autosomal
recessive
• Lysosome enzyme
is absent – it
normally breaks
down lipid
• Lose skills at 6
months, then sight
and hearing,
movement
• Die by 3 years
Ch 4
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Achondroplasia (OMIM 100800)
• Autosomal
dominant
• Dwarfism with
short limbs,
normal-size head
and trunk
4-15
Ch 4
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Familial hypercholesterolemia (FH) (OMIM
144010)
• Autosomal dominant
• High Cholesterol
• The photograph shows
cholesterol deposits on the
elbow of an affected young
man.
• A heterozygous has half the
normal number of cell surface
receptors in the liver for LDL
cholesterol.
• An individual with two mutant
alleles has the severe form of
FH, with liver cells that totally
lack the receptors. Serum
cholesterol level is very high
4-16
Ch 4
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Huntington Disease (OMIM 143100)
• Autosomal
dominant
• Progressive
uncontrollable
movements and
personality
change,
beginning in
middle age
4-17
Ch 4
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Lactose Intolerance (OMIM 150200)
•
•
•
•
•
4-18
Autosomal dominant
Lack enzyme that breaks down
lactose
When someone says he or she
is "lactose intolerant" that
means the inability to digest a
milk sugar (or carbohydrate)
called lactose.
Although this might not seem
like a big deal, think about how
many different kinds of foods
you eat each day that contain
milk - maybe it's in your coffee,
yogurt, or the cream cheese
you spread on a bagel.
Between 30 to 50 million
Americans are lactose
intolerant and certain ethnic
populations are more widely
affected than others.
Ch 4
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Marfan Syndrome (OMIM 154700)
•
•
•
•
•
•
•
•
4-19
Autosomal dominant
Flo Hyman was a 6’5” star on
the U.S. women’s volleyball
team that won a silver medal
in the 1984 Olympics. Two
years later, at the age of 31,
she died in a volley ball game
from a ruptured aorta caused
by Marfan Syndrome.
The gene responsible for
Marfan Syndrome is located on
chromosome 15.
The normal gene codes for
fibrillin, which is part of
connective tissue.
1 in 10,000 individuals
It has been suggested that
Abraham Lincoln had Marfan.
Long limbs, sucken chest, lens
dislocation, spindly fingers,
weakened aorta
pleiotropy
Ch 4
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Myotonic dystrophy (OMIM 160900)
• Autosomal dominant
• Progressive muscle
wasting
• The facial appearance
just about clinches the
diagnosis, it is
so characteristic. The
lids droop, often with a
bit of misconvergence
and wandering of the
eyes
4-20
Ch 4
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Neurofibromatosis type 1 (NF1) (OMIM 162200)
4-21
• Autosomal dominant
• Defective signal
transduction – tumors
grow in nervous tissue –
fails to block
transmission of growth
factor – cells divided
inappropriately.
• Clinical manifestations
of NF1 (1). The images
show café-au-lait spots,
freckling, neurofibromas
and iris Lisch nodules.
Scoliosis,
pseudarthrosis, bowing,
optic pathway glioma,
Plexiform
neurofibromas
Ch 4
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Polycystic Kidney disease (OMIM 173900)
4-22
• Autosomal
dominant
• Cysts in
kidney’s, bloody
urine, high blood
pressure.
Abdominal pain
• It affects 1 in 500
individuals.
Ch 4
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Polydactyly (OMIM 174200)
• Autosomal
dominant
• Polydactyly –
extra fingers
and or toes – is
a Mendelian
trait,
determined by a
single gene.
4-23
Ch 4
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4-24
A child inherits half of his or her genes from each parent. It is
interesting to observe how traits reasort with each generation
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Inheritance
• Parents and offspring
often share observable
traits.
• Grandparents and
grandchildren may share
traits not seen in parents.
• Why do traits disappear
in one generation and
reappear in another?
4-25
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Facial similarities are not always as obvious as those between
Rocker Steven Tyler of Aerosmith and his actress daughter,
LIV.
4-26 Liv’s son Milo inherited her family’s famous facial features.
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Gregor Mendel
father of modern genetics
Combined
• Plant breeding
• Statistics
• Careful
recordkeeping
Described hypothesis of transmission of traits
now considered laws of inheritance
Mendel followed the inheritance of traits through several
4-27Generations in pea plants.
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4-28
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4-29
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Mendel studied pea traits
with two distinct forms
Gregor Mendel studied the transmission of seven traits in pea
Plants. Each trait has two easily distinguished expressions, or
4-30
Phenotypes. Mendel’s characters are genes.
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True breeding plants
Plants which
consistently have
offspring with same
trait as parent are true
breeding plants.
The second generation
Resulting from a genetic cross
Is the F1 generation.
4-31
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Original or parental cross
of two homozygotes
• What happens
when true breeding
plants with two
distinct forms of a
trait are crossed?
Progeny show only one form
of the trait.
The observed trait is called dominant.
The masked trait is called recessive.
In pea plants, the allele for tall (T) is dominant to the allele
4-32 For short (t). The genotype for a short pea plant is tt.
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Test cross
Is a plant showing the dominant trait true-breeding or not?
Test by crossing with a plant showing the recessive trait.
4-33
All tall offspring indicate
parent is true-breeding
Mixed offspring indicate
parent is hybrid
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Crossing monohybrids to each other
Hybrid parents show the
dominant trait (tall).
Offspring:
• Dominant trait (tall) and
true breeding (1/4 total)
• Dominant trait (tall) and
NOT true breeding (1/2 total)
• Recessive trait (short) and
always true breeding
(1/4 total)
Mendel concluded that among the hybrid parents the
short trait (recessive) was hidden but not absent
4-34
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Mendel’s data
1. Crossed true-breeding plants differing at one of seven traits.
2. Crossed hybrid offspring to each other (all show dominant trait).
3. Counted offspring of hybrid crosses.
Offspring
Seed form
7,324
5,474
1,850
2.96 : 1
Seed color
8,023
6,022
2,001
3.01 : 1
929
705
224
3.15 : 1
Pod form
1,181
882
299
2.95 : 1
Pod color
580
428
152
2.82 : 1
Flower position
858
651
207
3.14 : 1
1,064
787
277
2.84 : 1
Trait
Seed coat color
Stem length
4-35
Ratio
# with
dominant :
recessive trait recessive
# with
dominant
trait
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04_01.jpg
Mendel called physical units responsible for the inheritance of
Traits “characters.” The basis for his first law is that characters
Separate from each other during meiosis.
4-36
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Law of segregation
Why do traits “disappear” in one generation only
to reappear in a subsequent generation?
• Each plant possesses two distinct separable
units (alleles) for each trait inherited from
each parent.
• Gametes contain ONE allele for each trait.
• Only one version is observed in an individual.
The unit (allele) does not disappear.
It may be present but hidden.
4-37
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Law of segregation
During meiosis, homologous pairs of chromosomes (and the genes
That compose them) separate from on another and are packaged
Into separate gametes. At fertilization, games combine at random
To
4-38form the individuals of a new generation. Green and blue denote
Different parental origins of the chromosomes.
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Alleles
Mendel’s units (or “elementen”) are called alleles
(genes).
• Versions of the same gene or DNA sequence.
• Differ in DNA sequence at one or more sites.
Alleles are alternate forms of a single gene.
4-39
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Genotype
indicates the combination of alleles present
•
Homozygous alleles are the same
•
Heterozygous alleles differ
When Mendel crossed pure breeding peas having yellow seed color
(YY) with pure breeding peas having green seed color (yy), all of the
offspring had yellow seed color. The symbols YY and yy represent
genotypes.
Phenotype
indicates the trait observed.
When Mendel crossed pure breeding peas having yellow seed color
(YY) with pure breeding peas having green seed color (yy), all the
offspring had yellow seed color. Yellow seed color represents the
phenotype.
4-40
Terms distinguish the observed form
and the underlying alleles present.
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Genotype and phenotype
Phenotype
Genotype
Tall plant
Homozygous dominant
“tall-associated” alleles
TT
Heterozygous
Tt
Homozygous recessive
“short-associated” alleles
tt
Short plant
4-41
Abbreviation
of genotype
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Modern terms for Mendel’s crosses
• Mendel’s true-breeding plants were
homozygous for the alleles of a trait.
A person who has two identical
alleles for a particular gene is
Homozygous for that gene.
• Mendel’s hybrids were heterozygous
for the alleles of a trait.
A heterozygote for a particular
gene has 2 variants of the
Gene.
4-42
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Wildtype
most common version in the general population
• wildtype phenotype
•
most common phenotype
• mutant phenotype
•
phenotype different from
the wildtype
• wildtype allele
•
most frequent allele
associated with the
common phenotype
• mutant allele
• allele associated with the
mutant phenotype.
4-43
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Law of segregation: the monohybrid
cross
Tt x Tt is a monohybrid
Cross.
A monohybrid cross yields a
Genotypic ratio of 1:2:1 and
A phenotypic ratio of 3:1.
Two heterozygous parents produce gametes
with T or t allele equally frequently.
Offspring genotypes 1/4 TT : 1/2 Tt : 1/4 tt
Offspring phenotypes
4-44
3/4 tall
: 1/4 short
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A Punnett square is a diagram of how two alleles of a gene
combine in a cross between two individuals. The different
types of gametes of one parent are listed along the top of the
square, with those of the other parent listed on the left-hand
side. Each compartment within the square contains the
genotype that results when gametes that correspond to that
compartment join. The Punnett square here describes a
monohybrid cross of two tall pea plants. Among the progeny,
4-45
tall plants outnumber short plant 3:1.
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Mode of inheritance
indicates the patterns with which the mutant
phenotype is associated.
Autosomal recessive
Autosomal dominant
X-linked recessive
X-linked dominant
Y-linked
mitochondrial
4-46
Most common
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Autosomal dominant inheritance
• Heterozygotes exhibit
the affected phenotype.
• Males and females are
equally affected and
may transmit the trait.
• Affected phenotype
does not skip
generation.
4-47
An autosomal dominant
Trait can affect either sex.
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Autosomal dominant inheritance. When one parent has an
autosomal dominant condition and the other does not, each
offspring has a 50 percent probability of inheriting the mutant
allele and the condition. The affected parent is Aa here, and not
AA, because for many dominant disorders, the homozygous
dominant AA phenotype is either lethal or rare because both
parents of the person with the AA genotype would have to
have the disorder.
4-48
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Autosomal recessive inheritance
• Heterozygotes carry
the recessive allele
but exhibit the
wildtype phenotype.
• Males and females are
equally affected and
may transmit the trait.
• May skip generations.
A 1:2:1 genotypic ratio results from a monohybrid cross,
whether in peas or people. Curly hair (C) is dominant
4-49 to straight hair (c). This pedigree depicts a monohybrid cross
for hair curliness.
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• The probability that a child in a particular
family will inherit a recessive disorder is
¼. If the parents have four children, what
is the probability that their third child will
inherit the disorder? ¼
• A man and his wife are both carriers of the
recessive allele causing Tay-Sachs
disease (chromosome 150. If they have a
normal child, what is the probability that
the child is a carrier of Tay Sachs? 2/3
4-50
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Comparison of autosomal dominant
and autosomal recessive inheritance
Autosomal Autosomal
dominant recessive
4-51
Males and females
affected?
Yes
Yes
Males and females
transmit the trait?
Yes
Yes
Trait skips generations?
No
Yes
At least one parent of
affected child must be
affected?
Yes
No
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04_03.jpg
4-52
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4-53
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Law of independent assortment
• Two genes on different chromosomes
segregate their alleles independently.
• The inheritance of an allele of one gene
does not influence which allele is
inherited at a second gene locus.
4-54
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4-55
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4-56
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4-57
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4-58
Online Mendelian Inheritance in Man (OMIM) is the most
Comprehensive list of human traits and genetic diseases.
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Law of independent assortment
4-59
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Law of independent assortment
• The independent assortment of genes carried on
different chromosomes results from the random
alignment of chromosome pairs during metaphase of
meiosis I. An individual of genotype RrYy, for
example, manufactures four types of gametes,
containing the dominant alleles of both genes (RY),
the recessive alleles of both genes (ry), and a
dominant allele of one with a recessive allele of the
other (Ry or rY). The allele combination depends
upon which chromosomes are packaged together in
a gamete – and this happens at random.
4-60
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Independent assortment of two traits
• In a dihybrid cross, parents with two
differing traits are crossed.
• Which allele is dominant?
Heterozygous peas are round and yellow.
Therefore
4-61
round is dominant to wrinkled
yellow is dominant to green
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Two traits segregating independently
The genotypic ratio
Expected from a
Dihybrid cross is
9:3:3:1.
A Punnett square can represent the random combinations of
gametes produced by dihybrid individuals. An underline in a
genotype (in the f2 generation) indicates that either a dominant
or recessive allele is possible. The numbers in the F2 generation
4-62
are Mendel’s experimental data.
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• A man and a woman are both carriers
for two autosomal recessive
disorders, PKU (chromosome 12)
and cystic fibrosis (chromosome 7).
If they have a daughter, what is the
probability that she will have PKU
but not CF? 3/16
4-63
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Two traits segregating independently
315 round yellow peas
423
108 round green peas
416
101 wrinkled yellow peas
140
133
32 wrinkled green peas
3.18
4-64
:
1
2.97 :1
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Probability
The likelihood that an event will occur.
•No chance of event
probability = 0
(e.g. chance of rolling 8 on a six-sided die)
•Event always occurs probability = 1
(chance of rolling 1,2,3,4,5,or 6 on a six-sided die)
The probabilities of all the possible events add up to 1.
4-65
# on die
probability
1
1/6
2
1/6
3
1/6
4
1/6
5
1/6
6
1/6
The probability of an event
= # of chance of event
total possible events
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Independent events
The probability of independent events is calculated
by multiplying the probability of each event.
In two rolls of a die, the chance of rolling the number 3 twice:
Probability of rolling 3 with the first die
= 1/6
Probability of rolling 3 with the second die = 1/6
Probability of rolling 3 twice = 1/6 x 1/6 or 1/36
4-66
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Dependent events
The probability of dependent events is calculated
by adding the probability of each event.
In one roll of a die, what is the probability of rolling either
the number 5 or an even number?
Probability of rolling the number 5
= 1/6
Probability of rolling an even number = 3/6
Probability of rolling 5 or an even number = 1/6 + 3/6 or 4/6
4-67
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Independent events
What is the chance of an
offspring having the
homozygous recessive
genotype when both parents
are doubly heterozygous?
Using the product rule, the
Probability that parents
Heterozygous for two traits
(AaBb) will produce a
Homozygous recessive
Offspring (aabb) would be?
1/16
4-68
The product rule.
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Dependent events
Parents are heterozygous for a trait, R.
What is the chance that their child is carries
at least one dominant R allele?
Probability of child carrying RR = 1/4
Probability of child carrying Rr = 1/2
Probability of child carrying R_ = 1/4 + 1/2 = 3/4
4-69
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• An Amish couple (both normal) has four
children. The first three children are
normal and the fourth child was born with
an autosomal recessive disorder known
as Ellis-van Creveld sysndrome (EvC).
EvC was once referred to as ‘six-fingered
dwarfism’ and is caused by a defective
gene on chromosome 4. What is the
probability that their next child will have
Ellis-van Creveld syndrome? ¼
• The Amish couple in the previous
question has a fifth child born with PKU.
What is the probability that their sixth
child will have both PKU and EvC? 1/16
4-70
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• What is the probability that two
heterozygous individuals (Hh) will
produce a homozygous recessive
offspring? ¼
• For two traits A and B, what are the
genotypes of the gametes that a
heteozygous would produce? AB,
Ab, aB, ab
4-71
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• For pea plants, yellow seed color (Y) is
dominant to green seed color (y). In one
experiment, a cross produced 6,022 plants
with yellow seed color and 2,001 plants
with green seed color. Describe the
genotype of a plant with green seed color?
yy
• Describe the genotype of the plant with
yellow seed color? Cannot be determined
by looking at it.
4-72
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• Sickle cell anemia is inherited as an
autosomal recessive trait. Describe the
genotype of an unaffected individual who
has a sibling with sickle cell anemia?
Cannot be determined by the phenotype.
• Describe the genotype of an individual
with sickle cell anemia? Homozygous
recessive
• In a pedigree analysis, you should expect
the trait to skip generations.
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• James Poush, discovered distal
symphalangism in his family and
published a report on his findings.
This condition is inherited as an
autosomal dominant trait. Describe a
person with this condition.
Homozygous dominant or
heterozygous dominant
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• Distal symphalangism is inherited as an
autosomal dominant trait. The condition
causes stiff fingers and toes that have tiny
nails. Describe an unaffected person who
has two parents with this condition.
Homozygous recessive
• In a pedigree, you would expect this trait
to occur in every generation.
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Pedigrees
symbolic representations of family relationships
and inheritance of a trait
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• In a human pedigree that traces the
inheritance of sickle cell disease, a
half-filled circle represents a
heterozygous female.
• In a pedigree, autosomal recessive
traits tend to skip generations.
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Autosomal dominant inheritance of brachydactyly
Heterozygotes exhibit the phenotype.
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A paritial
Pedigree of
Egypt’s
Ptolemy
Dynasty
shows only
genealogy,
not traits. It
appears
almost
ladderlike
because of
the extensive
Inbreeding. From 323 B.C. to Cleoparta’s death in 30 B.C.. The
family experienced one pairing between cousins related through
half-brothers. (generation III), four brother-sister pairings (IV,VIII,
and
4-79 X), and an uncle-niece relationship. Cleopatra married her
Brother, Ptolemy XIII, when he was 10 years old.
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The Egyption pedigree, a family with polydactyly (extra fingers
And toes) extends laterally, with many children.
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The most common form of consanguinity is marriage of first
cousins. The share one set of grandparents, and therefore risk
passing on the same recessive alleles to offspring.
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Autosomal recessive inheritance of albinism
Heterozygotes carry the recessive allele
but exhibit the wildtype phenotype
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Albinism affects males and females and can skin generations,
as it does here in generations I and II the homozygous recessive
individual lacks an enzyme needed to produce melanin,
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which colors the eyes, skin, and hair.
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A pedigree for an autosomal dominant trait. Autosomal dominant
traits do not skip generations. This trait is brachydactyly, or
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short fingers.
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A inconclusive pedigree. This pedigree could account for an
autosomal dominant trait or an autosomal recessive trail or an
autosomal recessive trait that does not prevent affected
individuals from having children. (Unfilled symbols could be
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carriers.
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Genetic predictions
Ellen’s brother Michael has
sickle cell anemia, an
autosomal recessive
disease.
Ellen and Michael’s parents
must be carriers.
What is the probability that
Ellen’s child has a sickle cell
anemia allele (a)?
Ellen is not affected and
cannot carry aa genotype
chance Ellen is a carrier = 2/3
chance child inherits sickle
cell allele = 1/2
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Overall chance child carries
sickle cell allele from Ellen =
2/3 x 1/2 = 1/3
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04_18a.jpg
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04_18b.jpg
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04_18c.jpg
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Below are four pedigrees depicting families with achondroplasia,
A common form of hereditary dwarfism that causes very short
Limbs, stubby hands, and an enlarged forehead. What is the
Most likely mode of inheritance?
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Chands syndrome is an autosomal recessive condition
characterized by very curly hair, underdeveloped nails, and
abnormally shaped eyelids. In the following pedigree,
which individuals must be carriers?
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Congenital insensitivity to pain with anhidrosis is an extremely rare
autosomal recessive condition that causes fever, inability to sweat,
mental retardation, inability to feel pain, and self-mutilating
behavior. Researchers compared the following three families with
this condition. What do these families have in common that
might explain the appearance of this rare illness?
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In this pedigree, individual III-1 died at age two of Tay-Sachs
disease., as autosomal recessive disorder. Which other family
members must be carriers, and which could be?
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According to this pedigree from the soap opera “All My Children”
is Charlie the product of a consanguineous relationship? The
trait being studied is freckles.
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On “General Hospital,” six-year-old Maxi suffered from Kawasaki
Syndrome, an inflammation of the heart. She desperately needed
A transplant, and received one from BJ, who died in a bus
Accident, Maxi and BJ had the same unusual blood type, which
Is inherited. According to this pedigree, how are Maxi and BJ
Related?
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