Download Pedigree

DOMINANT AND RECESSIVE
TRAITS
ATTACHED / UNATTACHED EARLOBES
UNATTACHED
DOMINANT
ATTACHED
RECESSIVE
ROLLING YOUR TONGUE
ROLLER
DOMINANT
NONROLLER
RECESSIVE
WIDOW’S PEAK
WIDOW’S PEAK
DOMINANT
STRAIGHT HAIRLINE
RECESSIVE
HITCHHIKER’S THUMB
STRAIGHT THUMB
DOMINANT
HITCHHIKER’S THUMB
RECESSIVE
PINKIES
BENT PINKIES
DOMINANT
STRAIGHT PINKIES
RECESSIVE
CLEFT CHIN
NO CLEFT
DOMINANT
CLEFT
RECESSIVE
SECOND TOES
LONGER SECOND TOE
DOMINANT
SHORTER SECOND TOE
RECESSIVE
NUMBER OF FINGERS
SIX FINGERS:
POLYDACTYLY
FIVE FINGERS
DOMINANT!!!!
RECESSIVE
Section Objectives:
• Interpret a pedigree.
• Identify human genetic disorders caused by
inherited recessive alleles.
• Predict how a human trait can be determined
by a simple dominant allele.
• A family tree traces a family name and various family
members through successive generations.
• Through a family tree, you can identify the
relationships among your cousins, aunts, uncles,
grandparents, and great-grandparents.
• A pedigree is a graphic representation of genetic
inheritance.
• It is a diagram made up of a set of symbols that
identify males and females, individuals affected by the
trait being studied, and family relationships.
• Basically, a family tree that traces an inherited trait.
Male
Parents
Female
Siblings
Affected
male
Affected
female
Mating
Known
heterozygotes
for recessive
allele
Death
Some
pedigree
symbols
I
1
2
II
3
2
1
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• Highlighted circles
and squares
represent individuals
showing the trait
being studied.
I
1
2
II
2
1
3
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• Circles and
squares that are
not highlighted
designate
individuals that do
not show the trait.
• A half-shaded circle or
square represents a
carrier, a heterozygous
individual.
I
1
2
II
2
1
III
?
IV
1
2
1
3
4
4
3
2
5
3
4
5
• A horizontal line
connecting a circle
and a square
indicates that the
individuals are
parents, and a vertical
line connects parents
with their offspring.
I
1
2
II
1
III
1
?
IV
2
1
3
2
4
4
3
2
5
3
4
5
• Each horizontal row
of circles and
squares in a pedigree
designates a
generation, with the
most recent
generation shown at
the bottom.
I
1
2
II
1
3
2
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• The generations are
identified in
sequence by Roman
numerals, and each
individual is given an
Arabic number.
Simple Recessive Heredity
• Most genetic disorders are caused by recessive
alleles.
Bb
x
bb
Bb
Bb
x
bb
bb
Cystic Fibrosis
• Cystic fibrosis (CF) is one of the most
common fatal genetic disorders among mostly
white Americans.
• Due to a defective protein in the plasma
membrane, cystic fibrosis results in the
formation and accumulation of thick mucus in
the lungs and digestive tract.
• Approximately one in 28 white Americans carries the
recessive allele, and 1 in 3000 children born to white
Americans inherits the disorder. (1 in every 15,000
black babies are born with the disease every year)
Tay-Sachs
• Tay-Sachs (tay saks) disease is a fatal
recessive disorder of the central nervous
system.
• In this disorder, a recessive allele results in the
absence of an enzyme that normally breaks
down a lipid produced and stored in tissues of
the central nervous system.
• Because this lipid fails to break down properly,
it accumulates in the cells.
Tay-Sachs
• A baby born with Tay-Sachs usually seems
healthy for the first few months, but as nerve
cells become packed down with fatty material
a relentless deterioration of mental and
physical abilities begins to occur.
• Tay-Sachs is very rare, and more commonly
found in families with Jewish heritage and
Cajun-French families.
What’s
wrong
with this
Tay-sachs
pedigree?
I
1
2
II
1
2
3
4
1
2
III
3
IV
1
Phenylketonuria
• Phenylketonuria (fenal key ton Your ree uh), also
called (PKU), is a recessive disorder that results
from the absence of an enzyme that breaks down
the amino acid, phenylalanine.
• Because phenylalanine cannot be broken down, it and
its by-products accumulate in the body and result in
severe damage to the central nervous system.
Phenylketonuria
• Affects around 1 in every 15,000 births. Usually
found mostly in Caucasian and Asian families
• Infants affected by PKU are given a diet that is
low in phenylalanine until their brains are fully
developed.
Phenylketonuria
Contains Phenylalanine
Simple Dominant Heredity
• Many traits are inherited just as the rule of
dominance predicts.
• Remember that in Mendelian inheritance, a
single dominant allele inherited from one
parent is all that is needed for a person to
show the dominant trait.
Simple dominant traits
• A cleft chin, widow’s
peak hairline, almond
shaped eyes, thick
lips, and the presence
of hair on the middle
section of your fingers
all are examples of
dominant traits.
Huntington’s Disease
• Huntington’s disease is a lethal genetic
disorder caused by a rare dominant allele.
• It results in a breakdown of certain areas of
the brain. Causing gradual involuntary
muscle movements and eventually
dementia.
Huntington’s Disease
• Ordinarily, a dominant allele with such severe
effects would result in death before the
affected individual could have children and
pass the allele on to the next generation.
• But because the onset of Huntington’s disease
usually occurs between the ages of 30 and 50,
an individual may already have had children
before knowing whether he or she is affected.
Typical Pedigree of Huntington’s Disease
I
1
2
II
2
1
4
3
5
III
1
2
3
4
5
Question
1
I
1
2
What does this
pedigree tell you
about those who
show the recessive
phenotype for the
disease?
II
1
2
3
4
1
2
III
3
IV
1
I
1
The pedigree
indicates that
showing the
recessive
phenotype for the
disease is fatal.
2
II
1
2
3
4
1
2
III
3
IV
1
Question 2
What must happen for a person to show a recessive
phenotype?
Answer
The person must inherit a recessive allele for
the trait from both parents.
Question 3
Which of the following diseases is the result of a
dominant allele?
A. Huntington’s disease
B. Tay-Sachs disease
C. cystic fibrosis
D. phenylketonuria
The answer is A.
Question 2
If T is the allele for tall plants and t is the allele for
short plants, the phenotype of individual 4 is _______.
T
t
T
1
2
t
3
4
The answer is short. Recall that phenotype
describes the way an organism looks.
T
t
T
1
2
t
3
4
Question 3
The genotype of individual 1 is _______.
T
t
T
1
2
t
3
4
The answer is TT. The allele combination
that an organism contains is its genotype.
T
t
T
1
2
t
3
4