Transcript Pedigree Analysis

Pedigree Analysis
Key Words or Phrases
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Pedigree
Inheritance
Autosomal
Dominant
Recessive
Sex linked
Gene therapy
Biochemical testing
Viral vectors
Goals of Pedigree Analysis
• 1. Determine the mode of inheritance:
dominant, recessive, partial dominance,
sex-linked, autosomal.
• 2. Determine the probability of an affected
offspring for a given cross.
Basic Symbols
More Symbols
Mating
Offspring
Example of a Pedigree Chart
• A pedigree chart shows the incidence of a certain
condition as it goes through several generations
Types of Inherited Traits
• As you know, some traits are
dominant and some are
recessive.
• If you look closely at a
pedigree chart you may be
able to find clues about what
kind of inheritance it is
• For example, this chart shows
the incidence a recessive trait
Q: How do we know?
A: The first generation (I) do not
have affected parents yet one of
their offspring has the trait
Recessive Autosomal Pedigree
Autosomal Dominant
• Only one copy of the
gene will give someone
the condition
• All unaffected individuals
are homozygous for the
normal recessive allele.
• If one parent has the
condition, a child has a
50% chance of inheriting
it
Dominant Autosomal Pedigree
I
2
1
II
1
2
3
4
5
6
III
1
2
3
4
5
6
7
8
9
10
Dominant vs. Recessive
• Is it a dominant pedigree or a recessive pedigree?
• 1. If two affected people have an unaffected child, it must
be a dominant pedigree: D is the dominant mutant allele
and d is the recessive wild type allele. Both parents are
Dd and the normal child is dd.
• 2. If two unaffected people have an affected child, it is a
recessive pedigree: R is the dominant wild type allele
and r is the recessive mutant allele. Both parents are Rr
and the affected child is rr.
• 3. If every affected person has an affected parent it is a
dominant pedigree.
Sex-Linked Traits
• Most genes are on the
• Example of a Y
autosomal chromosomes
linked condition
(the first 22)
• But some may be on the
sex chromosomes
• If the affected gene is on
the Y chromosome, then
only men can get it
•
All direct male descendants will
inherit the condition
Sex – Linked Traits
• A sex linked trait may
also be on the X sex
chromosome
• If the trait is recessive,
men are still most likely to
inherit the condition
because women have
two copies of the gene
and men only have one
• So women are more likely
to get at least one copy of
the normal, dominant
gene
• Example of X linked
recessive trait
•
Not all men will inherit the
condition but men are more likely
to inherit the condition than
women
Sex-Linked Dominant
• Mothers pass their X’s to both
sons and daughters
• Fathers pass their X to
daughters only.
• Xd = recessive normal allele
• XD = dominant mutant allele
• If only the male has the trait
then all daughters would have
the condition but not the sons.
Genetic Testing
• Individuals at risk of inheriting Method
a genetic disorder may get
tested in different ways
Karyotype
What is
Analyzed
Example
Chromosome
number and sizes
Down Syndrome
Fluorescent
Hybridization
Fluorescent
image of
chromosome can
allow irregularities
to be seen
Chronic
Myelogenous
leukemia is a
translocation
disorder
Gene Testing
Sequence of DNA
bases on a gene
can show
mutations
Cystic Fibrosis
Biochemical
Testing
Testing for
proteins that are
indicative of a
disease
Tay Sachs
disease
Gene Therapy
• Gene therapy is a way of curing a genetic disease by inserting a
normal gene into the cells that are affected
• If scientists can obtain a normal copy of a mutated gene they can
put it inside a virus and inject the virus into an affected person
• Viruses can insert their DNA into the cells and allow the cells to
make a normal protein instead of a mutated one
• Still very new, gene therapy has
been used to treat certain types
of heart disease and immune
disorders