Download Multiple Alleles, Sex-Linked Traits, Pedigrees

WHAT’S YOUR BLOOD T YPE?
A
B
AB
O
MULTIPLE ALLELES
Many genes have more than two alleles.
This does NOT mean that an individual
can HAVE more than two alleles.
This simply means that more than two
alleles for a trait exist in a population.
MULTIPLE ALLELES: EXAMPLE
Human blood type is controlled by multiple
alleles: A, B, O.
O is recessive, while A and B are codominant,
so if both alleles are present, both are
expressed.
There are four possible blood types: A, AB, B,
and O.
MULTIPLE ALLELES
WHAT HAPPENS IF WE GET THE WRONG
BLOOD FROM A BLOOD DONOR?
SEX-LINKED TRAITS AND CHROMOSOMES
 Autosomes are the “normal” or body chromosomes
 Sex chromosomes (X or Y) contain sex-linked genes
SEX-LINKED TRAITS AND CHROMOSOMES
 Specific pairs of these sex chromosomes are what
determine our sex. The genes on each chromosome
code for proteins that help us develop biologically
into males or females.
 Males have the sex chromosomes XY .
 Females have the chromosomes XX.
SEX-LINKED TRAITS
AND CHROMOSOMES
SEX-LINKED TRAITS AND CHROMOSOMES
 We get 1 X from mom, and either 1 X or 1 Y from
dad, so there is ALWAYS a 50-50 chance of being a
boy or girl. Which parent determines the gender of
the offspring?
 The dad.
X-LINKED TRAITS
AND DISORDERS
X-linked traits are
inherited through
genes on the
X chromosome.
X-LINKED TRAITS AND DISORDERS
X-linked disorders are more common in
males than in females. Why?
Males have only one X chromosome.
If the X chromosome carries a defective allele
for a gene, the Y chromosome does not have a
normal allele that is able to balance it out.
This results in a genetic disorder.
X-LINKED TRAITS
AND DISORDERS
If the X chromosome carries a
defective allele for a gene, the
Y chromosome does not have a
normal allele that is able to
balance it out.
X-LINKED TRAITS AND DISORDERS
 X-linked traits are usually passed down through the
mom. Why?
 Mothers can pass the genes
to daughters AND sons
 Fathers can pass genes to
daughters BUT NOT to sons
EXAMPLES OF X-LINKED DISORDERS
Colorblindness
 Decreased ability to see or distinguish between certain colors
 Red-green colorblindness, blue-yellow colorblindness
EXAMPLES OF X-LINKED DISORDERS
Colorblindness
 Decreased ability to see or distinguish between certain colors
 Red-green colorblindness, blue-yellow colorblindness
EXAMPLES OF X-LINKED DISORDERS
Hemophilia
 A bleeding disorder that prevents
blood from clotting properly
 The person bleeds more than
someone without hemophilia
EXAMPLES OF X-LINKED DISORDERS
Duchenne Muscular Dystrophy
 A disorder that involves rapidly
increasing muscle weakness and
loss of muscle tissue
BLOOD T YPE/MULTIPLE ALLELE
PRACTICE PROBLEMS…
PEDIGREES
A diagram that shows the inheritance pattern
of a trait over many generations is called a
pedigree.
HOW TO READ A PEDIGREE
Pedigree Symbols
I
Male Female
II
III
Marriage
Children/
Siblings
HOW TO READ A PEDIGREE
Looking at a family pedigree, we observe how
certain traits have been passed down from
parents to offspring and also how certain
traits and genetic disorders are expressed.
TIPS FOR INTERPRETING PEDIGREE
1 . How many males vs. females are af fected?
Equal = autosomal
More males = sex-linked
2. Does it skip generations?
Yes = recessive, No = dominant
3. Who is a carrier (unaf fected)?
females only = sex-linked
either sex = usually autosomal
AUTOSOMAL RECESSIVE INHERITANCE
1 . Males and females are equally af fected
2. May skip generations or appear to be an isolated event
3. Chance of of fspring having trait is ¼ if two parents are
heterozygous carriers
AUTOSOMAL DOMINANT INHERITANCE
1 . Males and females are equally af fected
2. Every af fected person has an af fected biological parent (no
skipping generations)
3. Normal siblings do not pass trait on to their of fspring
X-LINKED RECESSIVE INHERITANCE
1 . Males af fected more than females
2. May skip generations (ex. grandfather to grandson), but all
af fected males inherit trait from carrier mothers
3. The disease is never passed father to son – mothers are
carriers.
X-LINKED INHERITANCE: A CASE STUDY