As this disease is most commonly
prevalent in the elderly, some
members of the class may have
relatives with this disease so
please be a respectful and a
mature audience.
Alzheimer’s Disease
Lizzy Butler & Efe Osemeha
Period 3
Background Information
 Alzheimer’s Disease is a neurological disease that
kills neurons causing the loss of memory.
 Consists of 3 stages/levels: mild, moderate, severe
 Symptoms include: confusion, short attention
spans, and mood swings.
 Includes two abnormal
structures - plaques
and tangles
 Most common, Late-onset
form affects people over 60.

Most common
form associated
with apoE gene
on chromosome 19


Gene has 3 forms: 1 increases risk of
AD, other 2 helps protect against AD
Mutations in genes found on
chromosomes 1, 14, 21 cause rare
form of early-onset
 Early onset is
Mode of
Inheritance
inherited from an
Autosomal Dominant
Pattern
 Autosomal means that
it is not linked to the X
or Y chromosomes.
 Dominant means that
if one copy of the
allele is present, the
person will have the
 Specific sequence of nucleotides on DNA that
determine gene coding
 Can be variations in this sequence; each
variation is called an Allele
 Inherit one allele from each parent for each gene
 Dominant allele (R) determines outcome
regardless of the second allele, while recessive
allele (r) requires a match. Gene is represented
as combination (RR, Rr, rr)
 If sex-linked, represented as Xr, XR, or Y
Punnett Square
 In Punnett Squares: probability for child
to have genetic offspring determined by
parent's genes. (Represents Probability
per child)
 Female represented on left side; male
represented on top
A
a Aa
a Aa
a
aa
Heterozygous
dominant
aa
Homozygous
recessive
Homozygous
dominant
Probability Using Punnett Square

Ratios
(Must add up to 4 since there are 4 possible combinations)
homozygous dominant: heterozygous dominant: homozygous recessive
1
1 AA
:
2
2 Aa
:
1
1aa
• Percentages:
(Must equal to 100%)
homozygous dominant: heterozygous dominant: homozygous recessive
25%
50%
25%
25% AA
50% Aa
25%aa
Meaning of Letters

So what does Aa, aa, and AA mean?
If A represents the dominant allele Alzheimer’s and a represents
the recessive allele non- Alzheimer’s, then we can assume that:

Phenotype: (what is seen)




AA: Alzheimer's gene
Aa: Alzheimer’s gene (Non-Alzheimer’s gene carrier)
aa: Non-Alzheimer’s gene
Genotype: (what is in the genes)



AA: Homozygous Dominant (Alzheimer’s)
Aa: Heterozygous Recessive (Alzheimer's)
Aa: Homozygous Recessive (Non-Alzheimer’s)

Phenotype:
 Ratios: 3 Alzheimer's: 1 Non- Alzheimer’s
 Percentages: 75% Alzheimer’s: 25% NonAlzheimer’s

Genotype:
o Ratios: 1AA: 2Aa: 1aa
o Percentages:
25% AA : 50% Aa : 25% aa
Student Practice with Punnett Square
Father’s Genes
Mother’s Genes
A
a
a
Aa
Aa
a
aa
aa
• If an heterozygous Alzheimer’s
father marries a homozygous nonAlzheimer’s mother, use a Punnett
square to illustrate the probability of
a child developing Alzheimer’s.
• Genotype:
– Ratio: 2 AD, 2 non-AD
– Percentage: 50% AD - 50% non
AD
• Phenotype:
– Ratio: 2 Aa : 2 aa
– Percentage: 50% Aa : 50% aa
3 Generation Hypothetical Pedigree
I
II
III
• Circle- female
Square- male
– All white- homozygous recessive gene (has 2 copies of “healthy” gene)
– All green- homozygous dominant (has AD, 2 copies of “bad” gene)
– Half green/half white- heterozygous (person has AD, one healthy, one bad)
•
Student Practice
I
Key:
– Circle: female
– Square: male
– Shaded in:
Alzheimer’s
– Not shaded in: nonAlzheimer’s
– Half shaded in:
Dominant,
Alzheimer’s
II
III
• How do we know that neither of Generation I are homozygous dominant?
• Is it possible for the middle daughter of Generation II to have an offspring that
does not suffer from Alzheimer’s?
• Is there any chance that offspring of the first daughter in Generation II develops
Alzheimer’s?