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

Mode of Inheritance

Early onset is 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 disease.

Inheritance of Late onset is uncertain Environmental factors

such as chosen lifestyles may play a factor.

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

a Aa aa

a Aa aa Homozygous recessive

Heterozygous dominant

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 : 2 : 1 1 AA 2 Aa 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% Non-

Alzheimer’s

Genotype:o Ratios: 1AA: 2Aa: 1aao Percentages:

25% AA : 50% Aa : 25% aa

Student Practice with Punnett Square

• If an heterozygous Alzheimer’s father marries a homozygous non-Alzheimer’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

A a

a

a

Aa

Moth

er’

s G

en

es

Father’s Genes

Aa aa

aa

3 Generation Hypothetical Pedigree

• 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)

I

II

III

Student Practice

• 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?

I

II

III

• Key:– Circle: female– Square: male– Shaded in:

Alzheimer’s– Not shaded in:

non- Alzheimer’s

– Half shaded in: Dominant, Alzheimer’s