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?