• Principle of segregation: genes remain intact and distinct. They segregate during meiosis and are transmitted as distinct entities.
• Principle of Independent assortment: genes at different loci are transmitted independently.

Refers to the different forms of of DNA sequences that a gene has in a population

Individuals allelic constitution at a locus.

Aa AA aa

The same genotype producing different phenotypes in different environments.

Monogenic Inheritance

• Assumes single gene defect.
• Usually follows Mendelian Pedigree

• Males and Females transmit the trait with equal frequency.
• Successive generations are affected. (no generations skipped)

• Huntington's
• Myotonic Dystrophy
• Marfan syndrome

• Sickle cell anemia
• Cystic fibrosis
• MODY(maturity onset diabetes of the young)- mutation in glucokinase gene.
• Phenylketonuria- mutation in phenylalanine hydroxylase.

• Notable for their expression in males
• Males always display disease when they inherit mutated gene.
• X-linked dominant and recessive genes are only applicable in females
• Fathers can't pass it on to their sons, but daughters must inherit trait.

• Affected males always express trait.
• Affected females have an affected father and a mother who is either affected or a carrier.
• Can skip a generation
• Sons must get it from their mother

• Sometimes happens with X-Linked Inheritance.
• The father is infected and so in the son. It appears that the father passed down the trait but it was really passed down from the mother who is a carrier.
• Happens with Consanguineous Union (cousins getting married)

• One X chromosome in each cell is randomly inactivated.
• Compensate for gene dosage between males and females.
• Inactivation is permanent. Happens at Implantation
• In females, sometimes show as mosaics.
• XIST silences chromosome

• acts through a epigenetic silencing mechanism.
• shuts down transcription of one of the X chromosomes in the cell.

What diseases are a result of Mitochondrial Inheritance?

• Leber's hereditary optic neuropathy (mutation in electron transport protein NADH-coenzyme Q)
• Cardiac and Skeletal muscle
• Nervous system

• Passed on by mother but daughter or son can get it.
• Offspring's mitochondria comes from mother's egg.
• Mutations involved with oxidative phosphorylation
• Can be spontaneuous
• Homoplasmy and heteroplasmy mutations.

Homoplasmy: all mitochondrial DNA in the cell has the same mutation.

Heteroplasmy: mix of mutated and normal DNA.

•  Imprinted genes undergo selective transcription ("imprint") that is dependent on the parental origin, although they have the same genomic DNA sequence
• Selective gene silencing from either maternal, or paternal allele
• Occurs during gametogenesis
• Disease manifestation is dependent on allelic lose o f normally transcribed gene.

• Recieving both copies of a chromosome from the say parent.
• 2 Maternal(Absent of Paternal) Prader Willi's
• 2 Paternal(Absent of Maternal) AngelMan

Can turn off a gene

• When there is a trisomy chromosome, one of the chromosomes will be kicked out.
• If the wrong one is kicked out it can lead to Uniparental Disomy

• overgrowth disorder
• gene IGF2 escapes epigenetic silencing

• Imprinting: programmed allelic exclusion
• X chromosome inactivation: random allelic exclusion.

Complicates Mendelian Penetrance

• Person has the disease genotype but does not express the phenotype.
• Can still pass it on to offspring.

Complicates Pedigree

• A child born with a disease for which there is no previous history of.
• Post-Zygotic mutation
• New autosomal dominant mutation, mimicking an autosomal  or X-linked recessive pattern

Complicates Pedigree

•  severity of disease can vary greatly.
• modified by environment, modifier genes or mutation at the disease locus.

Complicates Pedigree

• Environmental factors as well as multiple genes are responsible for the inheritance of a trait. (Like Type II Diabeties)

Complicates Pedigree

• Mutations of different genes on different chromosomes that have similiar phenotypes

Complicates Pedigree

• Different mutations within the same gene
• Example: Becker/Duchenne Muscular Dystrophy