PPT 10

Non-Mendelian Genetics Overview

Simple Autosomal Recessive Inheritance
- Trait determined by one gene on an autosome.
- Only expressed by homozygous recessive individuals.
- Certain diseases are common in specific populations.

Traits can skip generations.
Equal chance of expression in males and females.
Carrier: An individual who carries the recessive allele but does not exhibit the disease.
Both parents must be carriers to pass the disease to their children, often found in closely related individuals.
Homozygous recessive individuals (aa) are not considered carriers.

Mutation in the gene controlling salt and water balance in cells.
Symptoms: Thickened mucus causing respiratory and digestive issues.
Carrier Statistics: 1 in 20 White North Americans are carriers (genotype Cc).
Homozygous recessive (cc) individuals cannot be carriers as CF is deadly; they do not reproduce.
Genetic analysis and medical symptoms (e.g., sweat test) are used for diagnosis.
Mandatory screening for newborns in North America, including Quebec.

Common among Eastern European Jews and French Canadians.
Caused by enzyme malfunction leading to brain swelling and potentially death by age 5.
Genetic mutation leading to a frameshift in the HEXA gene.

Epidemiology: 1 in 4 Black people in Central Africa are carriers.
Carriers of the sickle cell trait may have a survival advantage in malaria-prone regions.
Symptoms include susceptibility to infections, severe pain crises, and complications with overexertion and altitude.
Crystallization of hemoglobin under low oxygen levels deforms red blood cells into a sickle shape, reducing their ability to carry oxygen.

Affected individuals have at least one dominant allele ( H) and usually have an affected parent.
Traits produced by one gene site on an autosome, independent of gender.
Major conditions: Dwarfism and Huntington's Disease.
- Dwarfism: Caused by double dominance; lethal in some cases.
- Huntington’s Disease: Neuromuscular degeneration that manifests in mid-adulthood (40s-50s); inheriting one allele is sufficient for disease expression.

Recessive traits require both parents to carry the allele for expression.
Dominant traits require only one affected parent, leading to potential purging of harmful alleles over generations.

Traits located on the X chromosome.
Males have a higher chance of expressing recessive traits on the X chromosome; examples include color blindness and hemophilia.

Pedigrees track inheritance patterns within families, identifying carriers and affected individuals.
Useful for understanding genetic diseases, as patterns can be analyzed across generations.

In female mammals, one X chromosome becomes inactive (Barr body) early in embryonic development, ensuring dosage compensation between sexes.
This random inactivation results in females being mosaics for X-linked traits.

Incomplete Dominance: Offspring exhibit a phenotype that is a blend of the parents' traits (e.g., Snapdragons).
- Example: Red (CR CR) x White (CW CW) = Pink (CR CW).
Co-Dominance: Both alleles contribute to the phenotype without blending.
- Example: Blood types A (IA) and B (IB) are co-dominant.

Polygenic Inheritance: Multiple genes influence a single trait (e.g., human height).
Multifactorial Inheritance: Genetic and environmental factors influence traits, leading to conditions that can run in families.