Overview of genetic disorders and their implications.
Discussion on inbreeding and its effects on populations.
Importance of understanding genetic diversity through migration and interactions.
Inbreeding and Heterozygosity
Repeated inbreeding in a closed population leads to a reduction in heterozygotes.
Process known as "loss of heterozygosity".
Genetic disorders are predominantly homozygous recessive conditions.
Increased homozygosity correlates with a higher prevalence of genetic disorders in inbred populations.
Regular interaction with wider gene pools guards against the retention of deleterious alleles.
Types of Genetic Disorders
Autosomal Recessive Disorders
Characterized by the need for two copies of a mutated allele for expression.
Tay Sachs Disease
Affects mainly the Ashkenazic Jewish population.
Caused by deficiency in a lysosome enzyme that breaks down lipids in brain cells.
Symptoms include:
Vision impairment
Movement impairments
Hearing loss
Decreased mental development
Fatal by approximately age 5.
Cystic Fibrosis
Occurs across all ethnic groups, most common in Caucasians.
One in 29 Caucasians in the U.S. are carriers.
Caused by a defective chloride ion channel, impacting sodium and water transport.
Symptoms include:
Thick mucus in bronchial tubes and pancreatic ducts
Average lifespan extended to about 35 years due to improved understanding and treatments.
Results in severe respiratory and digestive complications.
Sickle Cell Disease
Anomalous sickle-shaped red blood cells leading to various health issues.
Most prevalent in people of African descent; one in 625 African Americans are carriers.
Causes include:
Anemia
Tissue damage
Increased susceptibility to infections
Higher stroke rates due to blocked blood vessels.
Classified as an incomplete dominance disorder: heterozygotes exhibit some symptoms but with mild effects compared to homozygous recessives.
Heterozygotes have moderate malaria resistance, highlighting an evolutionary balance between sickle cell disease and malaria's impact.
Autosomal Dominant Disorders
Characterized by the presence of a single mutated allele sufficient for expression.
Marfan Syndrome
Rare disorder affecting connective tissues.
Symptoms include:
Dislocated lenses
Long limbs and fingers
Abnormal chest shape
Affects fewer than 1 in 2000 individuals.
Osteogenesis Imperfecta
Influenced by mutations in genes responsible for type I collagen synthesis.
Results in brittle bones; approximately 1 in 5000 births.
Treatment options involve long-term drug therapies.
Huntington's Disease
Progressive neurodegenerative disorder caused by mutated protein gene accumulation in neurons.
Typical clinical onset in late 30s to early 40s.
Symptoms include:
Uncontrolled movements (Huntington's chorea)
Unsteady gait
Dementia and speech impairment
Recent gene therapy research shows promise for extending lifespan post-symptom onset.
Inheritance Patterns
Simple Dominance and Recessivity
One gene controls the traits, with dominant and recessive forms determining expression.
Polygenic Traits
Traits controlled by multiple allelic pairs and facilitate a range of expressions, like height and skin color.
Examples:
Skin color is influenced by over 100 genes, resulting in diverse human pigmentation across populations.
Environmental factors interact with polygenic traits, leading to conditions like allergies and other diseases.
Multifactorial Traits - traits influenced by both genetic and environmental factors (e.g., diabetes, schizophrenia).
Codominance
Expression where both alleles in a heterozygote manifest equally.
Example: Human blood types (A, B, O).
Alleles A and B are dominant; O is recessive.
By requiring dominance expressions in different allele combinations, codominance shapes blood phenotype expression.
Sex-Linked Traits
Genes located on sex chromosomes (X or Y).
Most frequently studied sex-linked traits are X-linked due to various genetic factors.
Color Blindness as an exemplary X-linked disorder.
Male offspring inherit X chromosome from mother (dominant or recessive); express allele phenotype directly due to lack of a second X chromosome.
Punnett square analysis illustrates the probabilities of offspring genotype distribution, emphasizing male susceptibility to X-linked traits.
Carrier daughters and color blind sons result from specific genetic crosses.
Historical Context of Genetic Disorders
Genetic disorders have historical relevance in royal families due to inbreeding practices.
Queen Victoria's lineage exemplifies hereditary conditions, such as hemophilia, resulting from carries severe hereaditary issues stemming from existing recessive traits.
Summary and Conclusion
Complexity of inheritance and expression necessitates understanding diverse genetic interactions and their results in terms of disorders.
Noteworthy that many disorders (both dominant and recessive) can have extensive implications on health and society within genetic frameworks and environmental interactions.
Questions and Discussion
Opportunity for attendees to inquire further about specific topics or elucidations.