K

last lec before exam

Introduction to Genetic Disorders

  • 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.