Understanding Platelets and Hemophilia

Jan 16, 2025

Lecture Notes: Platelets and Sex-Linked Traits

Introduction to Platelets

  • Platelets are fragments of cells that help in blood clotting.
  • Function: Prevents excessive bleeding by forming clots.
  • Disorder: Hemophilia affects platelet function, leading to continuous bleeding even from small cuts.

Hemophilia

  • Description: A sex-linked, recessive genetic trait affecting blood clotting.
  • History: Treatments have greatly improved, though it was not always the case.
  • Genetics:
    • Sex-Linked Trait: Involves sex chromosomes (X and Y).
    • Mendelian Genetics: Differs as it involves sex chromosomes.

Human Chromosomes

  • Karyotype: Humans have 46 chromosomes in 23 pairs.
    • 23 from egg, 23 from sperm.
    • Last pair are sex chromosomes: XX (female), XY (male).
  • Sex Chromosomes:
    • X chromosome is larger and contains more genes than Y.
    • Traits tracked in sex-linked genetics are often on X chromosome.

Punnett Squares and Sex-Linked Traits

  • Understanding Punnett Squares: Used to predict genetic traits.
  • X-Linked Traits:
    • X-linked traits are often recessive.
    • Notation: "H" for non-hemophilia (dominant), "h" for hemophilia (recessive).
    • Female Genotypes:
      • XHXH or XHXh: No hemophilia (XHXh is a carrier).
      • XhXh: Has hemophilia.
    • Male Genotypes:
      • XHY: No hemophilia.
      • XhY: Has hemophilia.

Genetic Probability and Outcomes

  • Example Problem: Calculate the likelihood of a child having hemophilia from two non-hemophiliac parents, where the female is a carrier (XHXh, XHY).
  • Results: 25% chance for a child with hemophilia (male).

Important Considerations in Sex-Linked Traits

  1. Trait Assumptions: Do not assume traits are sex-linked; most are autosomal.
  2. Occurrence: Recessive traits more common in males (XY) since they have only one X chromosome.
  3. Dominant Traits: Sex-linked dominant traits exist; one dominant allele results in trait expression.
  4. Complex Genetics: Not all genetic disorders follow simple Mendelian inheritance (e.g., preeclampsia).
  5. Other Organisms: Other species may have different systems for sex determination (e.g., birds: Z and W chromosomes).

Conclusion

  • Encouragement to Explore: Stay curious about genetics and explore more through further reading and videos.

This lecture summarizes the basics of platelets, the genetic basis of hemophilia, and the application of Punnett squares to understand sex-linked traits, with a focus on human genetics and broader biological concepts.

Full transcript