BOGO Biology - Sex-Linked Traits: Hemophilia

Introduction

• Topic: Sex-linked traits with a focus on hemophilia.
• Human somatic cells have 46 chromosomes (23 pairs).
  • One set of genes from mother, one set from father.
  • Pairing forms homologous pairs.

Chromosome Pairs

• 23 chromosome pairs; one pair determines biological sex.
  • X chromosome: larger, longer.
  • Y chromosome: smaller, shorter.
• Females: XX
• Males: XY
• Male sperm determines sex of offspring:
  • X chromosome = female offspring
  • Y chromosome = male offspring

Sex-Linked Traits

• Traits on X or Y chromosomes.
• Examples:
  • SRY gene (Y chromosome): development of testes in males.
  • AR gene (X chromosome): male pattern baldness.

Hemophilia: Recessive X-Linked Trait

• Normal coagulation process:
  • Vessel constriction and coagulation cascade activate platelets.
  • Platelets form a clot to stop bleeding.
• Hemophilia:
  • Coagulation process disrupted, leading to ineffective clotting.
  • Fatal bleeding risk from small wounds.

Genetic Transmission of Hemophilia

• Male Dominance:
  • Males: Only one X chromosome, Y cannot overshadow mutation.
  • If X chromosome has mutation, males develop hemophilia.
• Female Carrier Status:
  • Females: Two X chromosomes.
  • One mutated X: Carrier, but not affected due to dominant healthy gene on other X.
  • Rare to inherit two mutated X chromosomes (1 in 25 million chance).

Inheritance Patterns

• Carrier females can pass gene to offspring:
  • Daughter: becomes a carrier.
  • Son: develops hemophilia.
• Reproduction with healthy male:
  • 50% chance daughter is a carrier.
  • 50% chance son has hemophilia.

Historical Context

• Example: Royal families of Europe.
• Queen Victoria was a carrier.
  • Passed mutation to children.
  • Affected royal houses in Germany, Spain, Russia.
  • Hemophilia in Tsar Nicholas II’s son influenced the downfall of Tsarist regime.

Conclusion

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