Co-dominace

• Co-dominace

  • A form of inheritance in which the phenotypes of both parents alleles are expressed equally and are not blended together.
• Example 1 - short horned cattle

  • When you cross a red cow with a white cow, the offspring do not exhibit the phenotypes of one parent but instead show both parent’s phenotypes - by having red and white spots.
  • This is called roan
  • Lets say that a red cow allele is represented by R, while a white cow allele is represented by W
  • Neither gene is dominant so both are capitals.
• Example 2 - Sickle cell Anaemia

  • Normal erythrocytes contain the protein haemoglobin for carrying oxygen and have a biconcave disc shape
  • If a person has sickle cells their haemoglobin isn’t formed properly and their erythrocytes are a sickle (crescent) shape - the problem = carries less oxygen
  • This makes the patient anaemic
  • Sickle cell anaemia is codominantly inherited
  • Normal erythrocyte allele is A
  • The sickle cell allele is S
  • Neither gene is dominant so both are capitals
• Incomplete dominance

  • A form of inheritance in which both alleles of a gene at a locus are partially expressed often resulting in an intermediate or different phenotype.

   
• Example - red, white and pink flowers

  • RR - red flowers
  • Rr - pink flowers
  • rr - while flowers

   

  • Crossing a red and white flower:
  • F1 genotype - 100% Rr
  • F1 phenotype - 100% pink