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NSWBiologyQuick questions
Module 5: Heredity
Quick questions on Codominance, incomplete dominance and multiple alleles explained: HSC Biology Module 5
8short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is codominance?Show answer
In codominance, both alleles in a heterozygote are fully and simultaneously expressed. The phenotype shows both traits side by side, NOT blended.
What is incomplete dominance?Show answer
In incomplete dominance, the heterozygote shows an intermediate phenotype between the two homozygotes, as if the alleles had been blended.
What are multiple alleles?Show answer
Most genes in textbooks have just two alleles (e.g. A and a). In reality, many genes have multiple alleles in the population.
What is notation?Show answer
Use uppercase letters with superscripts. For ABO blood groups: and are codominant.
What is wrong allele notation for ABO?Show answer
Use , , and (lowercase i for recessive O). Writing A, B, O directly without the I superscript loses marks.
What is q1?Show answer
In horses, the gene for coat colour shows incomplete dominance. Chestnut () crossed with cremello () produces palomino () foals. A breeder crosses two palomino horses.
What is q2?Show answer
A woman with blood type O has a child with blood type AB. The mother claims a particular man is the father. The man has blood type A (genotype ).
What is q3?Show answer
Sickle cell trait shows codominance at the molecular level. (a) Define codominance. (b) An heterozygote produces both normal and sickle haemoglobin in red blood cells - explain how this is consistent with codominance.