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Module 5: Heredity
Quick questions on Codominance, incomplete dominance and multiple alleles explained: HSC Biology Module 5
9short 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 is 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 worked ABO cross?Show answer
Father type A heterozygous ($I^A i$) × Mother type B heterozygous ($I^B i$).
What is notation?Show answer
Use uppercase letters with superscripts. For ABO blood groups: $I^A$ and $I^B$ are codominant.
What is confusing codominance with incomplete dominance?Show answer
Codominance = both visible (AB blood, both antigens). Incomplete dominance = blended intermediate (pink, between red and white).
What is wrong allele notation for ABO?Show answer
Use $I^A$, $I^B$, and $i$ (lowercase i for recessive O). Writing A, B, O directly without the I superscript loses marks.
What is forgetting that each person has only two alleles?Show answer
Multiple alleles exist in the population, but each individual still inherits one allele from each parent (total two).
What is assuming all O offspring need O parents?Show answer
Two heterozygous parents ($I^A i$ × $I^B i$, for example) can produce an O child even though neither parent is O.