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WABiologyQuick questions
Unit 3: Continuity of Species
Quick questions on Patterns of inheritance: WACE Year 12 Biology
3short 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 dihybrid inheritance?Show answer
A dihybrid cross follows two genes at once. When an individual heterozygous for both genes is crossed with another (for example RrYy by RrYy), the offspring show a characteristic 9:3:3:1 phenotype ratio, provided the two genes assort independently. This ratio reflects independent assortment in meiosis, where the alleles of one gene separate independently of the other.
What are multiple alleles?Show answer
A gene can have more than two alleles in a population, even though any individual carries only two. The human ABO blood group is the classic example: the alleles are I^A, I^B and i. I^A and I^B are codominant with each other, and both are dominant over i. This gives four blood groups (A, B, AB and O) from three alleles.
What is choosing the right pattern?Show answer
The key skill is reading a problem and identifying the pattern: a 3:1 ratio suggests simple dominance, 9:3:3:1 suggests a dihybrid cross, three phenotypes from a cross of two heterozygotes suggests incomplete dominance or codominance, a trait far more common in males suggests sex linkage, and a continuous range suggests polygenic inheritance. Once the pattern is clear, the correct symbols and Punnett square follow.
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