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TASBiologyQuick questions
Unit 3: Heredity and Continuity of Life
Quick questions on Inheritance and Variation - TCE Biology (Tasmania)
5short 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 are monohybrid crosses?Show answer
A monohybrid cross follows a single gene. A Punnett square predicts offspring ratios. Crossing two heterozygous tall plants (Tt x Tt) gives offspring in the ratio 1 TT : 2 Tt : 1 tt, a genotype ratio of 1:2:1. Because T is dominant, the phenotype ratio is 3 tall : 1 short.
What are dihybrid crosses?Show answer
A dihybrid cross follows two genes at once. Crossing two individuals heterozygous for both genes (for example RrYy x RrYy in peas, where R is round and Y is yellow) gives the classic 9:3:3:1 phenotype ratio: 9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green. This ratio only holds when the two genes assort independently, which requires them to be on different chromosomes (or far apart on the same chromosome).
What is variations on simple dominance?Show answer
Not all inheritance is simple dominant and recessive.
What are pedigrees?Show answer
A pedigree is a family tree that tracks a trait across generations. Squares represent males, circles represent females, and shaded symbols are affected individuals. By analysing who is affected, you can deduce whether a trait is dominant or recessive and whether it is autosomal or sex-linked. For example, if two unaffected parents have an affected child, the trait must be recessive, because the parents both carried a hidden allele.
What is sources of variation?Show answer
Genetic variation within a species comes from three main sources:
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