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Inheritance and Evolution
Quick questions on Dihybrid inheritance and independent assortment: H2 Biology Inheritance and Evolution
6short 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 two genes at once?Show answer
A dihybrid cross follows two genes. If they are on different chromosomes (or far apart on the same one), they are inherited independently.
What is the law of independent assortment?Show answer
The law of independent assortment states that the alleles of one gene segregate into gametes independently of the alleles of another gene. So a TtRr individual makes four equally likely gametes: TR, Tr, tR and tr.
What is the 9?Show answer
Crossing two double heterozygotes (TtRr x TtRr) and combining all sixteen gamete combinations gives a 9:3:3:1 phenotypic ratio: 9 showing both dominant traits, 3 showing the first dominant and second recessive, 3 the reverse, and 1 showing both recessive. This ratio is the signature of two independently assorting genes, each heterozygous.
What is q1?Show answer
State the phenotypic ratio expected from a cross between two organisms heterozygous for two unlinked genes. [1 mark]
What is q2?Show answer
State the four types of gamete produced by an organism with genotype AaBb, assuming the genes assort independently. [1 mark]
What is q3?Show answer
A chi-squared test gives a calculated value greater than the critical value at the 0.05 level. State the conclusion. [1 mark]
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