Inheritance 10.2 HL

Inheritance has been covered in the SL genetics topic already so this HL topic covers dihybrid crosses and the discovery of linkage by Morgan with Drosophila flies. The prediction of phenotype ratios using larger Punnett squares is required as is the understanding of how phenotype ratios of 9:3:3:1 or 1:1:1:1 ratios can appear. The ideantification of recombinant phenotypes is important and so is the ability to recognise signs of linkage.


Key words

Learn and test your biological vocabulary using these 10.2 Inheritance flashards.

Clean sweep - quick revision through the whole topic

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - great revision.

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Structured question about inheritance

Explaining the proccess of Mendelian inheritance is an important skill from this topic.

Answer the question below on a piece of paper, then check your answer against the model answer.

In the mustard plant Arabidopsis (Arabidopsis thaliana), there are two genes which affect plants: The tallness gene and the leaf shape gene. The allele for tall plants is T (dominant) and the allele for short plants is t. The allele for round leaves is R (dominant) and the allele for oval leaves is r.

a) Determine the phenotype of a plant with the genotype: Ttrr.       [1].

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b) Plants which are tall with round leaves are crossed with plants that are short with oval leaves.
    Surprisingly all the 1000 offspring were tall with round leaves.

   Deduce the genotype of the offspring                                            [1]

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c) In another cross offspring from (b) were crossed and four different phenotypes were found in the offspring.
   Suggest what the phenotype ratio of offspring would be.               [2]

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d) Identify the recombinant phenotypes in this cross.                    [1]

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Revision summary list for 10.2 Inheritance

10.2 Inheritance

Linked genes

  • Genes are linked when they occur on the same chromosome.
  • Unlinked genes show independent segregation in meiosis.

Polygenic inheritance

  • Variation between living can be discrete or continuous.
  • Phenotypes controlled by many genes (polygenic) show continuous variation. They may also be influenced by environmental factors.
  • Chi-squared tests are used to calculate if differences between observed and expected frequencies are statistically significant.

Student skills and applications

  • A awareness of Morgan’s discovery of non-Mendelian ratios in Drosophila.
  • The ability to complete Punnett squares for dihybrid traits and analyse them.
  • Ability to calculate predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.
  • The skill to identify recombinants in crosses involving two linked genes and to understand when they are shown as vertical pair in crosses of linked genes.
  • The skill to use of a chi-squared test on data from dihybrid cross.

Revision mindmap

This diagram summaries the main sections of topic 10.2 Inheritance HL
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Review questions

This is a self marking quiz containing questions covering the topic outlined above.
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Revision fun activity

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