- Key words
- Clean sweep - quick revision through the whole topic
- Structured question about inheritance
- Model answer
- Revision summary list for 10.2 Inheritance
- 10.2 Inheritance
- Revision mindmap
- Review questions
- 10.2 Inheritance HL 1/1
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.
Read the slides and look up any words or details you find difficult to understand.
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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Click the + icon to see a model answer.
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
Test if you can draw something like these concept maps from memory.
Review questions
This is a self marking quiz containing questions covering the topic outlined above.
Try the questions to check your understanding.
START QUIZ!
Which tem best describes linked genes?
Linked genes are linked when they occur on the same chromosome.
What is a feature of unlinked genes?
Unlinked genes show independent segregation in meiosis but linked genes don't.
Which of the features is most likely to be controlled by polygenic inheritance and for what reason?
Polygenic inheritance is when a feature is controlled by more than two genes, and when each gene contributes a part of the genotype.
It is more common that it looks like continuous variation, as with just two genes and two alleles there can be five phenotypes.
When would a biologist use a chi-squared test?
Chi-squared tests are used to calculate if differences between observed and expected frequencies are statistically significant
Morgan crossed white eyed male fruit flies with heterozygous wild type (red eyed) females.
What was unusual about his results which suggested the presence of linked genes?
Morgan discovered non-Mendelian ratios in Drosophila.
The ability to complete Punnett squares for dihybrid traits and analyse them is an important skill.
This punnett square was drawn by an IB student.
What were the genotypes of the parents in this cross?
Ability to calculate predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes.
In this example, the test is to work backwards from the gametes to the parents.
This punnett square was drawn by an IB student who was lpredicting the number of offspring who have different phenotpyes. The offspring with brown curly fur have been circled.
What is the ratio of offspring phenotypes in this grid?
In this example the ratio is 9:3:3:1 - genes with no linkage and two double heterozygous parents have this ratio of offspring phenotypes.
Which of the following would be considered a "recombinant phenotype"?
The skill to identify recombinants in crosses involving two linked genes is important.
The phenotypes are different from the 'grandparents' in recombinant phenotypes.
So green
Revision fun activity
Everyone needs a bit of fun while they revise. Try this Inheritance card matching game.
Can you reach the leaderboard?