10.2+Dihybrid+crosses+and+gene+linkage

10 Genetics - 10.1 Meiosis - 10.2 Dihybrid crosses and gene linkage - 10.3 Polygenic inheritance - Genetics Labs

10.2 Dihybrid crosses and gene linkage

 * Assessment statements ** (IBO notes added to some point to clearly indicate what needs to be understood and what does not)
 * 10.2.1 || Calculate and predict the genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes. Alleles are usually shown side by side in dihybrid crosses, for example, TtBb. ||
 * 10.2.2 || Distinguish between autosomes and sex chromosomes. ||
 * 10.2.3 || Explain how crossing over between non-sister chromatids of a homologous pair in prophase I can result in an exchange of alleles. ||
 * 10.2.4 || Define linkage group. ||
 * 10.2.5 || Explain an example of a cross between two linked genes. When representing crosses involving linkage show alleles as vertical pairs seperated by twin horizontal lines (representing the chromosomes). ||
 * 10.2.6 || Identify which of the offspring are recombinants in a dihybrid cross involving linked genes. ||


 * Practise Assessment Questions** (from past papers)

In some maize plants the seed is enclosed in a green sheath called a tunica. The allele (T) for this is dominant to the allele (t) for normal, unenclosed seeds. The endosperm of the seed can be starchy (allele E) or sugary (allele e). The genes for these two characteristics are linked. The table below shows the outcome of crosses between a plant heterozygous for both characteristics and one that is homozygous recessive for both characteristics.
 * Phenotype || number ||
 * Tunica present, starchy || 326 ||
 * Unenclosed seeds, starchy || 111 ||
 * Tunica present, sugary || 118 ||
 * Unenclosed seeds, sugary || 295 ||


 * 1) State the genotype of the heterozygous parent using the correct notation. [1]
 * 2) Identify which individuals are recombinants in this cross. [1]
 * 3) Explain what has occurred to cause these results. [4]

Log in to the [|DCS Bridge] to obtain your workbooks and supporting resources
 * Workbooks and Worksheets **

An alternative set of notes from [|i-Biology] can be found here media type="custom" key="24774576"

Steven Taylor ([|i-Biology]) has a great presentation to view and take notes from before starting your notebook media type="custom" key="24774578"
 * Presentations and tutorials **

The khan academy has a video tutorial on 'punnett square fun' which looks at some ideas in theoretical genetics including dihybrid crosses media type="custom" key="24774580"

Bozeman Science video tutorials on: Punnett Squares (second half is on dihybrid crosses) media type="custom" key="24774582" Linked genes media type="custom" key="24774584"

[|Dihybrid crossing tutorial]by the college of Siskiyous

Use [|click4biology] to review and complete your notes

> a. [|Dihybrid crossing] > b. [|Sex linked inheritance]
 * Activity Suggestions **
 * 1) Work with a partner decide whether you are taking notes on 10.2.1-10.2.3 or on 10.2.4 to 10.2.6
 * 2) Look through the resources above whilst reviewing them take notes
 * 3) Switch partners with another group and teach each other your assessment statements
 * 4) Check your understanding (and supplement your notes where necessary using the questions from the Biology project on:
 * 1) Switch back to your original pair discuss your findings and work together on completing your workbook (mini-tutorials will be available)