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Powerpoint Presentation:Linkage

 

Genetics Index

Chromosomes
Meiosis
Meiosis: Crossing over
Mitosis and Meiosis
Introduction to Mendelian Genetics
Test Cross
Codominance
Multiple Alleles
Pedigree Charts
Twin Studies
The dihybrid cross
Dihybrid Cross : Test Cross
Autosomal Linkage
The Genetic Diagram for Linked Genes
Sex determination and sex linkage
Sex linkage
Genetic diagram for sex linked genes
Blood Clotting and Haemophilia
The Retina and Daltonism
Genetic Modification
Cloning Animals
Cloning Plants

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GENETICS

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Calculating the cross over value using a test cross

I. Drosophila: Studying the wing shape and body colour

Drosophila test cross

 

test cross

 

These results are, therefore, typical of non-linked genes. The recombinants are in the same frequency as the parental combinations. Note: In this example bent wing flies are a bit crippled so their offspring are not so viable. This accounts for their low numbers.

 

II. Drosophila: Studying the eye colour and body colour

drosophila test cross

 

test cross

The frequency of the recombinants is less than 50% this is an example of linkage.

The % recombination in a test cross is called the cross over value.

The cross over value between ebony and pink  = cross over value between ebony and pink

This value is important as it tells us how far apart the loci of the genes are. Cross over values from several pairs of genes will permit a geneticist to plot a gene map of the chromosome.

 

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