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Powerpoint Presentation: Test Cross

 

Genetics Index

Chromosomes
Meiosis
Meiosis: Crossing over
Mitosis and Meiosis
Introduction to Mendelian Genetics
Codominance
Multiple Alleles
Pedigree Charts
Twin Studies
The dihybrid cross
Dihybrid Cross : Test Cross
Autosomal Linkage
The Genetic Diagram for Linked Genes
Calculating the cross over value using a test cross
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

Topic Chapters Index

 

GENETICS

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Test Cross

One problem that must be solved is how to tell the difference between homozygous and heterozygous individuals that have dominant phenotypes.

Plants could be selfed. Homozygous plants are pure breeding but heterozygotes will give 75% dominant and 25% recessive phenotypes in their offspring.

Animals are not usually hermaphroditic so they cannot be selfed.

Animals require a test cross to be carried out (though these days a gene probe is more likely to be used).

Example: Character: Coat colour in mice

coat colour in mice

 

Grey mice could have one of two different genotypes, GG or Gg.

If they are crossed with a white mouse (gg) these genotypes will give two different results.

 

test cross mice

A test cross is also used to determine the proportions of gametes carrying different alleles.

 

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