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TEST CROSS How to tell the difference between homozygous and heterozygous individuals that have dominant phenotypes © 2016 Paul Billiet ODWS.

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Presentation on theme: "TEST CROSS How to tell the difference between homozygous and heterozygous individuals that have dominant phenotypes © 2016 Paul Billiet ODWS."— Presentation transcript:

1 TEST CROSS How to tell the difference between homozygous and heterozygous individuals that have dominant phenotypes © 2016 Paul Billiet ODWS

2 Selfing or test cross? Plants can be selfed
Homozygous plants (AA) are pure breeding Heterozygotes (Aa) will give 75% dominant (AA and Aa) and 25% recessive (aa) phenotypes in their offspring Animals are not usually hermaphroditic so they cannot be selfed Animals require a test cross to be carried out (these days use a gene probe). © 2016 Paul Billiet ODWS

3 Coat colour in mice Traits Alleles Genotypes Phenotypes Grey G GG White g Gg gg 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. © 2016 Paul Billiet ODWS

4 Homozygous Grey White GG G Gg 100% 0%
Phenotypes x White Genotypes GG gg Gametes G g Gg Offspring 100% 0% © 2016 Paul Billiet ODWS

5 Heterozygous Grey White Gg G g 50%
Phenotypes x White Genotypes Gg gg Gametes G g Offspring 50% © 2016 Paul Billiet ODWS

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