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TEST CROSS How to tell the difference between homozygous and heterozygous individuals that have dominant phenotypes.

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

1 TEST CROSS How to tell the difference between homozygous and heterozygous individuals that have dominant phenotypes

2 Selfing or test cross? Plants can be selfed (crossed with themself!)
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 to determine phenotype © 2007 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 © 2007 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% © 2007 Paul Billiet ODWS

5 Heterozygous Grey White Gg G g 50%
Phenotypes x White Genotypes Gg gg Gametes G g Offspring 50% © 2007 Paul Billiet ODWS

6 Understanding Pedigree Charts

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