What is the expected genotypic ratio resulting from a heterozygous x heterozygous monohybrid cross?

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bandmanjoe | Middle School Teacher | (Level 2) Senior Educator

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The genotype of an organism is the genetic makeup that organism possesses as a result of the genes it inherited from its parents genotyope.  If we are again using the trait of tallness in pea plants, with the tall (T) being dominant to short (t), we have the cross of two plants that are hybrid tall (Tt):

             T           t

T           TT         Tt


t            Tt         tt

The Punnett Square used above (imagine the box and the lines) shows we have 1/4 offspring with the genotype of TT, purebred tall.  We have 2/4 offspting with the genotype of Tt, hybrid tall.  We also have 1/4 offsring with the genotype of tt, purebred short.  This gives us the following breakdown of genotypes from this cross:

TT, 25%             Tt, 50%             tt, 25% 


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