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please help me If a heterozygous dominant tall pea plant is crossed with a short pea plant, what is the expected phenotypic ratio of tall:short plants? 1:1 1:2 3:1 all tall all short



Answer :

brissaax
dominant trait = T (tall)
recessive trait = t (short)

heterozygous, meaning different, tall pea plant = Tt
short, short being recessive, pea plant = tt

phenotype means physical looks, which is either tall or short

T t

t | Tt tt
t | Tt tt

two Tt & two tt meaning there are 2 tall and two short. therefore,
1:1
marianaegarciaperedo

Assuming a diallelic gene exhibiting complete dominance, with tall plants being the dominant phenotype and short plants the recessive one, the cross of a heter0zyg0us plant with a short one results in a phenotypic ratio 1:1.

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We know that the cross involved a heter0zyg0us dominant tall pea plant and a short pea plant.

We will assume a diallelic gene coding for this trait, and exhibiting complete dominance. This means that the dominant allele completely masks the expression of the recessive allele.

So,

  • h0m0zyg0us dominant genotype    ⇒     dominant phenotype
  • heter0zyg0us genotype                    ⇒     dominant phenotype
  • h0m0zygous recessive genotype    ⇒     recessive phenotype

If the heter0zyg0us plant exhibits the dominant phenotype, it means that the allele coding for tall plants in the dominant allele.

So let us say that

  • T is the dominant allele that codes for tall plants
  • t is the recessive allele that codes for short plant

According to this information, the tall plant is Tt and the short plant is tt.

So let us make the cross,

Cross:  tall plant with short plant

Parentals)    Tt      x       tt

Gametes)   T     t        t     t

Punnett square)      T            t

                       t       Tt            tt

                       t       Tt            tt

F1) Genotype

  • 2/4 = 1/2 = 50% of the progeny is expected to be heter0zygous, Tt
  • 2/4 = 1/2 = 50% of the progeny is expected to be h0m0zyg0us recessive, tt

Genotypic ratio ⇒ 1:1

    Phenotype

  • 2/4 = 1/2 = 50% of the progeny is expected to be tall plants
  • 2/4 = 1/2 = 50% of the progeny is expected to be short plants

Phenotypic ratio ⇒ 1:1

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