What is a genotype and phenotype ratio?

1 Answer
Nov 29, 2015

Genotype is the *genetic make-up * of an organism . It describes about the nature of each allele .

Phenotype is the morphology of an organism .


The genotype is expressed as phenotype when the information encoded in the genes is used to make protein and RNA molecules.

Consider an example :
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Here , we have crossed a heterozygous ( the two alleles show dominant and recessive relationship vix T and t ) male gamete with a heterozygous female gamete .

We get the progenies as
1 ) TT homozygous ( the two alleles are of same type ) : TALL PLANT
2) Tt heterozygous :TALL PLANT ( since T is dominant over t )
3) Tt
4) tt homozygous :DWARF PLANT

Here the Phenotype (morphology) of the plant shows you :
3 : 1 ratio (Tall plants :Dwarf plants)
Just consider how the plant heights look to you externally)

However , if you consider the genotypic ratio i.e genetic make up , you consider the nature of genes i.e heterozygous or homozygous .
According to that , we have a ratio : 1 :2 :1 (homozygous tall :heterozygous tall :homozygous short )

Note : Recessive alleles will always express themselves in homozygous conditions.

Also , it is not necessary that Phenotypic ratio is always different from Genotypic ratio. We consider there studies in Non - Mandelian Inheritance , examples of which are
1) Incomplete dominance
2) Codominance , e.t.c