The ratio of genotypes observed in progeny after a cross has been performed is called genotypic ratio.

Genotype refers to the genetic makeup of an organism, which consists of the combination of alleles (alternative forms of a gene) inherited from its parents. When a cross is performed between two individuals that differ in their genotype, the resulting offspring can exhibit different combinations of alleles.

The genotypic ratio is a representation of the different genotypes observed in the progeny after a cross. It describes the relative frequencies or proportions of each possible genotype among the offspring. The genotypic ratio is determined by the laws of Mendelian inheritance, which govern the transmission of alleles from parents to offspring.

Example:
Let's consider a cross between two pea plants with different genotypes for flower color. One plant has the genotype RR (homozygous dominant for red flowers) and the other has the genotype rr (homozygous recessive for white flowers). When these two plants are crossed, the resulting progeny will have a genotypic ratio of 1:0:0, representing the genotypes RR:Rr:rr.

This genotypic ratio indicates that all the offspring will have the genotype RR (homozygous dominant) for red flowers. This is because the dominant allele (R) masks the expression of the recessive allele (r). In this case, the genotypic ratio is a reflection of the phenotypic ratio as well, since the phenotype (observable characteristic) of flower color is directly related to the genotype.

Key Points:
- The genotypic ratio describes the relative frequencies or proportions of different genotypes observed in the offspring after a cross.
- It is determined by the laws of Mendelian inheritance, which govern the transmission of alleles from parents to offspring.
- The genotypic ratio is a reflection of the genetic makeup of the progeny and can be used to predict the inheritance patterns of specific traits.
- The genotypic ratio may or may not correspond to the phenotypic ratio, depending on the dominance relationships between alleles and the expression of the traits.