Question

In a hybrid cross, how are the genotype and phenotype ratios determined?

Answer 1

These are related to the genetic and physical characteristics of an organism. This can be determined with the help of crossing. This crossing should be done between the ${ F }_{ 1 }$ generation hybrid with the individual bearing double or homozygous recessive traits.

Complete answer:
In a hybrid cross, the genotype and phenotype ratios are determined with the help of a test cross. The phenotype of the plant can be determined by a mere glance at it but to determine the genotype of a plant whether it is homozygous or heterozygous it should be test crossed with the plant bearing homozygous recessive traits. Let us try to understand this with the help of the following example.
We have a plant with an axial flower position and we know that the axial flower position trait is dominant over the recessive trait of the terminal flower position. So we can say that our plant is having a dominant gene over axial flower position and this is the phenotype of the plant which can be understood with a mere glance at it.
-Let us consider the alleles (A) represents the dominant trait for the axial position and (a) represents the recessive trait for the terminal position.
-Now to determine the genotype of our plant the only way to know that is to test it with a plant whose genotype is known to us.
-For this, we will take a plant with recessive traits that means a plant with terminal flower (aa).
This known genotype is crossed with our plant with an unknown genotype.
-There will be two possibilities of unknown genotype hanging homozygous (AA) dominant trait or heterozygous (Aa) dominant trait as we know the phenotype of our plant.
-Now we will cross our plant bearing axial flower (AA) or (Aa) with the plant bearing terminal flower (aa).
-The possible results will be either all the offspring bearing axial flower having traits (Aa) if our plant is having homozygous dominant trait (AA), or half of the offsprings bearing axial flower with the trait (Aa) and half is bearing terminal flower with the trait (aa) if our plant is having heterozygous dominant trait (Aa).
-So, with the help of the above explanation, we can easily determine the genotype of a plant.

Note:
-The phenotype of the plant can be determined by a mere glance at it.
-The test cross is a cross between the hybrid of ${ F }_{ 1 }$ generation with the plant with homozygous recessive traits.
-With the help of the testcross method we can determine the genotype of a plant.