How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous?
a) self-pollinate the green-pod plant.
b) cross the green-pod plant with another green-pod plant.
c) cross the green-pod plant with a yellow-pod plant.

C

Explanation:

Homozygosity is when the two alleles (gene form) are the same while heterozygosity is when the alleles are of different types.

In a gene, an allele is capable of masking the expression of another. The allele being expressed or that masks is called the DOMINANT allele while the allele being masked is the RECESSIVE allele.

A recessive allele will only be expressed (phenotypically) if the two alleles are of the same type i.e. homologous but when a dominant phenotype is expressed, one cannot ascertain whether the organism is heterozygous or homozygous for that gene. e.g T is the gene coding for height in plant, T which represents tallness is dominant over t, representing shortness. In a heterozygous (Tt) and homozygous dominant (TT) state, the plant will be phenotypically tall but will only be short in a homozygous recessive (tt) state.

Since the plant will be tall in homozygous (TT) or heterozygous (Tt), we cannot detect the actual genotype of the plant. Hence, a test cross is done.

A test cross is a cross between a dominant phenotype and a homozygous recessive in order to determine the actual genotype of the dominant organism i.e. whether homozygous or heterozygous.

In this case involving pod color gene, since the botanist is trying to determine whether the genotype of the green pod plant is heterozygous or homozygous, it means the allele for green pod is dominant over that of yellow pod (recessive).

N.B: The recessive trait can only be expressed if it is homozygous. Therefore, the yellow pod plant has homozygous recessive genotype.

A test cross is conducted by the botanist to determine whether the green pod plant is heterozygous or homozygous by crossing it with a yellow pod plant (homozygous recessive).

If any of the offspring plants exhibit recessive traits i.e. yellow pods, it means the parent green pod plant is heterozygous but if all the offspring plants show phenotypic dominant traits i.e green pod, it means the parent green pod plant is homozygous.