$A$ woman having blood group $B$ marries a man having blood group $A$ and they have four offspring. Two children have blood group $O$,one has blood group $B$,and one has blood group $AB$. Now,answer the following:
$(i)$ Which blood group is dominant?
$(ii)$ Which blood group is recessive?
$(iii)$ What are the genotypes of the parents?
$(iv)$ Show the possible genotypes and phenotypes of the offspring.

(N/A) $(i)$ Both blood group $A$ and blood group $B$ are dominant (codominant).
$(ii)$ Blood group $O$ is recessive.
$(iii)$ Since the offspring include blood group $O$ $(OO)$,both parents must carry the $O$ allele. Therefore,the father's genotype is $AO$ and the mother's genotype is $BO$.
$(iv)$ The cross between $AO$ and $BO$ results in the following genotypes and phenotypes for the offspring:
- $AB$ (Phenotype: $AB$)
- $AO$ (Phenotype: $A$)
- $BO$ (Phenotype: $B$)
- $OO$ (Phenotype: $O$)
This cross explains the presence of all four blood groups in the offspring.