$A$ cross was carried out between a pure-bred tall pea plant and a pure-bred dwarf pea plant,and $F_{1}$ progeny was obtained. Later,the $F_{1}$ progeny was selfed to obtain $F_{2}$ progeny. Answer the following questions:
$(a)$ What is the phenotype of the $F_{1}$ progeny and why?
$(b)$ Give the phenotypic ratio of the $F_{2}$ progeny.
$(c)$ Why is the $F_{2}$ progeny different from the $F_{1}$ progeny?

(N/A) The phenotype of the $F_{1}$ progeny is tall. This is because the allele for tallness $(T)$ is dominant over the allele for dwarfness $(t)$. In the $F_{1}$ generation,all plants have the genotype $Tt$,where the dominant trait masks the expression of the recessive trait.
$(b)$ The phenotypic ratio of the $F_{2}$ progeny is $3:1$ (Tall : Dwarf).
$(c)$ The $F_{2}$ progeny is different from the $F_{1}$ progeny because,in the $F_{2}$ generation,the recessive alleles segregate and pair up in the homozygous condition $(tt)$,allowing the dwarf phenotype to be expressed,which was hidden in the $F_{1}$ generation.