Question

explain with the help of illustration diagram mendel monohybrid cross.

Answer 1

Monohybrid cross - The cross in which only one pair of contrasting or alternative traits are involved.
Mendel's law of segregation is explained by monohybrid cross.
Exp- Pure tall Pure dwarf
parental generation- TT tt
gametes for F1 - T t
F1 progeny- Tt (hybrid tall)
self cross - Tt (hybrid) x Tt (hybrid)
gametes foe F2- T ,t T ,t
F2 progeny - TT, Tt, Tt, tt
So,here pure tall(TT)= 1
impure or hybrid tall(Tt)= 2
pure dwarf(tt)= 1
genotypic ratio= 1:2:1
phenotypic ratio=3:1

Answer 2

A cross between pure breeding tall (TT) and dwarf (tt) varieties gives all heterozygous tall (Tt) progeny in F1

generation. Selfing of F1 hybrid gives tall and dwarf F2

progeny in 3: 1 ratio respectively. Since allele for tallness (T) is dominant over that of dwarfism (t); heterozygous dominant genotype (Tt) gives "tall" phenotype and dwarfism is masked from being expressed. Both homozygous dominant (TT) and heterozygous dominant (Tt) exhibit "tall" phenotype while homozygous recessive genotype gives dwarf phenotype; hence phenotypic ratio is 3 tall: 1 dwarf but the genotypic ratio is 1 TT: 2 Tt: 1 tt.

Parent generation TT x tt

F1 generation Tt

Selfing Tt x Tt

F2 generation TT Tt Tt tt