of tall and dwarf plants obtained by Mendel was tall and dwarf. External expression of a particular trait is known as phenotype. So the phenotypic ratio is : . In the F generation different types were obtained: Tall Homozygous – TT (Pure) – Tall Heterozygous – Tt – Dwarf Homozygous – tt – So the genotypic ratio : : .
A genotype is the genetic constitution of an organism Mendel’s Interpretation on Monohybrid cross Based on these observations it was confirmed by Mendel that ‘factors’ are passed on from one generation to another, now refered to as genes . Tallness and Dwarfness are determined by a pair of contrasting factors , tall plant possess a pair of factors (represented by T- taking the first letter of the dominant character) and a plant is dwarf because it possess factors for dwarfness (represented as t- recessive character). These factors occur Genetics in pairs and may be alike as in pure breeding tall plants (TT) and dwarf plants (tt). This is referred to as homozygous .
If they are unlike (Tt) they are referred to as heterozygous . . Two factors making up a pair of contrasting characters are called alleles. Phenotypic expression of alleles are called allelomorphs .
One member of each pair is contributed by one parent. . When two factors for alternative expression of a trait are brought together by fertilization. The character which expresses itself is called dominant (Tallness) condition and that which is masked is called recessive condition (Dwarfness) .
. The factors are always pure and when gametes are formed, the unit factors segregate so that each gamete gets one of the two alternative factors. It means that factors for tallness(T) and dwarfness(t) are separate entities and in a gamete either T or t is present. When F hybrids are self crossed the two entities separate and then unite independently, forming tall and dwarf plants.
. Dihybrid Cross- Inheritance Two Genes and Law of Independent Assortment Dihybrid cross involves the inheritance of two pairs