Monohybrid Cross (Law of Dominance and Law of Segregation)
Monohybrid cross is a type of hybridization experiment which involves the study of the inheritance of one pair of contrasting character. The alleles of contrasting characters selected in the monohybrid cross will show exact Dominance and Recessive relationships. In Mendel’s classical experiment, he studied seven pairs of contrasting characters and carefully analyzed the segregation of these characters. Based on to the results from Mendel’s monohybrid cross two Mendelian laws were formulated. They were (1) Law of Dominance and (2) Law of Segregation or Law of Purity of Gametes. In this session, we will discuss Mendel’s original monohybrid cross and his conclusions regarding the results he obtained after the cross.
Pisum sativum (source CC Wikipedia)
Mendel selected Pea plants for his hybridization experiments:
Pisum sativum or garden pea was the study material used by Gregor Johann Mendel (the Father of Modern Genetics) for his hybridization experiments. In one of his monohybrid cross, he selected plant height as the character. Plant height in Pisum sativum is controlled by a single gene with two contrasting alleles. The dominant allele of plant height is Tall and he represented it as ‘T’. The recessive allele for the plant height is Dwarf and he represented it as ‘t’. These two phenotypes were morphologically very distinct and can be differentiated very easily.
Procedure of Monohybrid Cross
Ø Mendel selected two pea plants- one a true-breeding (homozygous) tall and the other a true-breeding dwarf.
Ø He generated these true-breeding parent plants by repeated selfing for several generations.
Ø In his experiment, Mendel crossed a homozygous Tall (TT) plant with a homozygous dwarf (tt) plant.
Ø The progenies of the first cross were called as the F1 generation (First filial generation).