HOW TO MAKE A PUNNET SQUARE WITH STEPS , AND FIND ITS GENOTYPIC AND PHENOTYPIC RATIO OF BOTH MONOHYBRID AND DIHYBRID CROOS EACH. THANX

Asked by Pushpanjali | 26th Jul, 2016, 09:38: PM

Expert Answer:

Important step is you place all the gametes formed in the self-cross in the punette square table.

Once your punette table is ready, first count offspring for phenotype and write the phenotypic ratio.

Then count similar genotypes and write the genotypic ratio.

Monohybrid Cross:

In this monohybrid cross, if we count offspring by their phenotype, we get 3 tall and 1 dwarf plant. Hence, its phenotypic ratio is 3:1.

If we check the genotype of the offspring then, we have 1 TT (homozygous tall), 2 Tt (heterozygous tall) and 1 tt (homozygous dwarf). Hence, its genotypic ratio is 1:2:1.

 

Dihybrid Cross:

In the above dihybrid cross, if count offspring by their phenotype, we get 9 plants with round and yellow seeds, 3 plants with round green seeds, 3 plants with wrinkled yellow seeds and 1 plant with wrinkled green seed. Hence, its phenotypic ratio is 9:3:3:1.

Genotypically, there are 9 different types of plant combinations, RRYY, RrYy, Rryy, rryy, RRYy, rrYy, Rryy, Rryy and rrYY. The genotypic ratio is 1 : 4 : 1 : 1 : 1: 2 : 2 : 2 : 2.

Answered by Hemangi Binny | 28th Jul, 2016, 10:16: AM