class 10 biology notes

 1. The Monohybrid Cross (Single Trait): -                                                                                                                                                            • Mendel first looked at how a single trait, like height, was inherited.                                                                                               

• The Cross: He crossed a "pure" Tall plant (TT) with a "pure" Short plant (tt).                                                                                • The F1 Generation: All offspring were Tall.                                                                                                                                                there were "no halfway characteristics"—meaning no medium-height plants.                                                                     This proved that Tallness is the dominant trait.                                                                                                                                           • The F2 Generation: When he let the F1 plants self-pollinate, the "Short" trait reappeared.                                                    He found that 1/4 (25%) were short and 3/4 (75%) were tall.                                                                                                                  • Conclusion: This created the famous 3:1 ratio, showing that traits are carried as "factors" (genes) that don't disappear even if they are hidden. 

 2. The Dihybrid Cross (Two Traits): -

• Mendel first looked at how two traits, like height and shape, was inherited. 

 . • The Cross: He crossed plants with two different characteristics: Tall plants with round seeds (TTRR) and short plants with Wrinkled seeds (ttrr).                                                                                                                                                        • The F1 Generation: All plants were Tall and Round.                                                                                                                                     • The F2 Generation: When these were self-pollinated, the offspring showed "new combinations" that didn't exist in the parents, such as Tall-Wrinkled and Short-Round plants.                                                                                                 • Conclusion: This resulted in a 9:3:3:1 ratio, proving the Law of Independent Inheritance—the gene for height and the gene for seed shape are inherited separately.