4
YR and Yr
a hypothesis of getting an offspring with 3:1 ratio Mendel have found that only independent assortment works because independent assortment could predict all of the phenotypic appearances for example, 1) when two true-breading peas cross YYRR*yyrr "Y=yellow, y=green", "R=round, r=wrinkled" 2) all of their offsprings in the First Generation will be YyRr, then when those also cross YyRr*YyRr 3)the result in Second Generation will be in a ratio of 3:1 and the phenotype will be 25% YYRR "yellow-round" 50% YyRr "yellow-round" 25% yyrr "green-wrinkled" Which after all cannot be true because some of the other possible phynotypes are not shown such as Yyrr "yellow-wrinkled" or yyRr "green-round" That's why Mendel thought that independent assortment represents wider and phenotypes Resource from: Biology author:Campbell.Reece, 8th edition thanks
Using a Punnett square, you can calculate the genotype and phenotype of two dihybrid plants. For example, if you have two heterozygous individuals for two dominant traits (we'll pretend the genotype is YyRr), put them into a Punnett square, and you'll get these results: YYRR: 1, YYRr: 2, YYrr: 1 YyRR: 2, YyRr: 4, Yyrr: 2 yyRR: 1, yyRr: 2, yyrr: 1 Phenotypes expressed: Dominant for both traits: 9/16 Dominant for trait 1: 3/16 Dominant for trait 2: 3/16 Recessive for both traits: 1/16 Therefore, the ratio would be 9:3:3:1
1:3:1 3:1 9:3:3:1 4:1