In this Dihybrid cross, Mendel cross two organism with two contrasting traits Plant with round and yellow seed And one with wrinkled and green seed
This biology question covers important biological concepts and processes. The step-by-step explanation below helps you understand the underlying mechanisms and reasoning.
ScanSolve AI Answer
Let's break down this Dihybrid cross.
First, we define the alleles for the two traits:
For seed shape:
R* = Round (dominant allele)
r* = wrinkled (recessive allele)
For seed color:
Y* = Yellow (dominant allele)
y* = green (recessive allele)
We are crossing a plant with round and yellow seeds with a plant with wrinkled and green seeds. Assuming these are pure-breeding (homozygous) parents, their genotypes will be:
Round and Yellow parent: RRYY*
wrinkled and green parent: rryy*
Step 1: Parental (P) Generation
Parent 1 (P1): RRYY* (Phenotype: Round, Yellow)
Parent 2 (P2): rryy* (Phenotype: wrinkled, green)
Step 2: Gametes from P Generation
P1 (RRYY) can only produce one type of gamete: RY*
P2 (rryy) can only produce one type of gamete: ry*
Step 3: First Filial (F1) Generation
When the gametes from the P generation combine, all offspring in the F1 generation will have the same genotype and phenotype:
Cross: RY × ry*
F1 Genotype: RrYy*
F1 Phenotype: All offspring will be Round, Yellow*.
Step 4: Gametes from F1 Generation
The F1 individuals (RrYy) are dihybrids. According to Mendel's Law of Independent Assortment, they will produce four types of gametes in equal proportions:
RY*
Ry*
rY*
ry*
Step 5: Second Filial (F2) Generation
To find the F2 generation, we cross two F1 individuals (or self-pollinate an F1 individual). We use a Punnett square to show the possible combinations of gametes:
| Gametes | RY | Ry | rY | ry |
| :------ | :--- | :--- | :--- | :--- |
| RY | RRYY | RRYy | RrYY | RrYy |
| Ry | RRYy | RRyy | RrYy | Rryy |
| rY | RrYY | RrYy | rrYY | rrYy |
| ry | RrYy | Rryy | rrYy | rryy |
Step 6: F2 Genotypic and Phenotypic Ratios
F2 Genotypic Ratio:
1 RRYY
2 RRYy
2 RrYY
4 RrYy
1 RRyy
2 Rryy
1 rrYY
2 rrYy
1 rryy
This can be summarized as: 1:2:2:4:1:2:1:2:1
F2 Phenotypic Ratio:
By grouping the genotypes by their phenotypes:
Round, Yellow* (R_Y_): RRYY, RRYy, RrYY, RrYy = 9
Round, green* (R_yy): RRyy, Rryy = 3
wrinkled, Yellow* (rrY_): rrYY, rrYy = 3
wrinkled, green* (rryy): rryy = 1
The classic Mendelian dihybrid phenotypic ratio is: 9 Round, Yellow : 3 Round, green : 3 wrinkled, Yellow : 1 wrinkled, green