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

Biology

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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

  1. Parental (P) Generation

    • Parent 1 (P1): RRYY (Phenotype: Round, Yellow)
    • Parent 2 (P2): rryy (Phenotype: wrinkled, green)

  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

  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.

  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

  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:

    GametesRYRyrYry
    RYRRYYRRYyRrYYRrYy
    RyRRYyRRyyRrYyRryy
    rYRrYYRrYyrrYYrrYy
    ryRrYyRryyrrYyrryy

  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
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