High School

II. Monohybrid Cross

Widow's peak (W) is dominant over a straight hairline (w). Perform a cross using a Punnett square. Give the genotypic and phenotypic ratio of the following crosses:

1. WW x WW
2. WW x Ww
3. Ww x Ww

Answer :

To solve this problem, we'll use a Punnett square to determine the genotypic and phenotypic ratios of the offspring from each cross. Widow's peak (W) is dominant over a straight hairline (w).

  1. Cross: WW x WW

    • Parental Genotypes: WW and WW
    • Punnett Square:
      [tex]\begin{array}{c|c|c}
      & W & W \\ \hline
      W & WW & WW \\ \hline
      W & WW & WW \\
      \end{array}[/tex]
    • Genotypic Ratio: 100% WW
    • Phenotypic Ratio: 100% Widow's peak

  2. Cross: WW x Ww

    • Parental Genotypes: WW and Ww
    • Punnett Square:
      [tex]\begin{array}{c|c|c}
      & W & W \\ \hline
      W & WW & WW \\ \hline
      w & Ww & Ww \\
      \end{array}[/tex]
    • Genotypic Ratio: 50% WW, 50% Ww
    • Phenotypic Ratio: 100% Widow's peak

  3. Cross: Ww x Ww

    • Parental Genotypes: Ww and Ww
    • Punnett Square:
      [tex]\begin{array}{c|c|c}
      & W & w \\ \hline
      W & WW & Ww \\ \hline
      w & Ww & ww \\
      \end{array}[/tex]
    • Genotypic Ratio: 25% WW, 50% Ww, 25% ww
    • Phenotypic Ratio: 75% Widow's peak, 25% Straight hairline

The Punnett square helps predict the likelihood of different genotypes and phenotypes of the offspring based on the parent's alleles in a genetic cross.

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