Which genetic cross would exhibit a phenotypic ratio of 9:3:3:1?

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Multiple Choice

Which genetic cross would exhibit a phenotypic ratio of 9:3:3:1?

The phenotypic ratio of 9:3:3:1 is characteristic of a dihybrid cross, which involves two traits that assort independently. Specifically, this ratio arises when both parents are heterozygous for two traits. In the correct choice, both parents are represented as SsYy, meaning they are heterozygous for two different traits (S for one trait and Y for another). When these two parents are crossed, the offspring can exhibit four different phenotypes, resulting in the well-known 9:3:3:1 ratio. This breakdown occurs as follows: - 9 individuals will display both dominant traits (SSYY, SSYy, SsYY, or SsYy) - 3 individuals will display the dominant trait from the first gene and the recessive trait from the second (SSyy or Ssyy) - 3 individuals will show the recessive trait from the first gene and the dominant trait from the second (ssYY or ssYy) - 1 individual will display both recessive traits (ssyy) This distribution happens because of the independent assortment of alleles according to Mendel's laws. The other options do not produce the 9:3:3:

The phenotypic ratio of 9:3:3:1 is characteristic of a dihybrid cross, which involves two traits that assort independently. Specifically, this ratio arises when both parents are heterozygous for two traits.

In the correct choice, both parents are represented as SsYy, meaning they are heterozygous for two different traits (S for one trait and Y for another). When these two parents are crossed, the offspring can exhibit four different phenotypes, resulting in the well-known 9:3:3:1 ratio. This breakdown occurs as follows:

  • 9 individuals will display both dominant traits (SSYY, SSYy, SsYY, or SsYy)

  • 3 individuals will display the dominant trait from the first gene and the recessive trait from the second (SSyy or Ssyy)

  • 3 individuals will show the recessive trait from the first gene and the dominant trait from the second (ssYY or ssYy)

  • 1 individual will display both recessive traits (ssyy)

This distribution happens because of the independent assortment of alleles according to Mendel's laws. The other options do not produce the 9:3:3:

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