What are the parental genotypes that resulted in this Punnett square?

Question

BlackTom AI · Accepted Answer

We need to examine the given Punnett square and infer the parental genotypes that produced it.
Option 1: YyRr and YyRr
This pair represents two heterozygotes for both genes (one copy of Y from one parent and y from the other, and one copy of R from one parent and r from the other). A dihybrid cross with YyRr x YyRr would yield all combinations from Y/y and R/r assortments, matching the four different allele combinations shown in the Punnett square (YR, Yr, yR, yr) in the gametes. This is consistent with the observed variety of offspring genotypes in the grid.
Option 2: YYRR and yyrr
This pair would be a cross between a homozygous dominant (YYRR) and a homozygous recessive (yyrr) parent. All offspring would be heterozygous for both genes (YyRr) and would produce a uniform genotype in the offspring, not the four distinct combinations seen in the Punnett square. Therefore, this does not fit the diagram.
Option 3: YYRR and YyRr
Crossing YYRR with YyRr would yield offspring that are either YYRR, YYRr, YyRR, or YyRr, but not the full set of four distinct gamete combinations across the grid in the same balanced way as shown. While some genotypes would appear, the parental gametes would be biased toward consistent parental alleles (both Y and R from one parent), which is not represented by the diverse gamete labels in the diagram. This option is inconsistent with the four equally represented gamete types shown as inputs to the grid.
Option 4: YrRr and yyrr
This pairing mixes a dihybrid but with one parent carrying Yr and the other carrying yyrr. The expected offspring would show a different pattern of genotype combinations (not the clean YR, Yr, yR, yr gamete set equally depicted). The presence of a parent with yyrr would not produce the correct balanced assortment of Y/y and R/r alleles across all four columns and rows as seen. Hence, this is not a match for the diagram.
In summary, Option 1 aligns with a dihybrid cross between two heterozygotes for both genes, producing the four equally probable gamete types (YR, Yr, yR, yr) and the corresponding offspring genotypes observed in the Punnett square. The other options imply parental genotypes that would generate biased or uniform offspring patterns that do not fit the illustrated grid.

What are the parental genotypes that resulted in this Punnett square?

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