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Biology Question 121 – NEET-UG 2024

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A pink flowered Snapdragon plant was crossed with a red flowered Snapdragon plant. What type of phenotype/s is/are expected in the progeny?

Recall the concept of incomplete dominance, where the heterozygous genotype results in an intermediate phenotype, as seen in Snapdragon flower color.

Step 1: Identify the Genetic Principle✦ Active

Flower color in Snapdragon plants exhibits incomplete dominance. This means that the heterozygous genotype produces an intermediate phenotype (pink) between the two homozygous phenotypes (red and white).

Step 2: Determine Parental Genotypes○ Expand

Let's denote the alleles: R for red color and W for white color. According to incomplete dominance:

- Red flowered plant genotype: RR

- White flowered plant genotype: WW

- Pink flowered plant genotype: RW (heterozygous)

The cross is between a pink flowered plant (RW) and a red flowered plant (RR). The gametes produced by the pink plant are R and W. The gametes produced by the red plant are R and R.

💡 Teacher's Secret Hint

Remember that in incomplete dominance, the heterozygous phenotype is distinct from both homozygous phenotypes.

Step 3: Perform the Cross and Predict Progeny Phenotypes○ Expand

Using a Punnett square for the cross RW×RR:

RRRRRRRWRWRW

The possible genotypes in the progeny are RR and RW. The phenotypic ratio will be:

- RR: Red flowered plants (50%)

- RW: Pink flowered plants (50%)

Therefore, the expected phenotypes in the progeny are Red flowered plants and Pink flowered plants.

💡 Teacher's Secret Hint

Always clearly identify the genotypes and their corresponding phenotypes based on the inheritance pattern.

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