Two yellow-flowered hybrid plants each carrying a recessive factor for flowers with green colour were crossed…

Analyze the question: Two yellow-flowered plants are hybrids (heterozygous), and each carries a recessive factor for green flowers. We need the proportion of offspring with green flowers.

Concept: This is a monohybrid cross (Mendel's first law). Yellow is dominant (Y) and green is recessive (y). A hybrid has the genotype Yy. Green flowers appear only when the plant is homozygous recessive (yy).

Solution:

Cross: Yy × Yy

| | Y | y | |---|---|---| | Y | YY | Yy | | y | Yy | yy |

• Genotypic ratio: 1 YY : 2 Yy : 1 yy
• Phenotypic ratio: 3 yellow : 1 green

Only the yy offspring are green, so the proportion is 1 in 4 (25%).

Why the other options are wrong:

• A (2 in 2) would mean all offspring are green, which is impossible here.
• B (1 in 3) confuses the 3:1 ratio with the fraction of green offspring. Green is 1 out of 4 total, not 1 out of 3.
• D (1 in 5) does not come from any Mendelian monohybrid ratio.

Exam tip: When two hybrids (heterozygotes) are crossed, remember 3:1 for phenotype. The recessive trait is always 1 out of 4 of the total offspring. Don't mix up "3 : 1" (a ratio of parts) with "1 in 4" (a fraction of the whole).