Question

In a plant, red colour of the fruit is dominant over yellow colour. When these two pure bred varieties are crossed, the $F_2$ progeny have

• A. All plants with red colored fruits
• B. 50% of plants with red fruits and 50% with yellow fruits
• C. 75% of plants with red fruits and 25% with yellow fruits
• D. 25% of plants with yellow fruits and 50% with red fruits.

Answer 1

The correct option is C

75% of plants with red fruits and 25% with yellow fruits

The genotypes of the pure-bred varieties could be considered to be RR (red colour) and rr (yellow colour). The $F_1$ hybrid for these would be Rr (red colour). Now when this $F_1$ hybrid (Rr) is self-fertilized, the following Punnett square explains the possible combinations that could arise.

In this cross, the $F_2$ progeny would show a 3:1 phenotypic ratio. That is both RR and Rr giving rise to red coloured fruits and only rr giving rise to yellow coloured fruit. Hence $75\%$ of the plants produce red fruits and $25\%$ of the plants produce yellow fruits.