Question

The violet color of a flower is dominant over white color. Pure lines of violet-flowered plant and white-flowered plant were crossed (cross I). In another cross (cross II), the obtained progeny was crossed with the parent plant bearing white flowers. Which type of cross can cross II be considered or classified as?

• A. Monohybrid cross only
• B. Reciprocal cross only
• C. Back cross only
• D. Both monohybrid and back cross

Answer 1

The correct option is D Both monohybrid and back cross

In the given question, the dominant and the recessive traits have been mentioned clearly. We can also conclude that only one character (flower colour) is under consideration in the cross I mentioned in the question. Hence, cross I is a monohybrid cross carried out for a particular character.

A reciprocal cross is one in which the traits expressed by the male and female parents in the original cross are switched. Reciprocal cross is a relative term, which can be considered only with respect to another cross. In the question, no such switching of sex of parental traits is mentioned. So, neither cross I nor cross II is a reciprocal cross.

A back cross is one in which the F${}_1$ progeny obtained from a respective cross is made to cross with one of the parents. Cross II is a back cross. Since only one character is under consideration, cross II can also be considered as a monohybrid cross. So, cross II is both a monohybrid cross as well as a back cross.