CBSE Class 10 Answered

In crossing over, if 2 or more traits (say of height and colour) are involved, their factors i.e. genes assort independently, irrespective of the combinations present in the parents. In other words, each one of the pair of contrasting characters will coexist with either of another paired type. For example, in a cross between a pea plant having yellow round seedswith another pure pea plant having green wrinkled seeds, Mendel found that the colour of the seed is in no way tied to the shape of the seed. Due to this independent assortment, we get the ratio 9:3:3:1.

The factors controlling a particular trait separate from each other during gamete formation, hence gamete is always pure as far as contrasting characters are concerned.