Assertion: A geneticist crossed a pea plant having violet flowers with a pea plant with white flowers, he got all violet flowers in first generation. Reason: White colour gene is not passed on to next generation.

Dear Student 

​​​​​​Both assertions and reason are correct. But reason is not correct explanation of the statement as in this case the violet color is a dominant trait and white might be present in genotype but its is not visible.

Regards