The correct answer is the law of segregation or the law of purity of gamete.
Meiosis results into the formation of gametes. The gametes are always pure for a particular trait because each gamete carries either the dominant or the recessive factor but not both as we find in F1 individuals. This follows the 'principle of segregation', the law proposed by Mendel. This law is also called 'law of purity of gametes'. The ratio 3:1 in F2 generation of a monohybrid cross suggests that alleles are segregated and the test cross confirmed it.
