Why did Mendel test one trait at a time?

Answer 1

Mendel tested one trait at a time so he would be able to eliminate variables. The purpose of his experiment in general was to determine the trends and patterns in inheritance, and so he had be sure he studying only one variable at a time, to understand it well. Specifically, he examined one trait at a time with self-pollinating pea plants, of which there were only two color varieties: purple and white. Before now, there was no chance of white flower's seed having previously been fertilized by a purple flower. He also chose to use peas because they spawn a new generation quickly and produce a large number of offspring. So during the first generation of his pure purple flower and pure white flower crossing, all of the offspring produced purple flowers. Because his subjects were chosen only for the reason of color, and did not differ in other ways, he knew, what would later become known as, the purple-color allele was dominant. It was previously believed that the two colors would "blend" together, producing a pale purple color. So it would make sense that the trait for producing a white flower was lost, and that the flowers would be purple from now on, right? When the this generation self-fertilized, however, there was 3:1 ratio of offspring. 3 purple flowers and 1 white flower. Mendel now had a basis for determining the law of segregation. Later, after performing other various two-option-single-trait experiments such as seed color and wrinkled vs. smooth, he discovered traits were inherited singly, and thus the law of independent assortment was born. Mendel's experiments gave in beautifully to ratios of inherited traits and the ability to determine what traits the offspring would possess as more traits were mixed. If he had tested multiple traits at one time, even unintentionally, his results could have been skewed and even meaningless.

Answer 2

Mendel tested one trait at a time in his experiments because it allowed him to clearly observe the inheritance pattern of that specific trait without the complexity of multiple traits interacting simultaneously. This approach helped him establish the principles of inheritance and develop his laws of inheritance.