Regularities of monohybrid crossing

Mendel’s first law

Monohybrid crossing is the crossing of organisms that differ from each other in one pair of alternative traits.

Mendel studied the patterns of monohybrid crossing of peas.

He considered seven clearly visible alternative properties (white and purple flowers, green and yellow color of seeds, wrinkled and smooth surface of seeds, etc.).

In one of his experiments, Mendel investigated the inheritance of the color of pea seeds when crossing plants with yellow and green seeds. It turned out that in the first generation (F1) all hybrid plants had yellow seeds.

Mendel obtained the same results for each of the seven signs. This is how Mendel’s first law, or the first generation’s law of uniformity, was derived.

When two individuals of pure lines are crossed, differing in one pair of alternative characters, the uniformity of the first generation hybrids is observed.

Mendel’s second law

Mendel self-pollinated the cultivated hybrids of the first generation. The scientist sowed the seeds formed in them again. As a result, he received the next, second generation (F2) hybrids. Mendel examined 8023 peas. Among them, 6022 were yellow, and 2001 were green, which is very close to the ratio of 3: 1.

For other traits, similar results were obtained – in the second generation, splitting according to alternative traits in a ratio of 3: 1 was observed, that is, three quarters of the individuals of the second generation had dominant traits, and one quarter had recessive traits.

This is how Mendel’s second law was established – the law of splitting.

When crossing hybrids of the first generation with each other in the second generation, splitting according to alternative characteristics is observed in a ratio of 3: 1.

The scientist carried out further crossing in order to reveal how inheritance will occur in the third, fourth and subsequent generations. He grew samples using self-pollination.

It was found that plants with recessive traits in subsequent generations produce offspring only with recessive traits.

Plants of the second generation with dominant traits behaved differently. Among them, Mendel found two groups. Some of the individuals gave birth to offspring only with a dominant trait. In the offspring of the other part, splitting was observed: individuals with both dominant and recessive characters appeared in a ratio of 3: 1.