Okay. So now let's talk about Mendel's Law. Mendel studied pea plants, and he was able to make a bunch of observations, which led him to conclude certain properties and certain laws about inheritance. Some of these properties that he deduced from these pea plant experiments were that there was some type of factor that was important for inheritance, and we now call this factor a gene. And this gene is absolutely necessary for producing a certain trait, such as seed color—yellow or green. This gene comes in two forms, which we now call alleles, and we know that these two forms are yellow and green, as mentioned above. So the alleles come in two forms. One form or allele is dominant to the other. As previously discussed, yellow is the dominant allele, as yellow seeds consistently produce yellow offspring. Green seeds produce green offspring, but since yellow is often present, the green trait is mostly masked by the dominant yellow allele.
Now, Mendel's laws were able to take that information and actually formulate laws that govern genetics. These are super important, and we're going to discuss all three. The last one, the law of independent assortment, is going to get its own chapter, which is great. The first two we're really going to focus on. The first one is the law of segregation, which means that alleles separate during meiosis, the cell division that creates sex cells. Therefore, alleles separate to form gametes, which are sex cells. Each gamete contains a single allele for each trait. It either contains the allele for yellow or green or the dominant or the recessive allele. Gametes only contain one allele, and this principle is the essence of the law of segregation. The law of dominance states that some alleles are dominant and others are recessive. In the examples discussed with Mendel, it's clear that yellow is dominant because it appears frequently, and green is recessive because the only guarantee of obtaining a green-seeded plant is if there is no yellow allele present.
The third law, the law of independent assortment, though more complex and detailed than what we've discussed so far, essentially states that genes for different traits segregate into gametes independently. This is about considering more than one trait, such as color and shape of seeds, which separate independently into sex cells. It's not predetermined that all yellow seeds must be round; they can segregate into gametes completely independently. If you're confused about this, that's okay, as this law will be elaborated on in its own chapter. However, it's crucial to understand now the law of segregation, how there's one allele per sex cell, and the law of dominance, that one allele is more dominant.
Here's another example involving a cross of white and red flowers. The notation in this image is slightly different than what you would normally see. But looking at this, we first revisit the law of segregation, which reminds us there will be one allele per gamete. As observed in the organisms, each has two alleles, but during the formation of gametes, these alleles are separated out into single alleles combined to create the next generation. The law of dominance then informs us that one of these alleles will be more dominant than the other. Looking at the presence of red and white flowers, it is clear that the red allele is more dominant because there are considerably more red than white flowers. These are the first two laws that Mendel proposed. With that, let's now move on.