Hey guys, it's Metacosis Perfectionatus, where medicine makes perfect sense. Let's continue our genetics section in the biology playlist. Today we'll talk about Gregor Mendel's law of genetics, the first law of segregation, and the second law of independent assortment.
This is my biology playlist. Please watch these videos in order. We talked about this in the previous video.
If you haven't watched it, please go back and revisit it before continuing. Recall the difference between penetrance. and expressivity. Expressivity could be constant, everybody is the same, or variable, where some people have no manifestation or no symptoms, others have mild symptoms, some have moderate symptoms, some have very severe symptoms.
Example here is a disease known as neurofibromatosis. It's called neuro because it affects the brain. Fibroma are tumors usually found on the skin, and osis means condition. So it's a condition that affects your nervous system, and your skin.
These definitions were also discussed in the previous video. Please pause and review. Let's go. The first parent is capital T, capital T. Dominant and homozygous.
The second parent is small t, small t. Recessive and homozygous. Now let's match.
You take the first one from here with the first one from here. And then the first one from here with the second from here. And then you do the exact same thing with the second gamete.
The first with the first. and then the first with the second. And you get these. As you see, all of them are heterozygous.
But since the capital T dominates over the small t, all of them are what? Tall individuals. 100% of the offspring will be tall, like the dominant parent. If you don't want to do it this way, you can use the Punnett square. Gregor Mendel's Law.
What's up, Greg? How are you doing? Listen, my son, and you shall hear of the laws and tenets which I pulled out of my rear.
First law, aka the law of segregation. What is that? Well, each gene may have alternative forms. I know, the alternative is the allele. A L with the L.
One from mommy, one from daddy, right? Exactly. And then suppose that this is your daddy. Okay.
Having a cell with 46 chromosomes, like a spermatogonium. If you want this to divide two sperms, you'll find. N and N. One allele goes to this gamete, the other allele goes to the other gamete. One sperm, here's the other sperm, i.e. the two alleles segregated, separated from each other.
When did that happen? During meiosis. Which phase of meiosis? N phase 1, the phase of disjunction and non-disjunction. Hi, Miracosis, what if the two alleles are different?
One of them will be dominant, i.e. fully expressing the characteristic. into the phenotype. The other will be totally silent, phenotypically speaking, and this is the recessive one.
The second law is the law of independent assortment. Sorry that I misspelled independent. And what does that mean? The inheritance of one gene is independent, not affected by the inheritance of the other gene. Why not?
Because it depends. If you are here, you will cross, but if you are out here, you will not cross. So there is no way to know whether two genes will cross. with each other or will get separated from each other, which means the inheritance of one gene is not affected by the inheritance of the other gene, because we have no idea of knowing who's going to cross over and who one will not.
A very important key concept is when did this happen? Well, it happened in prophase 1 of meiosis, where we had the tetrad and the crossing over and then the recombination. Very important.
So the first law, is by anaphase 1, but the second law is through prophase 1. Big difference. By the way, I have a video about meiosis here on the channel. Please watch that video to learn more.
Let me just remind you that this is meiosis. You see prophase 1? Yeah, which explains the second law of Mendel's, the law of independent assortment. You see this?
This is anaphase 1, where we are segregating. So this is the first law of Mendel. the law of segregation.
It is very important to understand that this happened during prophase I of meiosis, and this is responsible for the second law of Mendel, the law of independent assortment. And again, here are the steps of meiosis I, which were discussed before. Please pause and review.
Prophase I is recombination. This is the second law of Mendel, but the disjunction and a phase I is the disjunction. separation, segregation. So this is the first law of Mendel. Ana phase 1 explains the first law, but pro phase 1 explains the second law.
And that's about it. Please pause and review. Don't forget that both laws increase genetic diversity, which increase the ability of the organism to adapt. If you like this video, you'll enjoy my renal physiology course on my website www.medicosusperfectionaries.com.
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