Inheritance

Some physicians are delusional. I hate to break it to you, and no hate to these guys, but y'all can do a little better.

Why am I saying this?

Well, today we are going to be mentioning a physician that "contributed" (no hate) to the fields of heredity and genetics. This guy was named Hippocrates. Ok guys, I'm just hating on him for no reason... he's actually considered one of the most outstanding figures in medicine. But let me hate in peace.

Anyway, this guy thought that there were things called "pangenes" that travel from the body (they leave the body) to the egg and sperm. While this is rather silly, I guess I'll admit that he's pretty formidable. 

But the guy we're actually going to be talking about today is a guy named Gregor Mendell. If you haven't heard of him before, you either live in Antarctica or you're an earth gnome. Just kidding... or am I?

This Mendell guy is quite impressive. He's considered the father of genetics. He became a monk in 1843 and studied pea plants to understand heredity. 

Heredity itself is the transmission of traits from one generation of the next, and genetics is the study of heredity, if you were curious (which you should be)!

In genetics, a character is a heritable feature that various emong individuals. A trait is a variation of a character. In Mendell's case, a character could be considered flower color and a trait of this character could be considered as a purple flower.

As I mentioned in a previous page (I think I mentioned this at least), a gene is unit of inheritance. Variations of genes are known as alleles, and they are denoted by either a lowercase or uppercase letter. For the trait of flower color, two alleles could be P for purple color and p for white color.

Each allele has a dominant and recessive version, labeled by the uppercase and lowercase letters respectively. Different genes are labeled with different letters. When a dominant allele is present, it overshadows the recessive allele, which has no visible impact on the organism. So in the case of flower color, we decided that P (purple) was dominant to p (white). If a plant has a genotype (genetic makeup) of PP, it will have purple flowers. However, if its genotype is Pp, it will also have purple flowers. The only time it will have white flowers is if its makeup is pp. Make sense? Obviously, it is more complicated than this, but this is the basics.

So in summary, genes can be dominant or recessive. There are more options than these, but I will add them to this page if someone wants me to. Please email me at twisha.sharma30@gmail.com if you wish for me to add these to this page.

Let's go check out what Mendell has been doing all this time. While Mendell was alive, he observed the height, flower position, pod color, pod appearance, seed texture, seed color, and flower color of his pea plants. He had a specific way of breeding plants to make sure his results were accurate and not influenced by other factors. In order to breed plants together with non-influenced results, you must first have true-breeding plants (plants that strictly only have either PP or pp. On a separate note, having two of the same alleles means one is homozygous, while the latter means that one is heterozygous). In order to get true-breeding plants, you need to self pollinate them. First, you remove their stamen. Then, you transfer the pollen. Slowly, the carpel you transferred the pollen to will mature into a pod. The seeds from this pod are then planted, growing a true-breeding plant. This process may need to be repeated several times. 

These true-breeding plants were the P generation, or parent generation of the resulting experiment. Their offspring was known as the F1 generation and the offspring of the F1 generation was known as the F2 generation. 

Mendell would breed two P generation true-breeding plants. Let's use our flower color example from earlier to illustrate this. First, Mendell would take one plant with purple flowers and one plant with white flowers and breed them. All the offspring would have purple flowers. However, when he took the offspring in the F1 generation and bred them, 75% of the offspring in the F2 generation would have purple flowers while 25% would have white flowers. How is this so? 

To help explain this, I am going to use a Punnet square to illustrate the way the genes are being passed down.

In the Punnet square to the left, we can see that the purple flower is being bred to the white flower in the parent generation. The purple flower's alleles and the white flower's alleles are shown beside their respective sides. When they are bred, one of each allele is passed down to its offspring. In this case, we have created four Pp plants that are heterozygous. Since the dominant allele always prevails over the recessive one, the flowers are purple. 

Now let's breed the F1 generation together. As we can see, three of the F2 generation flowers have a dominant allele, making them purple. However, one of them two recessive alleles - thus, it is white. The genotypic ratio(ratio of genetic makeup) is 1 PP : 2 Pp : 1 pp. However, the phenotypic ratio (ratio of physical appearance) is 3 purple : 1 white. 


So what can we conclude from this information? Well, several things. I'll tell you about Mendell's conclusions though, so you can hear it from a professional if you don't like me.

I hope you enjoyed this page and all of its contents! I love you guys! Unfortunately, that's all I have for you today. Have an amazing day and I'll see you in the next one! :)