# Interesting Cases of Genes

## Pleiotropy and Lethal Alleles

Pleiotropy is the concept of one gene affecting multiple characteristics. On the other hand, when an allele makes some genes nonfunctional, or causes them to take on an abnormal, harmful activity, then there is a good chance the allele is lethal. To delve deeper into this concept, read [this article](https://www.khanacademy.org/science/biology/classical-genetics/variations-on-mendelian-genetics/a/pleiotropy-lethal-alleles-and-sex-linkage), and return here afterward.

## Polygenic Inheritance and Environmental Effects

Human features like height, eye color, and hair color come in lots of slightly different forms because they are controlled by many genes, each of which contributes some amount to the overall phenotype. This is known as polygenic inheritance. Human phenotypes—and phenotypes of other organisms—also vary because they are affected by the environment. Read [this article](https://www.khanacademy.org/science/biology/classical-genetics/variations-on-mendelian-genetics/a/polygenic-inheritance-and-environmental-effects) about the topic, and return here afterward.

## Gene Environment Interaction

Not only do genes and environment affect our behavior, but their effect is also dependent on each other. Watch the video below to delve deeper into the topic.

{% embed url="<https://youtu.be/sMyZO9YDlk8>" %}

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