Understanding Epistasis: How Genes Interact

Epistasis is the way genes work together. Sometimes, one gene can hide or change how another gene shows itself. This is important for figuring out how some genetic disorders are passed down.

Types of Epistasis

1. Recessive Epistasis:

   • In this type, if there are two hidden (recessive) versions of a gene at one spot, they can cover up the effects of genes at another spot.
   • For example, in albinism, the hidden gene for skin color (called A) can cover up another gene (called B) that is supposed to help make color.

2. Dominant Epistasis:

   • Here, a strong (dominant) version of a gene can hide the effects of other genes.
   • For instance, in squash plants, the strong white fruit color gene (called W) can cover up the green color gene (called G) from another spot. This leads to a specific mix of colors in the offspring.

How it Affects Genetic Disorders

Epistasis is important in understanding certain genetic disorders, like cystic fibrosis and sickle cell disease.

• Cystic Fibrosis:

  • People with this condition usually have changes in a gene called CFTR.
  • Other helper genes can change how bad the disease is, showing how genes can interact with each other.

• Sickle Cell Disease:

  • A change in the HBB gene can lead to different symptoms, depending on other genes. This shows that not all inheritance follows the traditional patterns we expect.

Some Facts to Know

• About 1 in 25 people of European descent have the cystic fibrosis gene.
• Sickle cell disease occurs in about 1 in 365 African American babies.

In conclusion, epistasis makes understanding how traits are passed down more complex. It helps explain how different genes influence the appearance of genetic disorders and how they can work together in surprising ways.