What is a Recessive Gene? Oct 14, 2022 | by Donor Nexus

In this video, we explain recessive genes for egg donors using the Punnett Square. If you prefer text, we have the video transcribed for you below. 

What is a Recessive Gene?

Remember in science class when you learned about the Punnett Square? The teacher likely used the example of what eye color the child could inherit from their parents. For example, if one of your parents had blue eyes and the other had brown, you have a 50% chance of either having brown or blue eyes based on the Punnett Square.

The little b is a receive gene and the big B is a dominant gene. When a big B is present, that means how likely the child will have brown eyes.

Genetic Carrier Screening for Egg Donors

The same method is used when an egg donor is screened for what genes they carry. Multiple tests can be used to screen your genes, such as Invitae, SEMA4, Myriad, and Horizon.

You and the sperm provider will be screened using the same kit to ensure that you do not carry the same recessive genes. 

If you participate in an egg banking cycle for our frozen egg bank, you will be screened for 289 genes using an Invitae spit kit. It takes two to three weeks to get your results back.

For example, some genes that are screened for are Tay Sachs Disease and Cystic Fibrosis. 

If your results come back positive for any of the genes screened, it doesn’t mean that you have the disorder or the disease. It just means that you are a carrier of the recessive gene

Here is a Punnett Square that demonstrates if an egg and sperm donor both carry a recessive gene for Cystic Fibrosis. 

There would be a 25% chance that the child would be unaffected and would not be a carrier of the gene.

There would be a 50% chance that the child is also a carrier of the gene.

There would be a 25% chance that the child would have Cystic Fibrosis. 

This is why the clinic determines an egg donor is not genetically compatible if they carry the same recessive gene as the sperm provider. They don’t want to risk the child being affected by the gene.

Empowering You With Insights Into Your Genetics 

What’s great about being an egg donor is that you get to learn all this information for free. You can use this knowledge in the future if you ever decide to have your own child.

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