Recessive and dominant genes

[ncrocker]

I think there is a discussion of my question already somewhere, but I can't find it, so, sorry, but I will ask it again!
I remember somewhere in high school or elsewhere, that for instance in simple cases, you get two genes for eye color, one from mom and one from dad. Some eye colors, like blue, come from having two blue-eye recessive genes, one from mom and one from dad. If you get just one blue eye gene and one brown eye gene, then you do not get blue eyes. Thus, they say, some genes are dominant and some recessive. I can't make the jump from the eye color story to the one about getting two copies of ApoE4! Clearly, my first language is not genetics! I hope you know what I am talking about. Thank you! I feel so much better when I understand things. My motto is: when the going gets tough, the tough do research!

[optimize]

some genes are dominant and some recessive. I can't make the jump from the eye color story to the one about getting two copies of ApoE4

Would it help if you learned that human eye color is really dependent on 15 or more different genes, each contributing their influence, nudging the final color? And that eye color can change with age, and environment?

The strict recessive/dominant idea only holds true for some genetic disorders (Mendelian traits), like cystic fibrosis or sickle-cell anemia. Most of the time genes work in more interactive way, like instruments of an orchestra, or players on a soccer team. Each of our two (usually two) gene copies contributes a certain protein or enzyme, and altogether the mix of different genes' output makes the total person.

Some of our gene copies create a lot of a particular protein or enzyme, and some hardly any. Different gene versions can make slightly different variations of protein and enzymes. Sometimes the amount and type they churn out depends on something in the environment, like a food or a pathogen.

The ApoE gene is involved with the transport of fats, and comes in different versions (ApoE2 through ApoE4). It's not a matter of one ApoE type being dominant or recessive, it's more about how much and which variation of protein each type makes.
https://ghr.nlm.nih.gov/gene/APOE and https://www.dietvsdisease.org/apoe4-die ... rs-disease

[slacker]

Beautiful explanation optimize!

[ncrocker]

Thank you optimize! That really helps!

[marthaNH]

I think I might have to clip and save that explanation. Thanks.

[Athena22]

Hi I have been wondering, along the same lines, why if about 30% of the population is 3/4, why the percentage of 4/4s is so small? Unless I’m not doing the math properly, wouldn’t it be more like 7.5% (one fourth of 30%) rather than 1.5%?

[CarrieS]

Hello Athena22
I'm not a gene expert and I don't have an answer to your question above but I DID want to Welcome you to this knowledgeable and caring community. As you tour around the forums, check out Stavia's Primer for some great diet & lifestyle information. You can find it here: viewtopic.php?f=33&t=1418. You can also click on the "spyglass" icon to the left of your name to bring up the Search function, type in a word and bring up any previous threads that may interest you. When you are ready, we'd love to hear more about you in the Our Stories forum.

[NF52]

Hi I have been wondering, along the same lines, why if about 30% of the population is 3/4, why the percentage of 4/4s is so small? Unless I’m not doing the math properly, wouldn’t it be more like 7.5% (one fourth of 30%) rather than 1.5%?

Welcome, Athena22,
Great question! The frequency of ApoE 4/4 varies between groups with different ancestry, but the figure I have usually seen is about 25% of the population having one copy of ApoE 4 (that could be 3/4 or the much less common 2/4). So we could say that theoretically, each person with ApoE 3/4 has a 25% chance of having a child with another person with ApoE 4, and a 75% chance that they will have a child with someone who has no ApoE 4. So the chances of two people having kids and being ApoE 3/4 is .25 x .25. or 12.5% chance of a couple each being ApoE 3/4.
If we think of the possible combinations of 3/4 and 3/4, we get 3/3, 3/4, 4/3 and 4/4. So each couple with ApoE 3/4, with each pregnancy, has a 25% chance of having a child with ApoE 3/3, a 50% chance of having a child with one ApoE 4 allele and a 25% chance of having a child with ApoE 4/4. So the 12.5% of couples who each have ApoE 3/4 now becomes divided by 4 for the likelihood of a child with ApoE 4/4 or 3.1% . And that's if the roll of the dice was absolutely predictable each time. It's not, and many areas of the world have lower percentages of ApoE 4, which means those populations are even less likely to have two 3/4 individuals have children together. What I've seen for most estimates of ApoE 4/4 in a European and European-ancestry population is about 2.2%.
(I don't know about your family, but on one side I have German Catholics who had 11 kids, and on the other English and Irish Catholics who married late, had fewer kids and only one married. Easy to skew the numbers when you're dealing with real people!)

[Karengo]

Hi I have been wondering, along the same lines,

Hello and Welcome to you Athena22!

Thank you for wondering and for sharing your thoughts. It's great to hear from you. While I don't think I can help to shed light on your question, I'm certainly curious and wondering along with you!

We would love to hear more from you. Please feel free to ask questions and see if you can get answers. I think you'll find this community if well-informed and super supportive of each other. I see you've heard about physician member, Stavia's Primer where you'll find a ton of information probably leading to more questions! And whenever you feel inspired, I invite you to share some of your story - while reading about others - here at
Our Stories

Again, wishing you a warm welcome. Thank you for becoming part of our community!

Best