# Blood Types and Genetics **URL:** \ **Category:** Factual Questions\ **Created:** [July 17, 2003, 8:47pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227 "2003-07-17T20:47:30Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![biddee](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@biddee](https://boards.straightdope.com/u/biddee)\ **Post date:** [July 17, 2003, 8:47pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/1 "2003-07-17T20:47:30Z")
Is it possible for two A blood type parents to have an O child? And if so, how does that work. I had always assumed that an A- mother and an A+ father have two possibities when the child is born, A- or A+. I read a post on a pregnancy message board talking about rhesus factors where one woman said that she was A- and hubby was A+ and they have two O+ daughter and one A+ son. Does her hubby need to worry that the first two daughters aren’t his? Thanks:confused: ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [July 17, 2003, 8:55pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/2 "2003-07-17T20:55:21Z")
Yes. The “O” gene is recessive. So a person with type A or B can also have an “O” gene from the other parent. ---
**Author:** ![Earl\_Snake-Hips\_Tucker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/earl_snake-hips_tucker/32/3269_2.png) [@Earl\_Snake-Hips\_Tucker](https://boards.straightdope.com/u/Earl_Snake-Hips_Tucker)\ **Post date:** [July 17, 2003, 8:56pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/3 "2003-07-17T20:56:41Z")
This also means that _both_ parents have to be carrying the recessive “O” gene. ---
**Author:** ![Dogface](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@Dogface](https://boards.straightdope.com/u/Dogface)\ **Post date:** [July 17, 2003, 8:56pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/4 "2003-07-17T20:56:48Z")
- and - refer to Rh type. Somebody who is Rh- is homozygous recessive. Rh+ could be homozygous dominant or heterozygous, so a + and - mating could produce either + or - children. Blood type genotypes vs. phenotypes: Genotype Phenotype aa A a0 A bb B b0 B ab AB 00 O Blood typing is an extremely simple genetic system. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 17, 2003, 8:58pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/5 "2003-07-17T20:58:27Z")
A person with type A blood has one type A gene and one type O gene. A person with type B blood has one B gene and one O gene. Thus two people with type A or B blood (or one of each) have a 25% chance of having a child with type O blood (two O genes). A mixed couple with an A parent and a B parent also have a 25% chance of having an AB child (one A gene and one B gene). ---
**Author:** ![biddee](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@biddee](https://boards.straightdope.com/u/biddee)\ **Post date:** [July 17, 2003, 8:58pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/6 "2003-07-17T20:58:31Z")
Thank you…that’s good to know…so if the O gene is recessive and my bf is O+ and I know for a fact that both my parents were A, does that mean I’ll have an A baby? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 17, 2003, 9:02pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/7 "2003-07-17T21:02:23Z")
> [@](#): > > \*Originally posted by biddee \* > \*\*Thank you…that’s good to know…so if the O gene is recessive and my bf is O+ and I know for a fact that both my parents were A, does that mean I’ll have an A baby? \*\* Knowing only that both your parents were A type means that you are either A or O type. If you are O, you and your boyfriend have a 100% chance of having an O baby. If you are A, you and he have a 50% chance of having an O baby. ---
**Author:** ![Annie-Xmas](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@Annie-Xmas](https://boards.straightdope.com/u/Annie-Xmas)\ **Post date:** [July 17, 2003, 9:06pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/8 "2003-07-17T21:06:03Z")
If one of your A parents was O recessive, you could be carrying the O recessive gene. If you are the chances only 1/4 for an A child (with a recessive O gene), vs. 3/4 for an O child. ---
**Author:** ![biddee](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@biddee](https://boards.straightdope.com/u/biddee)\ **Post date:** [July 17, 2003, 9:07pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/9 "2003-07-17T21:07:48Z")
Q.E.D. I am A, sorry, forgot to put that in my post. So even though my parents were both A, that doesn’t mean that I am AA, I could be AO? I think I’m getting it now…sorry to be so dense…thank you for your time. ---
**Author:** ![Annie-Xmas](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@Annie-Xmas](https://boards.straightdope.com/u/Annie-Xmas)\ **Post date:** [July 17, 2003, 9:21pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/10 "2003-07-17T21:21:57Z")
Yes. One or both of your parents could be AO, and you could have gotten the recessive gene. If you’re O, you know you are OO (no A or B genes), or if you’re AB, you know you are AB (no O genes). A’s and B’s could have recessive O’s. In the above example, it shoukld be 50/50 of either A or O. My mistake, the four options are AO, OO, AO, or AO. :smack: ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 17, 2003, 9:44pm UTC](https://boards.straightdope.com/t/blood-types-and-genetics/189227/11 "2003-07-17T21:44:17Z")
> [@](#): > > \*Originally posted by biddee \* > \*\*Q.E.D. I am A, sorry, forgot to put that in my post. So even though my parents were both A, that doesn’t mean that I am AA, I could be AO? I think I’m getting it now…sorry to be so dense…thank you for your time. \*\* To elaborate a little more: Since you don’t know your parents’ genotype, but only their phenotype (A), several possibilities exist: If they are both genotype AA, then you would have a 100% chance of being AA. If one is AA and the other AO, then you would have a 50% chance of being AA and 50% of being AO. If both are AO, then you have a 25% chance of being AA, 50% of being AO, and 25% of being OO. (Of course, since you already know you are A phenotype, in this scenario you actually have a 33.3% chance of being AA and 66.7% chance of being AO).