Mum: O+
Dad: B+
Me: O-
In: 673
Dad’s genes must be – O+ and O-. Mom’s genes – at least one B gene, possibly two. If two B genes, then it’s B+ and B-. If it’s just one B gene, if it’s B+, then the other gene is O-, and if it’s B-, then it’s O+. The genes for blood type and rhesus factor code separately.
This assumes you are the biological child of these people.
From my basic of basic understanding of genetics. Your Dad and moms DNA are made up of your grand parents and maybe they had a trait for O-. Or maybe your test has a mistake, which happens rarely. Or maybe there is more to the story. In the most likely case you may just be lucky and we’re given some distant trait.
RHD+ is a dominant trait. This means that if you have one + and one – copy of the RHD gene, you will always be RHD+. If two such people with mixed genetics have a kid, there’s about a 25% chance that their kid inherits both – copies which makes them RHD-.
Dominant and recessive genes.
For example, the gene for Brown eyes is dominant, the gene for blue eyes is recessive. So if I get the brown-eye gene from one parent and the blue-eye gene from the other, I’m going to have brown eyes, because the brown-eye gene is dominant and ‘wins’ over the blue-eye gene.
But, I still have the blue-eye gene that I can pass along to my children. So let’s say my wife also has both the blue-eye and brown-eye gene. She’ll also have brown eyes because, again, the brown-eye gene is dominant… but if our child gets the blue-eye gene from me *and* gets the blue eye gene from my partner, they’d have blue eyes despite the fact neither me or my wife has blue eyes.
Basically, both your parents have the rhD- gene which is recessive, they both passed that on to you
You get one copy of the rhD gene from your mom and one from your dad. The combination of those two genes results in your rhD expression.
The rhD+ gene is dominant, so if **either** of the two genes in the pair is +, then you will express as positive.
The genetic makeup of both of your parents is the same – they both have one gene that is positive and one that is negative. This results in them both expressing as rhD+.
They both passed to you their copy of the rhD- gene. Since both of your genes are rhD-, you express as rhD-
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Same thing with the blood types. A and B are dominant genes, while O is not. Your mum has two copies of the O gene, which means she expresses as O. Your dad has one copy of the B gene and one copy of the O gene, meaning he expresses as B. The both passed on to you an O gene, giving you two O genes, so you express as O just like your mum.