Altered DNA?

Here's a question/remark I've heard over the years on occasion.


The owner of a certain dog breed - let's say a German Shepherd just to get an example - chooses not to spay the dog and instead breed her. Because, while she hasn't done any preliminary screening for major known genetic diseases, we ARE after all, facing a dog shortage! Oh yeah and she's cute and sweet. 


Anyhow, the unspayed dog lives with an UNNEUTERED Pit Bull. Guess what happens? Oh they thought they kept them apart long enough but no..


So, now facing whelping (which they've never dealt with), they bring her in for an exam and some advice. In the process of discussing this with them, they express their desire to eventually get PUREBRED German Shepherd pups. 


The question is:  Will it ruin that now? Now that's mated with a dog that's NOT a German Shepherd? 


??????


Since when does mating/breeding/becoming pregnant BY a certain breed change the DNA of the mother?? It's like they think her uterus is someone laced with cells of NON BREED of CHOICE dog now. I don't get it. If you (in this case you are a white female) become pregnant by a Chinese guy one time, had his baby, then 3 yrs later met a Hispanic man and had a baby with him, would baby number 2 be Chinese?? AT all?? Um..you know the answer right???