Haploid for Protein Genes?

[IrishTwins]

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Just listening to the examkrackers audio osmosis, Disc 8, Track "The Gene." They say,

"Now do each of our cells contain one and only one copy of each gene?"

"That depends. Prokaryotes have only one copy of each gene. For most proteins, eukaroytes also have only one copy. But for some genes, such as genes coding for tRNA, rRNA and especially those coding for heterochromatin, the eukaryotic cell contains multiple copies."

"So for most proteins, one significant mutation and the cell loses the protein completely?"

"Right."

This one of those things that, if its true, I'm going to feel like I just stepped into the twilight zone. 😱 How could I manage to do well in cell biology, genetics, etc and not know that for most proteins we only have one copy / are haploid? How can this even be possible? The only thing I can come up with is that most proteins are coded by mitochondrial DNA which is maternal?

Any insight?

 

[RogueUnicorn]

they might initially mean "single copy" genes, of which there is only one copy per haplotype... that being said yea, one significant mutation ==> complete protein loss is utterly incorrect