This is a science question.  Chromosomes come in pairs and are numbered.  So which is the proper way to say both chromosomes of a particular pair are normal?
Examples:
Both chromosome 9s are normal
Both chromosomes 9 are normal.
It seems to me that the first option is correct because the second option makes the adjective, chromosome, plural.

It seems to me that the first option is correct because the second option makes the adjective, chromosome, plural.

I would be tempted to think that it’s the 9 there that’s an adjective, not chromosome.  Anyway, I think, as you say, the first option is right, since you have a compound noun chromosome 9 and when that is the case, normally the second term takes the s, not the first (cf. apple pies, bunkerbed, etc.).

I could be squarely wrong, though.  :)

Brazilian dude

Not my native language, but for Swedish I would unhesitatingly start from ‘both chromosomes’ and then append the 9 without any modification.

"Chromosome 9" is the subject.

But, what about "chromosomes 9 and 10"?

e.g., Delta 98. ("Delta 98s", not "Deltas 98")

But, if Oldsmobile came out with a new model called the "Delta 99", would one say,

"Those new Oldsmobile Delta 98 and Delta 99 are roomy".

Like,

"Those new Chevrolet Impala and Impala SS are fast".

Are these sentences correct? They sound kind of awkward to me. In fact, I’m confused now.

VB

[quote author=Brazilian_dude link=board=grammar;num=1142108052;start=0#1 date=03/11/06 at 16:51:45]
I would be tempted to think that it’s the 9 there that’s an adjective, not chromosome.  Anyway, I think, as you say, the first option is right, since you have a compound noun chromosome 9 and when that is the case, normally the second term takes the s, not the first (cf. apple pies, bunkerbed, etc.).

I could be squarely wrong, though.  :)

Brazilian dude

I think chromosome must take the plural because it is the most basic part of the compound noun. There’s probably a more technical word for that, but what I mean is that ‘chromosome 9’ is a kind of chromosome, not a kind of nine. In ‘apple pies’ the second term takes the plural, not because it is the second term, but because you’re talking about pies and not apples.

You’ve convinced me, Spiff.  I’m on your side now.

Brazilian dude

Couldn’t you also say both ninth chromosomes and avoid the whole question?

Apparently it is not uncommon to phrase it as chromosome 9s, though, based on my informal Google survey.

-Tim