How many chromosomes pairs are there in a rat, cow, whale, and human? 
I want the answer for each animal.

Hello pkman,

I quickly found the chromosome for 3 of your 4 mammals, but had
trouble with the whale.

The genomes of the rat (Rattus norvegicus), cow (Bos taurus), and
human (Homo sapiens) are of interest for practical reasons.  The
National Center for Biotechnology Information, a division of the
National Institutes of Health, provides a viewer for the genomes of
these, and several other, animals.  I found the chromosome number for
rat (21), cow (30) and human (23) there.

NCBI's genome viewer:
http://www.ncbi.nlm.nih.gov/mapview/

Rat (Rattus norvegicus)
http://www.ncbi.nlm.nih.gov/mapview/map_search.cgi?chr=rat.inf&query=

Cow (Bos taurus)
http://www.ncbi.nlm.nih.gov/mapview/map_search.cgi?taxid=9913

Human (Homo sapiens)
http://www.ncbi.nlm.nih.gov/mapview/map_search.cgi?chr=hum_chr.inf&query=


The different kinds of whales are classified under the order Cetacea. 
The diversity of whale species, and the lack of a whale genome
project, made finding information on chromosome number more difficult.
 Searching for "whale genome", the I did find a statement by Peter
Folkens of Wheelock College's Whale Net.  He said that some species of
whale have 21 chromosome pairs, and some have 22.  From this I would
infer that the Blue Whale (Balaenoptera musculus) has 22 pairs,
whereas the sperm whale (Physeter macrocephalus) has 21 pairs.

Peter Folkens's answer:
http://whale.wheelock.edu/archives/ask03/0102.html

To understand this, I needed to read more about whale phylogeny:
http://www.cetacea.org/whales.htm
Balaenopteridae (a family of baleen (\x{201C}strainer\x{201D}) whales
eg Blue Whale, Fin Whale)
Balaenidae (eg Bowhead Whale, a type of baleen whale)
Odonotoceti (an order including toothed whales and some dolphins)

I also found one hard journal reference, published in the journal
Nature in 1965.  This article should verify the chromosome number in
the sperm whale; I'll check it at the library later this morning.
Atwood RP, Razavi L. (1965).  "Chromosomes of the sperm whale." 
__Nature.__ 207(994):328-9. PMID: 5886242  No abstract available.


I hope that answers your question!
--neurogeek

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Clarification of Answer by neurogeek-ga on 26 Sep 2005 06:30 PDT

** You asked for the number of PAIRS of chromosomes -- so I answered
in terms of the number of PAIRS.  Usually "chromosome number" refers
to the total number -- for example there the chromosome number for
human is 46.

I hope that is not confusing.

---

Clarification of Answer by neurogeek-ga on 26 Sep 2005 09:44 PDT

The authors in the Nature reference did indeed find 21 chromosome
pairs in a single sperm whale (Physeter eatodon).

Atwood RP, Razavi L. (1965).  "Chromosomes of the sperm whale." 
__Nature.__ 207(994):328-9. PMID: 5886242

I am working on this, I have found the answer for rat (21), cow (30),
and human (23), and have a good lead on the whale.