# Difference btwn. mouse and rat? **URL:** \ **Category:** Factual Questions\ **Created:** [March 21, 2004, 8:07pm UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594 "2004-03-21T20:07:51Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![dotchan](https://avatars.discourse-cdn.com/v4/letter/d/9d8465/32.png) [@dotchan](https://boards.straightdope.com/u/dotchan)\ **Post date:** [March 22, 2004, 4:19am UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/21 "2004-03-22T04:19:50Z")
I don’t remember what the V.C.C. biology lab used as part of their semesterly experiment on adaptive behavior, but they were smalish, white, furry, and _really_ friendly with each other. We were joking that they must have been gay until we discovered two litters of squirming, pink babies. Turns out that they weren’t all female after all. But how, exactly, were we supposed to check? The babies and mommies were, IIRC, eventually fed to various pet snakes. ☹ ---
**Author:** ![edwino](https://avatars.discourse-cdn.com/v4/letter/e/35a633/32.png) [@edwino](https://boards.straightdope.com/u/edwino)\ **Post date:** [March 22, 2004, 4:24am UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/22 "2004-03-22T04:24:34Z")
Genetically, rats have 21 chromosomes to the mouse 20. These are not equivalent for the most part – there have been at least 19 large scale rearrangements. The rat genome was sequenced to approximately 6.5x coverage, with 90% of sequence assembled into contigs, by a combination of whole genome shotgun and BAC sequencing. I don’t believe it was finished or completely annotated, though. Total sequence is 2.6 gigabase pairs (Gbps) of the estimated 2.8 GBps of the genome. Mouse was sequenced by Celera and the Mouse Consortium to well over 10x coverage and 96% assembly into contigs, by whole genome shotgun coupled to a tiled BAC sequencing approach. This spans more than 2.4 of the estimated 2.6 Gbps of the genome. There has been a careful finishing and annotation process that has been nearly as intensive as the work given to the human genome project. From [this Science article](http://www.sciencemag.org/cgi/content/full/303/5657/455) (requires subscription): > [@](#): > > About 39% of the _(rat)_ bases are common to all three, and the shared DNA includes about 95% of the regulatory regions and protein-coding DNA for all three species. That’s the core mammalian genome, says Ross Hardison of Pennsylvania State University, University Park. Another 700 million bases are specific to the rat and the mouse and may define rodents. Rat-specific DNA comprises the rest, about 750 million bases. > > Many of the rat’s estimated 26,000 genes–about as many as in mice and humans–are shared with these species. Mice may have up to 1000 more identified genes in common with humans than do rats–perhaps 11,000 in all. Mice and rats appear to have 11,500 that are equivalent, but the genes are often expressed at different times and in different tissues. Further human-rat analyses showed that certain genes in the rat, such as those involved in the immune system, differ from the human versions more than do other genes, such as those involved in the nervous system, suggesting that groups of genes have been subjected to different evolutionary pressures. That means that they are actually pretty different genetically. Compare humans and chimps, which have only 1.4% difference in their DNA, compared to the around 75% (to my rough calculations) shared between mouse and rat. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [March 22, 2004, 8:15am UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/23 "2004-03-22T08:15:39Z")
> [@Phase42](#): > > And of course, we can’t forget to mention ROUS - Rodents Of Unusal Size. > > 😃 I don’t think they exist. ---
**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\ **Post date:** [March 22, 2004, 12:06pm UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/24 "2004-03-22T12:06:52Z")
> [@](#): > > Rats are VERY good mothers. Most of them, anyway. I have a momma with 15 babies right now, and none of them have died (biggest litter I’ve ever had). > . . . > Rats (I assume you meant mice in this context) can eat their babies if they don’t get enough protein. While mice will eat their young under stressed conditions, I would not declare them “bad mothers.” From the other perspective: when mice are _not_ stressed, all the females in a cage (even those that have not yet bred) will take turns “babysitting” a litter of pinkies while the mother takes time out to forage for food. Mothers that give birth within a few days of each other will have their litters in the same place and the mothers appear to nurse whoever wants food until they are weaned. ---
**Author:** ![mischievous](https://avatars.discourse-cdn.com/v4/letter/m/c2a13f/32.png) [@mischievous](https://boards.straightdope.com/u/mischievous)\ **Post date:** [March 22, 2004, 9:33pm UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/25 "2004-03-22T21:33:38Z")
I breed tons of mice in a lab environment, which is a bit different from pet mice, but I thought I’d comment. > [@Silver Serpentine](#): > > (Mice, I think) can eat their babies if they don’t get enough protein. Yes, but if you’re feeding them properly they mostly they don’t. Some strains are more prone to this than others, especially the inbred strains. > [@](#): > > Mice tend to eat each other if they get bored (or something - maybe they just don’t like each other). Adults, not just babies. This seems to be strees/enclosure size related, something I’ve never noticed in my rats. Apparently, they become stressed more easily. Also happens when introducing a new mouse into an established colony. Mice will fight if over crowded. Don’t overcrowd (duh). There is also a relatively rare dominance behavior called “barbering”, where a dominant (female, usually) will chew the fur off the shoulders of others in the cage. I get maybe 3-5 cases of this a year, while taking care of a constantly rotating population averaging ~400 mice. Maybe once a year the barbering female gets out of hand and chews skin, too - but this doesn’t seem to be a deliberate killing. > [@](#): > > Male mice, so they tell me, STINK. Stink like a 10g with 5 rats. This, also, is strain-dependant. > [@](#): > > Apparently they’re not so friendly. Nippy and such. If they’re handled regularly, they aren’t nippy at all. If they haven’t been handled, they get scared. However, they’re really not very bright, and sometimes forget that your fingers aren’t food. They’ll nibble, then let go. Additionally, anyone who’s at all familiar with rodents can tell a mouse from a rat at a glance, even without size cues. Rats are built differently, and most have nude tails. The faces are different too. [rant]It annoys me to no end when we get catalogs for mouse products/services in the lab with cute pictures of fuzzy little mice in cute little poses - except they’re rats. Do these morons think that their customers can’t tell the difference if there is no indication of size? Or do they not know the difference themselves? (Not very encouraging in a mouse services company.)[/rant] yours, mischeivous ---
**Author:** ![mischievous](https://avatars.discourse-cdn.com/v4/letter/m/c2a13f/32.png) [@mischievous](https://boards.straightdope.com/u/mischievous)\ **Post date:** [March 22, 2004, 11:08pm UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/26 "2004-03-22T23:08:41Z")
Upon reflection, I thought I should add that male mice which have mated _do_ fight, and kill, each other. For breeding purposes, single males need to be kept in separate cages for mating, but groups of virgin males can be kept together in a single cage (with no females, obviously). mischievous ---
**Author:** ![Silver\_Serpentine](https://avatars.discourse-cdn.com/v4/letter/s/3be4f8/32.png) [@Silver\_Serpentine](https://boards.straightdope.com/u/Silver_Serpentine)\ **Post date:** [March 23, 2004, 5:18am UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/27 "2004-03-23T05:18:55Z")
Thanks for enlightening me about mice, hehe. I get my information from another forum on feeder rodents for snakes, and those were the examples given to me when I asked if I should breed mice or rats. If I get into corn snakes, I’ll probably have to start breeding mice too, so it’s good to know. And yeah, I meant mice in that one thingy. Oops! Does anyone know if mice get stressed more easily than rats? I’ve read several posts on the other MB about how you should keep mice in a quiet, not high-flow area of the house, but nothing about that for rats. I have my rats in a high-traffic area, and my cats sleep on top of the cages, and I haven’t seen any signs of stress. ---
**Author:** ![cichlidiot](https://avatars.discourse-cdn.com/v4/letter/c/5f9b8f/32.png) [@cichlidiot](https://boards.straightdope.com/u/cichlidiot)\ **Post date:** [March 23, 2004, 7:48am UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/28 "2004-03-23T07:48:27Z")
> [@Silver Serpentine](#): > > Rats are VERY good mothers. Since we’re adding anecdotal evidence, here’s what I’ve noticed. Rats are as good of mothers as mice. The difference I’ve noticed, is that usually, if there’s other adult female rats in with a rat giving birth, at least one rat will generally serve as a “midwife”, in that, she grabs the pinkies as they come, cleans them up, and stuffs them in a corner where they’re “safe”. The only trouble I’ve seen from this, is when the mother is done with labor, sometimes the midwife is a bit reluctant to turn the babies over. Have not noticed this in mice, as often. As far as baby eaters, barring overcrowding, and generally stressful conditions, I’d go with Hamsters (not the Siberian or Chinese), as the main culprits. I’ve watched a mother take her babies and munch them as they come out, on more than one occasion. > [@](#): > > Surprisingly not terribly stinky. I clean my cages whenever I can smell ickiness when I give them food and water, and even tho I have 3 females and 15 babies in one cage, 5 or 6 weanlings in another (for now), and two big males in the other, I only have to clean about ever 2 weeks. I’ve noticed male rats do tend to have a musky scent, as they mature. If you are familiar with ferrets, it’s very similar, just a lot less pungent. I have never noticed this smell with male mice. What I _do_ notice, is that male mice are compulsive at marking territory. In an average week, I took care of anywhere from 25 to 200 mice. Once a week, I would take out everything and disinfect it. Once the water bottle and its holder was replaced (newly disinfected), the male’s one mission, was to squirt that thing until it was covered. It reeked, and consequently so did the cage. > [@](#): > > This seems to be strees/enclosure size related, something I’ve never noticed in my rats. Apparently, they become stressed more easily. Also happens when introducing a new mouse into an established colony. Not true at all, in my experience. I think rats are as easily stressed, or at least, mice are not more easily stressed. I find I am more likely to stress out a mother rat by reaching in to move babies, than with a mouse, and also more likely to get bitten. I’ve seen an entire cage of rats pounce on a newcomer, as often as I’ve seen it happen with mice. > [@](#): > > Apparently they’re not so friendly. Nippy and such. I disagree with this as well. I’d rather have a rat for a pet, but it has nothing to do with nippiness. I’ve found most mice take to flight almost every time when frightened by being handled. Rats unfamiliar with being handled, seem to resort to fighting a lot more often than mice. ---
**Author:** ![peterW](https://avatars.discourse-cdn.com/v4/letter/p/bb73d2/32.png) [@peterW](https://boards.straightdope.com/u/peterW)\ **Post date:** [March 23, 2004, 2:12pm UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/29 "2004-03-23T14:12:51Z")
> [@Phase42](#): > > And of course, we can’t forget to mention ROUS - Rodents Of Unusal Size. > > 😃 I read this in the morning and later in the evening, I managed to finally watch **The Princess Bride**. The figurative light bulb glowed bright that night. A classic line 🙂 ---
**Author:** ![mischievous](https://avatars.discourse-cdn.com/v4/letter/m/c2a13f/32.png) [@mischievous](https://boards.straightdope.com/u/mischievous)\ **Post date:** [March 23, 2004, 11:05pm UTC](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594/30 "2004-03-23T23:05:48Z")
> [@Silver Serpentine](#): > > I have my rats in a high-traffic area, and my cats sleep on top of the cages, and I haven’t seen any signs of stress. I’ve never bred rats, so I can’t compare, but I can tell you for a fact that lab mice haven’t the foggiest clue that cats are predators. I took some to a friend’s house once, and the damn things sniffed around, said hi to the cats, and then **tryed to burrow under the (sitting) cat’s stomach**, presumably because it looked safe and warm. The cat, freaked out by this non-prey behavior, ran off. With regards to baby-eating, I have a little theory (take it with salt). Sometimes baby-eating seems clearly a product of stress and overcrowding, but sometimes it happens with otherwise happy mothers. The mothers do need to eat the placenta and lick the pups clean after they are born, and I think that sometimes they get a little confused as to where they are suppossed to stop eating - they’re not so smart. Second-time mothers almost never eat their litters. I’ve also noticed that putting a piece of paper towel into the cage can be a good predictor of maternal behavior. A unhappy (or non-pregnant) mouse will rip it into large pieces and pile it flat, whereas happy, pregnant mice will completely shred it into microscopic pieces and fluff it all around them into a huge ball they can hide in. YMMV (your mice may vary), of course. mischievous [Previous page](https://boards.straightdope.com/t/difference-btwn-mouse-and-rat/235594.md?page=1)