Cells

[loveangel]

so its really possible that the cats and the dogs can breed??? i can't believe it, though if its true well i suppose there's an explanation behind all of these things.

[Dr.Stein]

so its really possible that the cats and the dogs can breed??? i can't believe it, though if its true well i suppose there's an explanation behind all of these things.

Just, watch "the evidence" I provided in the previous page

[Darby]

The "breeding capability" definition is maybe 40 years out-of-date. It turns out that there are many species that can interbreed.

The current best definition (but it only applies to gendered sexual reproducers) kind of lets the organisms themselves define the species: a species is a group that, under natural conditions, only breeds within that particular group.

Lions and tigers can interbreed, but under natural conditions they don't (or didn't, back when their ranges overlapped significantly).

[alextemplet]

That is an interesting definition, but I wonder how biologists define species in asexual organisms.

[Dr.Stein]

Is there any species that cannot reproduce sexually at all? I think they have a potential to do sexual reproduction but the asexual one is much more better Well, I do not know much about microorganisms, they might not able to reproduce sexually..

[sachin]

Is there any species that cannot reproduce sexually at all? I think they have a potential to do sexual reproduction but the asexual one is much more better Well, I do not know much about microorganisms, they might not able to reproduce sexually..

Microorganism are also capable sexual reproduction.(Conjugation process)

Read about F+ and F- factor in bacteria. Check out here.

http://home.comcast.net/~john.kimball1/BiologyPages/A/Avery.html

[Mr Joe]

based on the Glossary of Term in Cellular Biology book, primitive cells refer to prokaryotic cells.

so......does that mean ALL prokaryotic cells can be called "primitive cells" ?

[sachin]

Because they have primitive type of body phisiology.

[Darby]

There are many asexual species, mostly microorganisms, both prokaryote and eukaryote (sex in amebas and flagellates is rare). The definition of species is much fuzzier for them - basically the "old" definition depending upon sets of distinctive characteristics.

One advantage here is that much can be written about "strains" of organisms without having to say that a new species has arisen, which has political ramifications that bench scientists would rather avoid.

The bottom line here is that the real world doesn't care that humans like neat labels - whatever way you swing a definition, there will be plenty of exceptions to deal with.

[Azedenkae]

**note** Most facts/sources from Biology 7th Edition

Reproductive Barriers:

2 species from the same genus can produce fertile offspring if they can cross this barriers:

Prezygotic (Before the zygote developes):

*Note* The first three hinders the attempt to mate at all, the 4th and 5th is even after 2 species can mate, the reasons why the zygorte can't develope and finally the last 3 is after the zygote developes into actual organisms, they might still not be fertile viable offsprings.

1.) Habitat Isolation

2 species may live in different habitats even though they're near each other, therefore encounters could be rare.

E.g. Two species of garter snakes in the genus Thamnophis, although closely related, does not breed (usually) because one lives mainly in the water, whilst the other on land, and doesn't venture into each other's territories a lot.

2.) Temporal Isolation

For example, species might mate at different times of the year, maybe one in late summer the other in late winter, so they don't meet.

3.) Behavioural Isolation

Due to specific courtship rituals, 2 species might not mate.

Some species of birds, although really closely related, cannot mate, because they might have different courtship rituals that prevent them from wanting to mate with each other.

(After mating)

4.) Mechanical Isolation

Morphological differences can prevent successful mating.

For example, 2 very closely related plants might have different pollinators due to different plant colours which attracts different types of bees, therefore they cannot mate.

5.) Gametic Isolation

The sperm cannot fuse with the egg.

This might be because the specific type of sperm cannot survive in the reproductory system of the egg's owner, so it cannot fuse, or due to different mechanisms, the sperm just cannot fuse with the egg.

(If the zygote does form)

6.) Reduced Hybrid Viability

The genes from the parents might fight each other, making the hybrid develope abnormally due to different genes expressing in different cells of the same body.

7.) Reduced Hybrid Fertility

The chromosome number might be different, or the structure might be too different.

The most famous case:

Horse x Donkey = Mule (I had to fight myself vigorously to stop myself from posting the other name for a mule)

8.) Hybrid Breakdown

Even when the hybrid can mate and produce offsprings, the next gen might not due to some sort of error.

9.) Nothing!

If those barriers are overcame, 2 species can mate to form a viable, fertile offspring.

In other words, a hybrid that is basically a new species that can interbreed to form new individuals with the new specie's characteristic that can also breed to form more of the new species.

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So the case of cats and dogs, I think a lot of them don't have different courtship rituals and such (being house pets, so its post-mating that is the problem.

I'm not sure whether the sperm and egg can fuse though. Anyone know?