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AP®︎/College Biology
Species
Taxonomy comes to life through the exploration of species, defined as groups of animals that can interbreed to produce fertile offspring. Examples of species include lions, tigers, and horses. Hybrids are the offspring of different species, which are usually infertile. Examples of hybrids include mules and ligers. Created by Sal Khan.
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- Is the term 'species' also used interchangeably with 'breed'? It seems that I regularly see articles declaring 'New species of butterfly/frog/flower discovered!' . Did anyone really test those butterflies for their reproductive capacity?(81 votes)
- "Breed" is another term for subspecies, usually applied to animals. In plants, the term "cultivar" or "variety" is often used instead.
This video illustrates the Biological Species Concept ( a species is a group of organisms that interbreed and produce fertile offspring) and well as obliquely referring to the Morphological Species Concept (species are groups of organisms that share similar features - usually physical structures).
There are problems with the BSC, for example the definition does not work well for species that reproduce asexually. It also does not work well for hybridization, when two species interbreed AND produce fertile offspring, as is the case with many birds and plants.
There are other concepts of species, such as the ecological species concept (occupying a distinct ecological niche) or the phylogenetic species concept (group of organisms that share a distinct ancestry).(51 votes)
- why do lions and tigers mate?(17 votes)
- I would venture to guess that they don't naturally mate in the wild, but that humans put them up to it when in captivity.(19 votes)
- Why can't mules have babies? I just don't get it.(4 votes)
- Mules are a mix between a horse and a donkey. After this reproduction (I won't be too specific here) a mule inherits 63 chromosome. To reproduce sexually an organism must give 1/2 of its reproductive chromosomes to its offspring, and 63 cannot be divided in half to equal a whole number. Therefore it cannot reproduce sexually because it does not have the proper number of chromosomes.(60 votes)
- i dont understand...how do donkeys and horses or, tiger and lion mate? they would not do that normally would they? they are just not the same type!!!
(12 votes)- In the wild, the species you mentioned don't actually interbreed. When two animals cannot produce fertile offspring as illustrated in these two examples, they are separate species.(13 votes)
- Could a liger breed with a lion?(4 votes)
- Yes! This is an actual thing that has happened.
https://en.wikipedia.org/wiki/Liliger
Even hybrids can create fertile offspring, despite what you may have heard.(19 votes)
- Why is the offspring between a lion and tiger going to look predictably different depending on whether the mother or father is the the lion or visa versa. Doesn't offspring get half the mother's and father's genes in any case. Shouldn't offspring look mostly the same whether or not the father was a lion or tiger?(7 votes)
- This is a good question!
It is true that the ligers and tigons both get roughly§ half their genes from from each parent.
However, some genes behave differently depending on the sex of the parent they came from and this is at least partially responsible for the differences between these hybrids.
This phenomenon is known as imprinting (genomic or epigenetic imprinting) and you can start to learn more here:
https://learn.genetics.utah.edu/content/epigenetics/imprinting/
Does that help?
§Note: Not exactly half since mitochondria are almost always exclusively maternally transmitted. In addition, Y chromosomes are smaller than X chromosomes so male offspring will get more nuclear genes from their mother than their father.(5 votes)
- Can mule mate with other mule and produce offspring?(3 votes)
- A horse has 64 chromosomes and a donkey has 62. A mule inherits 32 horse chromosomes from mom and 31 donkey chromosomes from dad, for a total of 63 chromosomes.
The offspring of a male horse and a female donkey is a hinny.
There is decent correlation between the gene location on the chromosomes of a donkey and a horse but it is not perfect and there is an unmatched chromosome from the horse.
The normal cell replication process of mitosis can do the duplication of the chromosomes since it is done on a chromosome by chromosome basis.
In the process of meiosis where the creation of the sex cells there is a phase where the matching pairs of chromosomes are put together and processed as a pair and because of the gene location mismatches and it can't handle the single unpaired chromosome so the creation of sex cells will normally fail.
Without sex cells being produced a mule is sterile and can't produce offspring.(7 votes)
- What "species" are humans classified as?(2 votes)
- The genus is "homo" and the species is "sapiens"(3 votes)
- Does this apply for other species too? Like say, for a shark and an orca to interbreed? Will their offspring be fertile? Or does the "different species interbreeding generally means the offspring is NOT FERTILE" rule count? PS, sorry if the "different....FERTILE" bit was confusing.(2 votes)
- No, not all species are defined by ability to produce fertile offspring. There really is no clear biological definition about what separates one species from another. Some species are distinguished by their breeding separation from another group. While they could interbreed with another species and produce fertile offspring, for whatever reason, they simply don't interbreed and are considered different species.(4 votes)
- how are animals of diffrent species drawn to mate with each other?(3 votes)
- Different species have different methods of attracting mates. One of the more common means is to release a chemical called a pheromone. While there are many kinds of pheromones, one kind of pheromone is the sex pheromone. The release of such a sex pheromone attracts potential mates.
If you meant what would cause a member of one species to mate with a member of another species, that is very rare in nature, but not unheardof. Typically, you might expect to see that if two different species have highly similar pheromones and thus some members of one species might be confused into mating with the other species (this would typically happen with closely related species). Also, the lack of potential mates during breeding season sometimes causes cross-species mating.(3 votes)
Video transcript
We humans like to get
our heads around all of the complexity around
us by classifying things. And you could imagine
there's no more obvious thing to classify than all of the
living things around us, than all of the life
that surrounds us. So what I want to
start talking about is, how do we classify all
of the life around us? And this is more often
generally referred to taxonomy. But the most basic
question you have when you look at
all the life around, you start to see similarities
between some of these living things. You see, obviously this
thing right over here is more similar to the
things that look like it, than it does to the grass
behind it, or to that tree. And so we start saying, well
maybe I should group this thing right over here into a group
with other things like it. And that very most
building block of how we classify all of
the living things around us, is putting them into
buckets called species. So for example, this is
one particular animal, but we see other animals
that seem to look like it, and so we say they're all
part of the species of lions. And this animal,
it's one animal, and there's other animals
that have stripes, but some might be fatter,
or taller, or skinnier, or whatever else,
darker, or lighter, but we say they're
similar enough, that we call them all tigers. We call all the animals,
even though they might be a little bit bigger,
or skinnier, or fatter, or lighter, or darker, we
call all of them-- they look similar to this thing
right over here-- we would call this a donkey. We would call the
things that we think are like this animal
right here, a horse. Now, that might seem like a
pretty straightforward way to think about it. Oh, everything that looks kind
of like this character right here is a lion,
anything that looks kind of like this character
right here is a tiger. But that, by itself, is not
a good enough definition for a species. Things that look like
each other or things that act like each other,
because what we'll see is that there's some
things that could be very different, at least
in and how they look or act, but are actually
closely related. And we'll talk about what it
means to be closely related. And then we can see things that
look very similar, that they have similar structures or
they have similar behavior, like for example bats and
birds, but they are actually all very, very
distantly related. So we need a more exact
definition for species than just things that
look like each other, or just things that
act like each other. And so the most typical
definition for species are animals that can interbreed. And when we say
interbreed, literally they can produce offspring
with each other, and the offspring are fertile. Which means that the offspring
can then further have babies, that they're not
sterile, that they're capable of breeding
with other animals and producing more offspring. And to show an example of this,
this right here is a male lion. You find a male lion
and a female lioness and most of the time they will
be able to have offspring, and those offspring
can go and mate with other lions or lionesses,
depending on their sex, and then they can
have viable offspring. So it seems to work out
pretty well for lions. Same thing is true of tigers. Now, it does turn
out that if you get a male lion and a female
tigress they can breed. They can breed and they
can produce offspring. And their offspring--
which was made famous by Napoleon Dynamite, he
was kind of fascinated by, these are kind of
fascinating animals. Their offspring
is called a liger. You get a male lion
breeding with a female tiger you produce a liger,
which is a hybrid, it's a cross between
a lion and a tiger. And they're fascinating animals. They're actually larger
than either lions or tigers. They are the largest
cats that we know of. But these ligers cannot be
referred as a separate species. Or you can't say
that lions and tigers are the same species,
because even though they are able to interbreed, their
offspring, for the most part, is not fertile, is not
able to produce offspring. There have been one off
stories about ligers being mated with either
a lion or a tiger, but those are one off stories. In general, ligers
can't interbreed. And in general, this
combination isn't going to produce offspring
that can keep interbreeding or that are fertile. So that's why we say
that lions and tigers are different species. And that liger, we wouldn't even
call it as a species at all. We would actually call it a
hybrid between two species. Now the same thing is
true-- and actually you might be asking
yourself, well, this was a male lion and
a female tigress, what if we went the
other way around? What if we had a female
lioness and a male tiger? In that case, you would
produce something else called a tiglon or a tiglon,
I actually don't know how to pronounce that. And that is a
different hybrid that has slightly different
properties than a liger. I encourage you to look
up what a tiglon is. Similarly, you give
me a male donkey. And donkeys are clearly
a species by themselves, because if you give me a male
donkey and a female donkey they can reproduce, produce
another donkey, and then that donkey can
mate with other donkeys to produce more
and more donkeys. So not only can a donkey
interbreed with another donkey, but that product,
that child donkey, can keep interbreeding
with other donkeys. Similarly, horses, they
can interbreed and produce fertile offspring. But if you give me a male
donkey and a female horse they can mate and they
can produce a mule. But once again, like
the ligers, mules are not, at least
as far as I know, mules they're not fertile. Mules cannot produce
further offspring. They cannot interbreed
with each other. And because, even though
donkeys and horses can breed and produce mules, their
offspring aren't fertile. We don't consider
donkeys and horses part of the same species. And we would consider mules,
like a liger or a tiglon, we would consider them a hybrid. So these are all hybrids,
or we would call cross. In general, the
word hybrid is used when you have two things,
two different types that are somehow coming together,
somehow having a combination. And once again, like the
case with the tiglon, you might say,
well, what if I had a female donkey
and a male horse? And then you would
actually produce something called a hinny, which
isn't as common as a mule. And people like to
use mules, they're actually very good work
animals because they have some of the good properties
of both donkeys and horses. Hinnies are less common, but
once again, it is possible. And they have different
properties than mules. And I do want to
emphasize this idea. Because when we started
off we just tried to think about, well, how
can we classify things? And we said, hey, maybe things
that look and act similar, we can call a species. And maybe things that
look and act different, we shouldn't call them species. But I want to show you a
very typical case, one that's really all around us all the
time, where this definition-- animals that can interbreed
and the offspring are fertile-- really does seem to become much,
much more important than just some notion of animals
that look alike or animals that act the same. And the best example
of that is with dogs. As I said, this is a very
typical species here, because dogs-- and I just
took a sample of some of the different types
of breeds of dogs-- they can look very,
very different. It's obvious, look at the
difference between these dogs. For example, this
little chihuahua here and this dog
right over here. Obviously, they're
size-wise, their look, and even how they act are much,
much more different than maybe how this donkey would act
relative to this horse, or how this lion would act
relative to this tigress. And they obviously
look very different, they have completely
different sizes, but these two things
actually can interbreed-- although for these
two in particular, it seems like the mechanics
would get kind of difficult-- but assuming they get over
the mechanical hurdles they could interbreed and
produce fertile offspring. Same for these two characters,
same for these two characters over here. And because of that, even
though all the different breeds of dogs-- and most
of this is really due to humans' doings
of trying to breed for a specific traits-- even
though they look so different, and even though they act so
different, because they can interbreed, and they could
produce fertile offspring, we consider all of
these things to be members of the same species.