It's been a long time (high school) since I did any study of biology. I know that in some species the female is larger and/or dominant over the male. I know that in some other species the opposite is true. I know that in some species the male is brightly colored and flamboyant while the female is plain and unremarkable. I can't think of any counter-example, but I'm sure there is one, where the female is colorful while the male is plain. I know that in chickens, there is a way to breed "sex-link" variants where the males and females are easily distinguished based on color (but this is the result of breeding a male of a certain breed with a female of different breed, and the sex-link progeny are not reproducible down the line). I know that chihuahuas and Great Danes were selectively bred from the same common ancestor, and while their size and appearance differs greatly from each other, the size and appearance between males and females within the respective breeds are similar.

Could selective breeding target traits in only one sex? For example could you make a breed of dog where the female is twice the size of a male? Or a breed where the females are brown and the males are black?

 

Very possible.

 

I seem to remember that East Germany was adept at producing very strong and muscular female athletes prior to the collapse of the Soviet Union. Presumably this had little to do with breeding and more to do with steroids and other performance enhancing substances.

 

Very possible.

I know it's possible for fringe cases of extreme conditioning (or conditions) to result in such a physique, in men or women. Humans, or dogs.


I know that it's possible for a female to bigger than most males. I'm asking if it's possible to create a breed where the females are bigger than the males. Where the females being bigger (or more colorful, or a different color, or have shorter legs and bigger feet, or __________ insert trait here) is the rule, not the exception. I want to know if it's possible for selective breeding can be used to target a specific trait in a specific sex (but not the other sex)

 

https://en.wikipedia.org/wiki/Sexual_dimorphism

Natural selection has many species (insects and fish are common examples) where the female can be larger on average so I don't think selective breeding for those traits should be a problem in some types of species. Most mammal species might be an exception for that type of selective breeding.

 

https://en.wikipedia.org/wiki/Sexual_dimorphism
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Natural selection has many species (insects and fish are common examples) where the female can be larger on average so I don't think selective breeding for those traits should be a problem in some types of species. Most mammal species might be an exception for that type of selective breeding.

Why would mammals be an exception? I agree that (to me, uninformed as I am, it seems) it should be no problem to selectively breed for different sex-based traits, but to my knowledge it hasn't been done. The sex-link chickens are the closest thing I know of, and it isn't truly a "breed" where the sex-based traits propagate to the next generation. Having an actual sex-link breed of chickens would be very beneficial to the world. If it were trivial I assume someone would have done it.

 

Why would mammals be an exception? I agree that (to me, uninformed as I am, it seems) it should be no problem to selectively breed for different sex-based traits, but to my knowledge it hasn't been done. The sex-link chickens are the closest thing I know of, and it isn't truly a "breed" where the sex-based traits propagate to the next generation. Having an actual sex-link breed of chickens would be very beneficial to the world. If it were trivial I assume someone would have done it.

For mammals the reproduction process seems to have almost universally made males larger. I don't see this as an accident. IMO it is a refinement of species development at the core reproduction level.

 

For mammals the reproduction process seems to have almost universally made males larger. I don't see this as an accident. IMO is a refinement of species development at the core reproduction.

As is my usual habit, I start a discussion on something I don't know much about, and then go off and do some research as the discussion is ongoing. What I'm reading right now backs up what you just said.

There's natural selection, sexual selection, and what I'll call "unnatural" selection (selective breeding like we do with dogs & livestock). The natural/sexual selection that led to most mammals having a larger male (i assume) took millions of years. Our "unnatural" selection seems to achieve results much faster. How long did it take us to produce mastiffs and teacup poodles from wolves? I doubt we humans underwent any observable evolutionary change whatsoever in that time. If we could create such radically different beings in such a short time, I don't see why we couldn't do the same with a sexually dimophic trait. Maybe it just hasn't been done because it hasn't been a goal. Most of the breeds have been an endeavor with a specific goal in mind (hunting, companionship, pest control, etc) and creating a breed with some whacky sexually dimorphic trait would be selective breeding just for the sake of selective breeding. Except it sure would be handy for chickens... I keep coming back to that.

 

As is my usual habit, I start a discussion on something I don't know much about, and then go off and do some research as the discussion is ongoing. What I'm reading right now backs up what you just said.

There's natural selection, sexual selection, and what I'll call "unnatural" selection (selective breeding like we do with dogs & livestock). The natural/sexual selection that led to most mammals having a larger male (i assume) took millions of years. Our "unnatural" selection seems to achieve results much faster. How long did it take us to produce mastiffs and teacup poodles from wolves? I doubt we humans underwent any observable evolutionary change whatsoever in that time. If we could create such radically different beings in such a short time, I don't see why we couldn't do the same with a sexually dimophic trait. Maybe it just hasn't been done because it hasn't been a goal. Most of the breeds have been an endeavor with a specific goal in mind (hunting, companionship, pest control, etc) and creating a breed with some whacky sexually dimorphic trait would be selective breeding just for the sake of selective breeding. Except it sure would be handy for chickens... I keep coming back to that.

Even with "unnatural" selection it seems some traits like male/female size are somewhat fixed in dogs.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3458007/

The tendency for male-larger sexual size dimorphism (SSD) to scale with body size – a pattern termed Rensch's rule – has been empirically supported in many animal lineages. Nevertheless, its theoretical elucidation is a subject of debate. Here, we exploited the extreme morphological variability of domestic dog (Canis familiaris) to gain insights into evolutionary causes of this rule.

Methodology/Principal Findings
We studied SSD and its allometry among 74 breeds ranging in height from less than 19 cm in Chihuahua to about 84 cm in Irish wolfhound. In total, the dataset included 6,221 individuals. We demonstrate that most dog breeds are male-larger, and SSD in large breeds is comparable to SSD of their wolf ancestor. Among breeds, SSD becomes smaller with decreasing body size. The smallest breeds are nearly monomorphic.

 

So, let's say you want a breed of cats where the males have long tails and short ears, and the females have stubby tails and tall ears. Would it be as simple as mating males with long tails and/or short ears, with females that have short tails and/or tall ears? Because from what I can remember from the elementary biology nearly 2 decades ago, the traits of the offspring would be some lottery combination of the traits of the parents. I don't remember how/where/if the sex comes into it. How would you guide the process to get the traits you want in the sex you want?

 

My guess is that the range of traits that could be sex-linked are limited. Consider that humans have 23 pairs of chromosomes but how many thousands (tens of thousands?) of traits that are determined by them? Since sex is determined by just one of those 23 pairs (and really just 1 of the 46 total chromosomes), the traits that can be strongly sex-linked would seem to be the traits that are determined by that one pair of chromosomes. I would imagine that it is possible for sex to play a role in the expression of traits controlled by other chromosomes since, if nothing else, the hormonal soup that they operate in is strongly sex-dependent, but I would expect the linking to be indirect and harder to control via selective breeding.

 

Yes, selective breeding works. It may take hundreds of generations to see any real significant results. Hence genetic modification by gene splicing greatly speeds up the results. Occasionally a viable and advantageous mutation occurs, most are not viable and far from advantageous even if it survives, and plant and animal scientists are always on the lookout for them. Now they can clone them, very common in the plant world.

 

Expanding on what WBahn's said, my point of view is that (at least in mammals) both sexes share many, many things in common. But an important number of the traits that separate them are kept dormant, and some others are enhanced, by that single pair of chromosomes that determines sex.

Think of this, why do men have nipples, at all? And what are similarities between men and women reproductive organs? There are more than meet the eye.

 

While humans have 23 pairs of chromosomes in our nuclei, there is separate inheritance for mitochondria, which is entirely maternal in humans and most other animals.

Thus, we have mitochondrial traits from the mother and somatic/nuclear traits from both parents. One often hears of "sex-linked" disorders (e.g, color blindness, fragile-X syndrome) that are more prevalent in males. Y-chromosome markers only come from the father. The "Cohen gene" (See: https://en.wikipedia.org/wiki/Y-chromosomal_Aaron) is one example. As an attorney I know said, "You can become Jewish, but you can't become a Jew."

There is no theoretical reason that I know of that selective breeding (allelic selection) could not create more distinctive sexual dimorphism than we currently see.

 

While humans have 23 pairs of chromosomes in our nuclei, there is separate inheritance for mitochondria, which is entirely maternal in humans and most other animals.

Hola @jpanhalt
Could you please elaborate? As you know, non-native with limitations.

 

Hola @jpanhalt
Could you please elaborate? As you know, non-native with limitations.

He's saying mitochondria only comes from the mother.

 

Both the egg (ovum) and sperm have mitochondria. In the egg, they are inside. In the sperm, they are at the junction of the head and tail:

Only the sperm's nucleus enters the egg. Thus, all of one's mitochondria come from the mother.


Mitochondrial DNA is different from nuclear DNA. This describes it:
https://www.nature.com/scitable/topicpage/mtdna-and-mitochondrial-diseases-903/

It's similar to bacterial DNA, which is also circular, and has led to theories that eons ago eukaryotic organisms (organisms with true nuclei in their cells) somehow developed a symbiotic relationship with bacteria, which are prokaryotic as they do not have a true nucleus.

 

At conception, nale and female start out the same. Sex organs are formed fron same parts. How they develop depends on what chromosomes you ended up with (XY or XX or the problematic ones which are actually known genetic conditions). The cheomosomes determine what genes are there and what gets turned on when including various hormones.

As far as traits are concerned, there are a number of sex linked traits, but as far as what is being discussed is concerned that has likely evolved over time through tight association with our evolution as a society and is best suited to our survival needs (at least as far as nature is concerned).

In mammals, sperm is cheap and egg is expensive hence it is males that compete for females or must sell themselves with elaborate displays. That is the crude explanation...

 

Very possible.

 

Ontogeny replicates Phylogeny in Embryonic growth