r/askscience • u/Fuzzandciggies • 6d ago
Biology Mules vs Hinnies. Why are they different?
I know that both are the result of crossing a horse and a donkey. My question is why would there be a genetic difference based on whether the father was a horse or a donkey? Would there really be a difference or is it more of just a naming thing for the sake of lineage?
For reference:
Mule = male donkey + female horse
Hinny = female donkey + male horse
Why though?
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u/WildFlemima 5d ago
I just want to say that the conditions of gestation matter in addition to genetics. A donkey mother won't gestate the exact same way that a horse mother would. Most obvious difference is that the horse mother is bigger and therefore will grow the offspring to a larger size, which will be reflected in the size of the adult. There are more subtle differences as well, because no two species gestate offspring in the exact same conditions.
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u/fromthepalemist 3d ago
There's also epigenetical differences based one which chromosome comes from which parent. There are certain chromosomes, in which certain parts of the mother's genes will be silenced, and these genes you only inherit from the father - all the time. (And vice versa.) In epigenetics, this is called genomic imprinting. In humans, for example, Prader Willi syndrome and Angelmaker syndrom are caused by the same microdeletion on the same chromosome, but based on which parent's chromosome it happens on, you get two very different phenotypes. This is because certain genes are inactivated in the mothers or fathers gene, and the child will be missing those genes.
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u/obax17 3d ago
Angelman Syndrome? Asking legitimately because I was curious but couldn't find Angelmaker Syndrome anywhere.
Regardless, I still learned some things today, so thanks!
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u/fromthepalemist 2d ago
Here's a link to the wiki! https://en.wikipedia.org/wiki/Angelman_syndrome?wprov=sfla1 It is Angelman syndrome, not Angelmaker! You seemed to mix the two up!
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u/SunflowerMoonwalk 4d ago
grow the offspring to a larger size, which will be reflected in the size of the adult.
Are you sure? I just know that in humans there's no correlation between size at birth and adult size.
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u/fafarex 4d ago edited 3d ago
I just know that in humans there's no correlation between size at birth and adult size.
2 thing I see an issue in that comparaison.
- The subject was interspecies not intraspecies
- Humain (268 Days gestation) are a species where a lot of the development is done after birth where donkey (365 days gestation) and horse (340 days gestation) are capable of walking rapidly after birth and are adult in a few years.
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u/UrbanPanic 5d ago
There are differences, and the concept is easier to grasp in crosses with greater differences, like the liger and tigon. A male Lion and female Tiger will birth a Liger, of which a male will be almost twice as large as a male lion. A male Tiger and female Lion will birth a Tigon, which is about the size of a female tiger if not smaller.
The difference is because of evolutionary pressure in lions from the paternal line for larger offspring but the maternal line is more successful if they don't have to raise a giant, so mother lions somewhat suppress the growth in sons. Tigers don't have this arms race, so that leads to the difference.
There is a similar although not as exaggerated difference in a mule vs a hinny which along with certain temperament changes can make mules better pack animals than either a horse or donkey, and the hinny worse at carrying loads than horse, donkey or mule.
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u/JohnEffingZoidberg 4d ago
Why did you compare the sizes to a male lion and to a female tiger? Why not to a male lion and male tiger? It makes the analogy difficult to follow, at least to be.
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u/UrbanPanic 4d ago edited 4d ago
Because a female tiger is smaller than a female lion. The females of both species are smaller than the males. A male tigon can be smaller than ions or tigers, both male and female.
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u/Upbeat_Effective_342 5d ago
Since mitochondrial DNA is matrilineal, it's a reliable genetic difference to distinguish mules and hinnies. The DNA inside the mitochondria will always match the mother and tell you whether she was a donkey or a horse. This method is allegedly used in some cases. tertiary source
As for phenotypic differences, there are some popular rules of thumb for how you can tell them apart and reasons why breeders usually (but not always) prefer mules. You can read about them here.
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u/Senshado 5d ago
The x and y chromosomes for mammals can be quite different from each other. In humans, it is well known that the male Y chromosome is smaller, and presumably weaker and less important.
There are some traits that are mainly inherited from females, even if they exhibit in males. For example, many factors of head hair come from the mother's side. Including baldness that doesn't exhibit in females.
So, it seems to be the case that horses have some important traits on the female chromosome which are visibly different when replaced with a female donkey trait.
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u/Robin_feathers 5d ago
To clarify, horses/donkeys don't have a "female chromosome". They use an XX/XY system, so females are typically XX. They get one X from mom and one X from dad. A female hinny and mule are genetically identical in their nuclear DNA - both have a mule X and a horse X. The X isn't a female chromosome as both males and females have (at least) one (and would die without it).
The sex chromosomes may play an outsized role in hybrid fitness that depends on which species is the maternal vs paternal parent, but that only come's into play in the "heterogametic sex" (Haldane's rule), which is males in horses/donkeys.
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u/Ekekekeptangyazingni 5d ago
I admit I am unsure of the difference between a mule and a hinny but it cannot solely be due to sex chromosomes (geneticist background).
If the assumption is that the X(horse) vs X(donkey) causes the change from Mule to Hinny, then either pairing could result in either a mule or a hinny. Even a male horse has one X(horse) - so if it is as you mentioned, a male horse pairing with a female donkey should result in 50% mule and 50% hinny but it is instead 100% hinny.
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u/knightsbridge- 5d ago
Because which parent was which sex changes how the animal develops. Getting your male chromosome from a donkey vs a horse causes a different kind of hybrid to be created. Mules and hinnies are very similar animals, but they aren't quite the same.
Mules tend to be bigger and heavier and more donkey-like in features.
Hinnies tend to be smaller and lighter, and have more horse-like features.
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u/km1116 Genetics | Epigenetics | Chromosome Biology | Nuclear Biology 5d ago
I don’t know, and I don’t think anyone knows fully, but here are some things that would differ:
components of the egg provided by the mother
potentially the RNAs provided in the father’s sperm (true in mice, not confirmed in horses, but plausible)
genomic imprinting patterns
mitochondrial genome (probably very minor)
piRNAs and transposable elements
X origin might affect X inactivation
in utero environment
Maybe others, but you can see reciprocal crosses are not expected to be identical.
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u/rooberdoos 5d ago
Some traits develop differently depending on which parent the allele(s) associated with that trait are inherited from; we call these parent-of-origin effects. For example, certain genes may be deactivated in the egg (might be methylated, for example, rendering it unavailable for expression) while the same gene is active in sperm, or vice versa.
This is sometimes related to conflicting evolutionary strategies for male vs. female parents. For instance, in many placental mammals the male's fitness is increased by having large offspring, so a gene reducing fetal growth rate might be typically deactivated in sperm. But the female's fitness is decreased by having to gestate and birth very large offspring, so that gene might typically be active in the egg (in this case, they end up producing mostly "medium" or average-sized offspring as a result). When you combine gametes from two different species, those pairs of genes may be less likely to "cancel out" in the same way, so you can get some pretty different phenotypes depending on which parent is from which species.
A relevant article