Why are hybrid animals different depending on which parent is from which species ?
In: Biology
Well, at least partly it’s because hinnies are gestated in donkeys and mules are gestated in horses. Since mules are smaller than horses, a hinny will usually be smaller than a mule to reflect the mother’s size and nutrients it got in utero and through breastfeeding. Plus a hinny is raised by donkeys and a mule is raised by horses, so their behavior will reflect how they were raised, a bit. They do look very similar and it’s hard to tell the difference by just appearance. But there are also certain genetic differences–hinnies have donkey mitochondrial DNA (mtDNA) and mules have horse mtDNA. You only get mtDNA from your mother and there are certain mtDNA differences between the species. Likewise hinnies have horse y-chromosomes and mules have donkey y-chromosomes, so whatever genes are being controlled by y-chromosomes are going to reflect the species it came from.
Sometimes there are differences in terms of genes that are activated in females vs. males. Like in the liger tigon example given by someone else, the liger is huge–much bigger than either lions or tigers. this is because the male lion has a gene that encourages growth in offspring, while the female lion has a gene that suppresses that growth, resulting in the lions we see today. But when you breed a male lion with a female tiger to get a liger, you get the gene from the male to increase growth but tiger females don’t have the gene that suppresses growth meaning you get far more growth in a liger than you get in a lion or a tiger. Likewise the tigon is a lot smaller than a liger, because the female lion passes on genes to suppress growth, without having the gene to increase growth from the male lion.
And finally, there’s something called genomic imprinting: some genes are expressed differently depending upon whether they were inherited from the mother or the father. This isn’t hugely well understood yet, but basically there’s a process whereby a gene’s expression is chemically altered based on whether it came from a mother or a father. The classic example of this is Prader-Willi Syndrome and Angelman Syndrome. Basically, in humans, if a particular spot on chromosome 15 is deleted in the genes inherited from one’s father, then the child will have Prader-Willi Syndrome. If that same spot is deleted in the genes inherited from the mother, the child will have Angelman Syndrome.
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