Just pondering how this works and thought I would ask your thoughts. Do you think when you breed a stallion to a mare, the genes are processed so that they are combined to reach a median or the resulting foals combines the genes independently and their traits are not actually a combination of the genes meshed together but each separately expressed in the foal’s makeup. If you are trying to shorten a back or tone done a sensitive/hot mare – are you thinking the foal will get a back or temperment somewhere in the middle because the genes mesh and it’s a 50-50 split to produce something somewhere in the middle? OR - do you think the foal will either get the back you hope for from the shorter backed sire or easier temperment of the sire? I guess I’m trying to ask is it possible for the traits to be a combination or actually just expressed independently and the foal is a combination by way of each trait coming through as it is from either the sire or dam. And then the true combination comes through in the next generation? This is too scientific for me, but just wondering what the answer is or what you think. TIA
PennyG
Some types of traits are dominant and express in the offspring, while others do not. Generally speaking you do not want to chose the opposite of a trait to get “in the middle”. For example, if you have a mare that is strait behind you would not want to chose a stallion that is sickle hocked. You would want to to pick a stallion with correct limbs. Or if your mare toed out you do not pick a stallion that toes in. You pick a stallion that has correct front limbs (and even more ideally passes on that trait with some consistency).
Other genes appear to “mesh”. For example, if you breed a 16h mare to a 12h stallion you will get offspring in the “middle height range”. But these are usually not traits that you are trying to “correct”
[QUOTE=TKR;7672518]
Just pondering how this works and thought I would ask your thoughts. Do you think when you breed a stallion to a mare, the genes are processed so that they are combined to reach a median or the resulting foals combines the genes independently and their traits are not actually a combination of the genes meshed together but each separately expressed in the foal’s makeup. If you are trying to shorten a back or tone done a sensitive/hot mare – are you thinking the foal will get a back or temperment somewhere in the middle because the genes mesh and it’s a 50-50 split to produce something somewhere in the middle? OR - do you think the foal will either get the back you hope for from the shorter backed sire or easier temperment of the sire? I guess I’m trying to ask is it possible for the traits to be a combination or actually just expressed independently and the foal is a combination by way of each trait coming through as it is from either the sire or dam. And then the true combination comes through in the next generation? This is too scientific for me, but just wondering what the answer is or what you think. TIA
PennyG[/QUOTE]
Traits are determined by the gene or genes responsible for those traits. The foal has two copies of each trait (most all) and as to which one is exhibited depends on how that trait is expressed, dominate, recessive, co-dominate, several genes for one trait or one gene many traits (Epistasis and pleiotropy).
But the important thing to remember is that the parent also has two copies and (mostly) randomly sorts one copy of either version into the egg or sperm. So the resulting foal is a random combination of both parents and then the laws of how those genes are expressed.
Breeding is a crap shoot in that you are not going to have the same results from a mare/stallion combination as every foal will be different and carry different combinations of the parents.
Breeding also depends on starting with the best parents possible so that the resulting combinations give you the best chance at a successful outcome.
For simple traits, like height, sometimes you get a split, sometimes more of one parent than the other.
But many traits are the result of an interplay of genes and are very hard to predict - I’d put personality under that category.
I’ve got a full brother and sister that are registered Oldenburg and are half Arabian. The older one, the gelding looks like a clone of his sire, Budweiser. His sister looks like her dam, but a bunch bigger and with a few minor differences (since I had wanted a baby that was just like my mare, but bigger, I was very happy with her). They are both chestnuts with four high white socks and white markings on their faces.
OTOH, I had two fillies out of the same mare by Landkoenig. They look like twins.
Thanks! Stoicfish, that was actually the kind of information I was seeking and the video was really cute and informative, too! I have been breeding for over 30 years, so I get the “crap shoot” and the obvious as far as not going for over correction of a trait and breeding the best possible individuals and pedigrees. I was just more interested in how the genes were expressed and if they could actually combine or not. Thanks again!
PennyG
There are simple dominant/recessive genes and then there are traits that multiple genes contribute to as well as an environmental influence on some. So that’s where quantitative genetics comes in. You start to talk about heritability factors instead of dominant /recessive. For instance, longevity is considered highly heritable so if the parents lived to a ripe old age, the offspring is likely to also.
So if a trait is qualitative - i.e., male or female; chestnut or bay: often one gene from either mom or dad is considered dominant. It gets expressed at the expense of the normal gene. So, for example, horses that are CC or Cc will not be chestnut, because the C allele changes the way that pigment migrates through the hairs. One ‘C’ allele is enough to overcome a ‘c’ (recessive) allele. Only a cc horse can be chestnut, and only the gene at that locus affects chestnut coat color.
There are some instances where a horse will show “blending” of its parents traits. For example, if you breed a homozygous HYPP stallion to a normal mare. H/H x N/N = H/N. The stallion will most likely have a severe case of the disease, the mare obviously will have no symptoms. The offspring will show varying levels of penetrance- that is, it will not be as severely affected as a homozygous individual, but it will likely show some symptoms. But again, only the HYPP gene affects HYPP status.
For traits that are quantitative, it gets complicated. These are genes like mature height, weight, quality of gaits etc. Imagine these are the traits that if you took samples from the entire population, you would get a bell curve. These traits are influenced by lots of genes, as well as things like environment, nutrition, stress etc. Usually both copies of these genes get expressed, and contribute (although not necessarily equally) to the physical trait.
For example, high birthweight is correlated to better chance of neonatal survival (evolutionarily speaking, good for dad = more genes passed on), but higher rates of dystocia and other problems for mom. There is a gene, IGF2, that when highly expressed in the developing fetus, contributes to weight gain. The maternal allele of IGF2 is modified as such so that it can’t be easily accessed = low levels of IGF2. The paternal allele is modified so that it can be accessed = high levels of IGF2.
There’s also a statistical phenomenon called “regression to the mean.” For example, the offspring of very tall parents will be tall, but not as different from the average height than their parents were.
As far as the next generation goes, genes are randomly assorted.
So if a sperm (ABcD) meets an egg (abCd) to make baby colt= AaBbcCDd
Baby colt can have sperm that are ABCD or abcd or AbcD or… you get the idea
The best way I ever heard genetics explained was this: Think of each parent’s genes as a deck of cards. With each mating, each parents genes get “shuffled” and the needed number of cards from each parent go to make up the “baby”. So the shuffling results in each offspring potentially getting completely different genes, for the most part.
They get shuffled, but I’ve read that it’s more complicated than that, in the sense that segments of DNA go together, so you might get a bunch of genes that are located near one another go as a piece.
[QUOTE=SportArab;7673863]
They get shuffled, but I’ve read that it’s more complicated than that, in the sense that segments of DNA go together, so you might get a bunch of genes that are located near one another go as a piece.[/QUOTE]
Yes the chromosomes where the genes are located are what split and it is the chromosome of each parent that is inherited. Think of a chromosome as a box of goodies but you don’t get to pick the goodies out you have to take all of them .
EXCEPT then the chromosomes can recombine where one end of the chromosome splits off and leaves part of the old chromosome behind and swaps for a new end. That also happens on a predictable basis
As noted depends on the trait, but in general terms you get something from the sire / dam and not a blend of the 2. And sometimes it throws back to grandparents, not just parents. I have 2 sisters that are Wb/tb cross. One favors her wb sire, the other favors her TB dam. With the 2 full brothers ( sons of the TB looking WB mare above) again: one looks TB in type, one throws back to his WB grand sire .
I would also say that you very often see traits from the grandparents crop up, so it’s best to know what’s in your pedigree, at least that far back.
[QUOTE=SportArab;7675222]
Breeding also depends on starting with the best parents possible so that the resulting combinations give you the best chance at a successful outcome.[/QUOTE]
This absolutely. Summarizing genetics is really difficult. I took an entire course in college and again in medical school on genetics, and I STILL do not fully understand the complexities. Genes can have variable penetrance meaning some offspring who get the gene will show the full effect, and others only a partial effect. Random mutations can occur. Genes are expressed in various ways and at various times in our life.
Some of the current research I find MOST interesting is the growing field of epigenetics which looks at how events (like feast or famine) during development of sperm in male adolescence or during a woman’s pregnancy can cause small changes in the DNA (usually addition of methyl groups) that cause changes in expression of the modified gene which go on to affect several generations of offspring. Famine has been shown to effect whether one’s children and grandchildren are obese or thin, to effect their longevity, and to effect whether or not they develop mental illnesses like schizophrenia. So, whether or not a stallion is really fat or really thin in adolescence could, theoretically, affect the metabolism of his offspring for several generations. How a mare was treated when she was pregnant could affect the personality of her offspring, possibly for more than one generation.
Some good pretty readable articles if you are interested:
http://www.news.leiden.edu/news/dutch-hunger-winter.html
http://blogs.psychcentral.com/no-family-madder/2013/11/thanks-but-no-thanks-for-the-famine-that-drove-us-crazy/
http://discovermagazine.com/2013/may/13-grandmas-experiences-leave-epigenetic-mark-on-your-genes
http://www.nytimes.com/2012/09/09/opinion/sunday/why-fathers-really-matter.html?pagewanted=all&_r=0
Thought provoking!
When people ask me how tall their children will be, I tell them to look at their family. If you are 6’9" and married to Michael Jordan, your kids will likely be tall. If you are 5’2" and married to Danny Devito, your kids will likely be short. But, every once in awhile, you see a tall family with one short kid or visa versa. The famous National Geographic photo of the beautiful woman from Afghanistan with blue eyes shows how those recessive traits can pop up generations later: http://ngm.nationalgeographic.com/2002/04/afghan-girl/index-text
If you are breeding a 15.2 hand mare and want a taller foal, breeding to a taller horse is a good plan, but not by far a foolproof one. If you REALLY want a tall horse, breed a 17.2 hand mare to a 17.2 hand stallion and you are much more likely to get what you want.
Hope that was slightly helpful… :winkgrin:
