Incomplete Dominance

Strutter769 · 05-06-12, 06:36 PM

No, I'm not writing about my private life. It's about genetics, people!

Will someone please try to help me better understand this? O understand about a red flower and white flower making all purple flowers, but I don't understand "exaggerated form" or how heterozygous animals can carry the visual trait.

Teachers, my hand is raised! :-D

rullom · 05-06-12, 06:57 PM

well with regards to incomplete dominance I will assume you have zero genetics background and try to keep this simple.....In simple terms you get a combination of the two "modes" of the trait when they are expressed in combination (one form mother one from father)....Like eye colour might be a shade mix between the two parents due to the colour expressed by maternal and paternal genes that the individual would inherit.

With regards to heterozygousity; What you need to know first is that for a particular gene you can have two physical characteristics lets say. So lets say for vision it is based on the genes inherited from both mother and father .... 1 from each to make a combination of the maternal and paternal genes. Lets call it "blank blank" _ _ since we don't know yet what we are getting. Now the possible combinations for vision lets say (and I am making this totally up is the following:
VV = Normal vision when this combination of genes are expressed
Vv = Normal vision ....
vv = Blind .... when this combo is expressed
One could be considered a (physical) dominant characteristic and the second could be whats referred to a recessive characteristic(physical). Now what determines which is dominant and which is recessive is arbitrary but the term dominant means that you only need to inherit one (i.e. capital VV to receive the dominant trait which is "normal" vision)
Recessive would be vv = blind vision . So dominance means you only need one to determine your physical characteristic. The other is over rides in a sense. Recessive you need both to express the physical characteristic.
Now with respect to "carrier status" in order to be a carrier you must (1) not express the gene yourself and (2) be able to pass it on.... Heterozygous means you are "HETERO = different = you have one V and one v ==> your combination is "Vv". HOMOzygous means the same so you would be VV or vv depending on what you are homozygous for.
Now this would happen in only one way given the combos I stated above:
If you are Vv you would have normal vision but you can pass on to your children either the "V" or "v" since that is "your" genetic make up for vision... so when you have kids you pass to each child EITHER V or v. This is a random event and I am giving you a very simple case. i hope I didn't botch up my terminology trying to keep this simple but you get the idea. Let me run you by what is called a monohybrid cross which is the simplest scenario:
Father has normal vision and is VV
Mother has normal vision and is a carrier Vv
To determine the possibilities on what your kids would have you do this:...make a table 2x2:
Father
V V
-------------
Mother V / VV / VV /
v / Vv / Vv /
--------------
Now the inside cells are VV VV Vv Vv depending on the combination of father and mother genes passed on... the way you get each cell is just combine the first from the father = V with the first form the mother = V ... this yields the first cell VV. Do the same for the rest of the cells but change which one you use form the father and mother.
So our results indicate that there is a 50% chance that our children will be carriers...Vv and 100% that all children would be normal vision.
So you might guess the only way to get abnormal offspring is if you have carrier mother and father so you are able to get vv as a combination. Do the cross and you will see 25% or 1/4 chance of getting abnormal offspring.
Hope I didn't make a mess of this. I doubt very many people have some genetics background on here but hope this helps. My experience is up to 3rd year university for genetics .... if you need more but simple it gets hard to explain but I can try.

rullom · 05-06-12, 06:59 PM

Sorry I just noticed that my 2x2 table messed up .... draw it like this.
Make one heading "father" and underneath write "V V". Then make a second row and label it mother. going sideways write V v (like a grid ... top columns are labeled V V and rows are labeled V v) The results of the cells you can see above are separated by / /. The 4 cells should be when you are done VV VV Vv Vv

Strutter769 · 05-07-12, 09:59 AM

Rollum, thanks for the write-up! I think this might be the case with the Sunburst Mad Boas I'm trying to research now, judging by the appearance of the two original parents' appearance.

But, if I'm not mistaken, this is different than most BRB litters in that most will color like one of the parents, but some do look like a combination of both; those being the animals showing incomplete dominance.

Is my understanding correct?

Gregg M · 05-08-12, 09:24 PM

You still can not come to a conclution. It also sounds as if it can be a polygenic trait. Or as some like to call it, "line bred".

Strutter769 · 05-08-12, 09:29 PM

And that can't be proven until the offspring are old enough to mate, is that also correct?

I will be outcrossing the Sunburst that I obtain this summer, so it'll be about 10 years before I create any Sunburst myself.... by my calculations.

rullom · 05-09-12, 03:59 PM

Sorry I thought you knew the genes that the parents had.....you are working backwards form offspring to figure out what the parents have?? That is incredibly hard. you need some statistical methods....basic ones I have done in the past. You also need a larger sample than just one unless it is really basic. And as the above mentioned if it is multifactorial etc you will never figure it out