Faid
Posts: 1143
Joined: Mar. 2006
|
Well, since we're now discussing loss of functions again, can you answer my question, dave? This is the fifth time I'm asking...
Oh, about the Down Syndrome thing: I'm not sure what you're trying to say. Are you saying that a fusion is responsible for its occurence? That's simply not true. For the vast majority of cases, failed disjunction (sp?) is the reason: and that's affected by things like the mother's age etc. Now, a quick glance at my old textbooks told me that there are in fact a few cases of DS attributed to chromosome fusions (Robertsonian translocations); but those are like, 3% of the total number.
Or is it that you are claiming that all fusions have such disastrous effects? That is also extremely incorrect. In all the people in the world today, more than 1 in 1000 has a kind of Robertsonian translocation. Most of those are "balanced" fusions, and their carriers have no phaenotypic problem. It has been suggested that these people might have an increased risk in giving birth to children with genetic defects (like Down), but recent studies propose that the risk is much smaller than previously thought.
As for other mammals: Robertsonian translocations of various kinds are quite common, especially in horses and cows, with only a minor drop in fertility as a result -which may pose problems for selective breeding, but none for the animal's survival. IIRC, there's also a kind of antelope where a RobT is so common and without problems, the population of the species has three distinct caryotypes, with 24, 25 and 26 chromosomes.But I'll cave to check that out.
--------------
A look into DAVE HAWKINS' sense of honesty:
"The truth is that ALL mutations REDUCE information"
"...mutations can add information to a genome. And remember, I have never said that this is not possible."
|
