twins but only has a allergy

[mollykins]

Factor, I wonder if you can even the score which stands one nil to nature vs science teachers. My biology teacher didn't have a clue what the answer was.

There were two (obviously) identical twins in my science class, but only one of them has an allergy to; baked beans, cats and dogs (probably fur in general). But the other doesn't, and neither does anyone else in their family.

If it was genetic, which they both share, they'd both have it. if it was in their environment, which they both share, they'd both have it. But only one does.

so factor, and anyone else who has an answer, how and why has this happened in identical twins who share identical genes and an identical environment (they've never spent a day apart).

[daffy654]

Allergy is a 'learned' response. You have to have been exposed to an allergen for the reaction to develop. My daughter's allergist told me that it is impossible to develop a true allergic reaction to a substance the very first time you encounter it.
As far as I am aware, being allergic to something is not down to genetics, so twins (identical or not) have no greater chance of developing one than any other two non-related people.

[bobjugs12]

Different dads?









;-)

[mollykins]

They're identical (well very nearly, it took me over a year to be able to tell them apart)

[RATTER15]

Im totally with daffy on this one.

[Sqad]

Identical twins are not necessarily identical, they may share the same ovum (egg) and placenta, but not necessarily the same mitochondria which predicts likes and dislikes etc.

Genetics play a part in Allergy, but the environment plays the greater role and although they have both been exposed to the same antigen in the environment, their bodies (antibodies) have been "triggered"at different times.
It is likely that that the unaffected twin will also develop the same allergy but later in life.

[mollykins]

aaahhhhhh, is it bad that someone with a masters in some kind of biology didn't know that?

[redcrx]

if you can tell them apart then they cant be identical, can they

[ummmm]

Red...you can tell them apart once you know them...

[mollykins]

The only difference was in their voice and one had to have a retainer. Plus one tended to have her hair up more than the other.

lessons were fun with them.

[mollykins]

I think, the one with the retainer had her hair up more and had a slightly deeper voice.

[redcrx]

its as sqad was saying, they are not identical in every way, if one has a different voice then why cant they have different allergies?

[mollykins]

because the accent has developed slightly different perhaps.

[redcrx]

so allergies could also develop differently.

[4getmenot]

environment cant come into it otherwise growing up i'd have same allergies as redcrx

[ummmm]

Explain this....twins...one placenta...non identical.

One of them actually looks more like my daughter than her sister (cousins)

[jomifl]

nothing is identical to anything else, it can't be because it is not in the same place so it is responding to a (slightly perhaps ) different environment. That includes twins.

[Huderon]

Perhaps it's similar to a cloned animal (a cat if I remember correctly) having a different pattern of fur colour to the original. The genes may be identical, and the environment, but it's the way the genes are expressed which matters. I'll let someone else explain what is ment by the way the genes are expressed though :-)

[mollykins]

Some are turned on and some are turned off, but if they were genetically identical I don't see why they don't appear so.

[theprof]

Sqad is absolutely correct. Whilst monozygotic (identical) twins do have the same genes, their mitochondria are not identical as they contain different mitochondrial DNA. In practical terms, this means that each twin can react differently to everything from cigarette smoke in the environment to foodstuffs. In addition, they can also respond differently to infections and medications.

Research by Bruder and Dumanski at the University of Alabama has also shown that something called copy number variation (CNV) is also responsible for response differences in monozygotic twins. CNV refers to differences in the number of copies of an individual DNA segment between two or more genomes ( A genome is the full complement of genes carried by a single set of chromosomes). CNV can occur when pieces of DNA are missing from the chromosomes of the parent, causing the offspring to have only one copy of that piece of DNA. Furthermore, mutations can produce many copies of a particular “bad” bit of DNA. What this means is that twins are not 100% identical as their DNA can be minutely different due to CNV. Prior to this research it was often thought that the environment was the reason why one monozygotic twin would develop a disease such as Crohn’s disease or have a differing susceptibility to AIDS over another monozygotic twin. Incidentally, there is even a specialist name for identical twins that display such variations: they are called discordant monozygotic twins

As far as your teacher’s concerned mollykins, this sort of stuff is not particularly advanced and is taught during routine genetic tutorials to students taking basic BSc biology degrees at universities throughout the world. The only thing I can add is that I’m absolutely certain he’s not a life sciences graduate of any of the colleges at my university!

Never mind - just ask him next time you see him to explain discordant monozygotic twins to you!