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I once knew a girl who thought her brother was hot... [May. 16th, 2005|12:06 pm]
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From the standpoint of eugenics and biology, brothers and sisters bear a closer relationship to one another than they do to either of their parents.

[User Picture]From: vimnelius
2005-05-23 04:09 pm (UTC)

Funny, but not exactly

(warning, this turned out longer than I'd intended)

Unless you mean sisters who are bees, this isn't necessarily true.

For humans (or any other organism that has two sets of chromosomes):
Sister 1 is 50% genetically related to mom and 50% genetically related to dad, because that's where she got her chromosomes.

Sister 2 is also 50% related to mom and 50% related to dad, but not necessarily the same 50% as her sister is. If Dad gave Sister 1 a sperm cell with the exact complement of his DNA of that which he gave two sister 2 (possible but very, very unlikely), then even though Sisters 1 and 2 have the same father, they are not related from a paternal point of view. Ditto for Mom.

Likewise, Sisters 1 and 2 could have gotten the exact same complement of DNA from Dad (equally unlikely as the exact complement), at which point they are genetically identical from a paternal point of view.

Bottom line: sisters (or brothers) share anywhere from 0-100% of paternal DNA in common (50% is most likely), and anywhere from 0-100% maternal DNA in common (50% most likely). So, on average, siblings are 50% genetically similar, just like a child is 50% genetically similar to each given parent.

With bees, it gets really weird. Females have two sets of chromosomes (like humans), but males only have one (like a human sperm or egg cell). So you have two sisters. They each have 100% of Dad's DNA, since Dad only has one set of chromosomes to all of his offspring. Meanwhile, each daughter is 50% genetically similar to Mom (just like a human daughter would be). If you average 100% and 50%, you see that bee sisters are 75% genetically similar, while they're only 50% genetically similar to Mom.

What does this mean? The theory of Kin Selection suggests that this sister relatedness is why natural selection favors worker bees that don't lay their own eggs but instead help their mom (the queen) lay eggs. Each worker is biologically "better off" helping her sisters than she would be helping her daughters by laying eggs.

Strange strange strange.
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[User Picture]From: randomposting
2005-05-23 04:36 pm (UTC)

Re: Funny, but not exactly

*blinkblink* Wow! I just posted the thing from a little fact book I got from the library, but I should check it out again and give you the address to write to them and tell them they were wrong. -- That was some serious science there, and I always sucked at science, so my head's spinning a little.
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