Message-Id: <199904292014.PAA09829@subcellar.mwci.net>
From: "eric nielsen" <entfolks@mwci.net>
To: "Pinhole Listserv" <pinhole@exploratorium.edu>
Subject: guys, gals, and probability
Date: Thu, 29 Apr 1999 15:04:54 -0500
ok, try this on for size --
Assume for the moment that the girl is the elder sib. Let us turn back the
hands of time to some convenient moment -- how about the moment immediately
before her future brother's conception?? This girl has a 50% chance of
getting a brother & a 50% chance of getting a sister (differential sperm
swimming rates & gender-driving genotypes aside) .
Linking this back to the diagram at
http://scienceguy.webjump.com/mendel1.jpg , it doesn't matter whether the
female is Individual "A" or Individual "B" -- could be either. The "A" &
"B" is just an arbitrary designation. When you make the observation that,
e.g. "A" = female, YOU ELIMINATE **THE ENTIRE COLUMN** under the
contingency "A"=male. You do not get to retain EITHER CELL in the column
which represents the contingecy "A"=male.
If you're not cozy with A&B as arbirary deignations, the let "A" be the 1st
sib & let "B" be the 2nd sib.
if the female is the 1st sib, column "A"=male disappears *COMPLETELY* & she
has a 50/50 chance of having a brother or sister.
if the 2nd sib is female, the row indicating "B"=male disappears
*COMPLETELY* and she has a 50/50 chance of having a brother or sister.
figure it also this way. the gender determination of a person's bro/sis is
no different from the gender determination of anybody else. your brother,
you sister -- doesn't matter -- each of us individually had that 50/50
chance. Just because a person is a sib does not make the gender
determination process any different from pulling an individual at random
out of the population at large (save for the quirk possibility of
gender-driving genotypes as per above).
how'm I doin'????
Eric
http://scienceguy.webjump.com
