gasp@bu-cs.BU.EDU (Isaac Kohane) (11/07/86)
Well, it seems that women can in fact see more than men. In Nature Vol 232 p 578: We (humankind... I'm treading on thin ice, have to watch out for net.women) are basically trichromatic. That is we have three pigments in our retina (red green and blue) each with its own characteristic peak absorption/stimulus range. Now, it appears that the long wave (red-sensitive) pigment in our cones (in our retina) is genetically coded for by a locus (jargon for "segment of") on chromosome X. Now, as we all know, women have twice as much X chromosome as men do. Therefore, if there are multiple alleles (versions of that gene at that locus) for the red pigment (as is suggested by recent experiments in this area), then a women could have one allele on one X chromosome, and another allele on the second X chromosome. Each allele would have a different peak absorption wavelength. It might be then, that some women are in fact quadrichromatic. What do they see that we don't? :-)
berleant@ut-sally.UUCP (Dan Berleant) (11/07/86)
In article <2302@bucse.bu-cs.BU.EDU> gasp@bu-cs.BU.EDU (Isaac Kohane) writes: >Well, it seems that women can in fact see more than men. >We ... are basically trichromatic. That is we have three pigments >in our retina (red green and blue). >Now, as we all know, women have twice as much X chromosome as men do. >Therefore, if there are multiple alleles (versions of that gene at >that locus) for the red pigment (as is suggested by recent experiments >in this area), then a women could have one allele on one X chromosome, >and another allele on the second X chromosome. Each allele would have >a different peak absorption wavelength. It might be then, that some >women are in fact quadrichromatic. What do they see that we don't? :-) Probably not much. Cones (the color receptor cells in the retina) project to deeper areas of the brain by 'labelled lines', that is, the nerve from the cone codes the color sensitivity of the cone. Even if a woman has two different variations of red-sensitive cone, probably sensations from both would be sent along 'red' nerves, and the net effect would be simply a wider (less frequency-specific) curve of color sensitivity to red. Dan B.
mikes@tekecs.TEK.COM (Michael Sellers) (11/07/86)
In article <2302@bucse.bu-cs.BU.EDU>, gasp@bu-cs.BU.EDU (Isaac Kohane) writes: > Well, it seems that women can in fact see more than men. > [...] > Now, as we all know, women have twice as much X chromosome as men do. > Therefore, if there are multiple alleles (versions of that gene at > that locus) for the red pigment (as is suggested by recent experiments > in this area), then a women could have one allele on one X chromosome, > and another allele on the second X chromosome. Each allele would have > a different peak absorption wavelength. It might be then, that some > women are in fact quadrichromatic. What do they see that we don't? :-) If I remember correctly, the second X chromosome in females sits unused in the nucleus (it never "unbundles" in interphase like the rest of the chromosomes do). These are called "Barr bodies", after the guy who discovered them. If my recollection is correct, then this would seem to imply that females do not benefit from anything on the "extra" X chromosome. Can anyone closer to a genetics text confirm or deny my remembrance? [It seems I have to put some extra text in here so that the news software will agree to send it. Seems my ratio of old to new text isn't quite what it should be. Welcome to net.big-brother. :-(] -- Mike Sellers UUCP: {...your spinal column here...}!tektronix!tekecs!mikes "In a quiet moment, you can just hear them brain cells a-dyin'"
wen-king@cit-vlsi.Caltech.Edu (Wen-King Su) (11/08/86)
In article <7858@tekecs.TEK.COM> mikes@tekecs.TEK.COM (Michael Sellers) writes: >In article <2302@bucse.bu-cs.BU.EDU>, gasp@bu-cs.BU.EDU (Isaac Kohane) writes: >> Well, it seems that women can in fact see more than men. >> [...] >> Now, as we all know, women have twice as much X chromosome as men do. >> Therefore, if there are multiple alleles (versions of that gene at >> that locus) for the red pigment (as is suggested by recent experiments >> in this area), then a women could have one allele on one X chromosome, >> and another allele on the second X chromosome. Each allele would have >> a different peak absorption wavelength. It might be then, that some >> women are in fact quadrichromatic. What do they see that we don't? :-) > >If I remember correctly, the second X chromosome in females sits unused in >the nucleus (it never "unbundles" in interphase like the rest of the >chromosomes do). These are called "Barr bodies", after the guy who >discovered them. If my recollection is correct, then this would seem to >imply that females do not benefit from anything on the "extra" X chromosome. >Can anyone closer to a genetics text confirm or deny my remembrance? > The red/green color blindness in human is caused by a defect in this gene. The low incidence of red/green color blindness among women is attributed to the fact that women have two alleles and that the chance of having two defective alleles at the same time is quite small. This seems to conclude that both of the X chromosomes can be expressed. However, I believe only one of them can be expressed in a cell. Certain genes for skin color and hair color can be founded on the X chromosome. If the two alleles of a skin color gene are sufficiently different and if different X chromosomes are expressed at different parts of the body, the individual would have patches of different colors over the body. I do not remember seeing this condition in human, but it is known in cats and is found only in female cats. Does anybody know of a human example? Is there anybody out there with a normal left eye and a color blinded right eye? As long as both of the X chromosomes can be expressed, whether they can both be expressed in the same cell or not, I believe if a women has two different alleles for the gene, she is going to have both type of the red pigment in her eyes.
mrh@cybvax0.UUCP (Mike Huybensz) (11/09/86)
In article <7858@tekecs.TEK.COM> mikes@tekecs.TEK.COM (Michael Sellers) writes: > If I remember correctly, the second X chromosome in females sits unused in > the nucleus (it never "unbundles" in interphase like the rest of the > chromosomes do). These are called "Barr bodies", after the guy who > discovered them. If my recollection is correct, then this would seem to > imply that females do not benefit from anything on the "extra" X chromosome. > Can anyone closer to a genetics text confirm or deny my remembrance? Yes, in each cell of a female human (sex determination methods of different organisms vary quite a bit) all but one of the X chromosomes sit around doing nothing as Barr bodies. But not necessarily the same X chromosome in each cell. If that were the case, we'd see many recessive, sex-linked traits that are carried on the X chromosome (such as color-blindness) occuring with exactly half the frequency that they do in males. So genes on both X chromosomes normally are expressed in women. -- Mike Huybensz ...decvax!genrad!mit-eddie!cybvax0!mrh
gasp@bu-cs.BU.EDU (Isaac Kohane) (11/10/86)
Isaac Kohane: >> Well, it seems that women can in fact see more than men. >> [...] >> Now, as we all know, women have twice as much X chromosome as men do. >> Therefore, if there are multiple alleles (versions of that gene at >> that locus) for the red pigment (as is suggested by recent experiments >> in this area), then a women could have one allele on one X chromosome, >> and another allele on the second X chromosome. Each allele would have >> a different peak absorption wavelength. It might be then, that some >> women are in fact quadrichromatic. What do they see that we don't? :-) Mike Sellers: > If I remember correctly, the second X chromosome in females sits unused in > the nucleus (it never "unbundles" in interphase like the rest of the > chromosomes do). These are called "Barr bodies", after the guy who > discovered them. If my recollection is correct, then this would seem to > imply that females do not benefit from anything on the "extra" X chromosome> Can anyone closer to a genetics text confirm or deny my remembrance? Close, but no cigar :-). The inactivation of the X chromosomes is a random process, such that in a given tissue, there are two populations of cells, each one having a different X chromosome activated. Therefore, both alleles would be expressed. Isaac
emigh@ecsvax.UUCP (Ted Emigh) (11/10/86)
In article <7858@tekecs.TEK.COM> mikes@tekecs.TEK.COM (Michael Sellers) writes: >In article <2302@bucse.bu-cs.BU.EDU>, gasp@bu-cs.BU.EDU (Isaac Kohane) writes: {{{{Text deleted so inews would accept this posting -- you'll have to look it up yourselves}}}} Actually, each female somatic cell has only one activated X chromosome. Which one is activated is random, and once inactivated all daughter cells will have the same X chromosome(s) inactivated. X-inactivation occurs early in development, but each eye contains a mixture of cells with each of the Xs inactivated (as demonstrated by females who are heterozygous for occular albinism). A quick search through "Mendelian Inheritance in Man" by VA McKusick does not show up any answers to this question (6th Edition, I don't have a copy of the 7th edition yet). Since we can't tell if the "Red" seen by any other person is exactly the same as the "Red" seen by use, I would think there would be no practical difference between males and females -- females may see things a little bit more red.
gagen@bgsuvax.UUCP (kathleen gagen) (11/11/86)
> In article <2302@bucse.bu-cs.BU.EDU>, gasp@bu-cs.BU.EDU (Isaac Kohane) writes: > > Well, it seems that women can in fact see more than men. > > [...] > > Now, as we all know, women have twice as much X chromosome as men do. > > Therefore, if there are multiple alleles (versions of that gene at > > that locus) for the red pigment (as is suggested by recent experiments > > in this area), then a women could have one allele on one X chromosome, > > and another allele on the second X chromosome. Each allele would have > > a different peak absorption wavelength. It might be then, that some > > women are in fact quadrichromatic. What do they see that we don't? :-) > > If I remember correctly, the second X chromosome in females sits unused in > the nucleus (it never "unbundles" in interphase like the rest of the > chromosomes do). These are called "Barr bodies", after the guy who > discovered them. If my recollection is correct, then this would seem to > imply that females do not benefit from anything on the "extra" X chromosome. > Can anyone closer to a genetics text confirm or deny my remembrance? > > -- > Mike Sellers Yes. It is correct that the second X chromosome in human females sits unused in the nucleus and can be cytologically recognized as a "Barr body". Although only one X chromosome is transcriptionally active (codes for the production of protein) in each female cell, the transcriptionally active chromosome may vary from one cell to another within the same individual. ________________________________________________________________________ Kathi Gagen
werner@aecom.UUCP (Craig Werner) (11/14/86)
In article <1229@cybvax0.UUCP>, mrh@cybvax0.UUCP (Mike Huybensz) writes: > In article <7858@tekecs.TEK.COM> mikes@tekecs.TEK.COM (Michael Sellers) writes: > > If I remember correctly, the second X chromosome in females sits unused in > > the nucleus (it never "unbundles" in interphase like the rest of the > > chromosomes do). These are called "Barr bodies", after the guy who > > discovered them. When I took cytology, the professor, Leopold Koss, in a classic line, enjoined us about the following: "These are sex chromatin bodies, not Barr bodies. Barr had a collaborator [pause], whose name unfortunately escapes me at the time." BTW, they are officially Barr-Bertram bodies, and they were first described in the neurones of female cats. Also, it is thought that at least part of the 2nd X was active. At one point, I knew the exact band. But it has to be so, otherwise Turner's and Kleinfeldter's Syndrome patients would be normal, and they are not. -- Craig Werner (MD/PhD '91) !philabs!aecom!werner (1935-14E Eastchester Rd., Bronx NY 10461, 212-931-2517) "Why is it that half the calories is twice the price?"