>I think in your example A and B would be different genes not just different locations on some chromosome for the same gene in different species.

Correct, A and B are different genes. One codes for one thing (perhaps tyrosinase), and the other codes for something else. If both function properly, the snake looks normal. If the A gene pair is not functioning, the snake does not have black pigment. If the B gene pair is not functioning, then there is no black pigment. If neither the A pair nor the B pair is functioning, there is no black pigment.

Tyrosinase does not make melanin all by itself. Tyrosinase catalyses two of the chemical reactions in the synthesis of melanin. There are a number of other chemical reactions before melanin is formed. Then the melanin is laid down in a protein matrix to form the pigment granule. Maybe A codes for tyrosinase production and B codes for one of the steps in the production of the protein matrix. I don't know. But I do know that the making of normal coloration requires a lot more than one gene pair.

Paul Hollander

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• Alb nelsons and alb ruthvens question - Jeff Schofield, Sat Feb 9 16:39:48 2008
• RE: Alb nelsons and alb ruthvens questio - charleshanklin, Sat Feb 9 16:53:48 2008
• See, thats what is really helpful,thanks - Jeff Schofield, Sat Feb 9 18:40:20 2008
• RE: See, thats what is really helpful,th - vjl4, Sat Feb 9 19:22:38 2008
• RE: See, thats what is really helpful,th - Jeff Schofield, Sat Feb 9 20:43:03 2008
• RE: See, thats what is really helpful,th - rtdunham, Sun Feb 10 10:59:43 2008
• RE: See, thats what is really helpful,th - vjl4, Sun Feb 10 13:22:19 2008
• RE: See, thats what is really helpful,th - Tony D, Mon Feb 11 09:25:28 2008
• RE: See, thats what is really helpful,th - vjl4, Mon Feb 11 10:51:53 2008
• RE: See, thats what is really helpful,th - Tony D, Mon Feb 11 12:28:05 2008
• RE: See, thats what is really helpful,th - Paul Hollander, Mon Feb 11 17:32:55 2008
• RE: See, thats what is really helpful,th - charleshanklin, Sat Feb 9 19:34:57 2008