Genetics question

Mr V Mulholland lsrdp at
Wed Aug 24 09:25:39 EST 1994

Clay Luther (monsta at wrote:
: Unsure if this is the correct place, but it seemed the most appropriate...
: I have a layman's question for the knowledgeable.

: Here's a family tree:

:  Great Grandad (X'Y) - Great Grandma (X?X?)
:                      |
:                   Grandma (X'X?) - Grandad (X^Y)
:                                  |
:                                 Mom (X'X^) - Dad (X?Y)
:                                            |
:                                          me (X'Y)

: Great Grandad is color blind. Grandad is bald. From what I remember from
: high school genetics, both of these traits are sex-linked, carried on
: defective X chromosomes.

: So, in the above picture, X' represents the X chromosome carrying the color 
: blindness gene, and X^ represents the X chromosome carrying the baldness 
: gene. X? represents an X chromosome that I don't know about.

: I am color blind, and my brother is not. Does this mean my brother should
: start saving up for Rogaine? 

: Or do the genes get transmitted independently from the chromosomes they 
: reside on (in some great genetic shuffle)?

: It's been 10 years since high school genetics. It's taken me 10 years
: to consider this possibility, so be gentle.

: Email responses greatly appreciated.

: --
: cpearce at

Dear Clay,

I'm not sure that baldness is sex-linked. However, I'm pretty sure that it is
sex-limited. This means that both males and females can carry the genes which
would produce baldness, BUT the baldness phenotype (and I'm just referring to
male pattern baldness, not other sorts) is only expressed in males. This 
would make your family tree incorrect.

Vince Mulholland

			  (o o)
 * Vincent Mulholland	    		E-Mail: lsrdp at	*
 * Department of Biological Sciences	Phone : 0203 523523 Ext. 2572	*
 * University of Warwick,		Fax   : 0203 523701		*
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