The following article has a good explanation of this subject. https://www.psychologytoday.com/articles/201109/the-incredible-expanding-adventures-the-x-chromosome The X-chromosome is passed down as a recombination of the mother’s 2 x chromosomes as Robert said. Because the inactivation occurs at the embryo stage, this results in whole regions having one of the X’s active, while other regions have the other X active. This does have consequences for X-linked conditions such as red-green color blindness. If a female inherits one gene for color blindness, she is not as completely affected as a male with his one and only X, but special color blindness tests can show that the woman is affected. Vernon Smith ---------------------------------------------------------------------- Message: 1 Date: Thu, 9 Nov 2017 14:06:57 -0800 From: Robert Paine <[email protected]> To: <[email protected]> Subject: Re: [DNA] x Chromosome Question Message-ID: <[email protected]> Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Marleen Usually the X-chromosome is passed down as a recombination of the mother's 2 X-chromosomes but an X can be passed down intact in about 20 to 25 % of the births. X-inactivation or lyonization is still poorly understood but it was not my impression that the X was deactivated as an entire chromosome but as section of one or the other copies of the chromosome. X-based diseases would be affected by how the deactivation works. (Issues like hemophilia or color blindness) RPaine -----Original Message----- From: Marleen Van Horne Sent: Thursday, November 9, 2017 1:37 PM To: [email protected] Subject: [DNA] x Chromosome Question A woman gets one x chromosome from her father and one from her mother. "Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in cells other than egg cells. This phenomenon is called X-inactivation or lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells." When a woman conceives, is the x chromosome she passes to the child a complete copy of one or the other of the x chromosomes she inherited from her parents, or is it a mix and match version of her two x chromosomes? It might seem late in the game for me to be asking this question, but I have always found it confusing. Marleen Van Horne -------------------------------