Thanks for bringing up this question Marleen.  I'm wondering if the answer isn't that the crossover events generally happens in meiosis rather than in mitosis.  I've always been unsure about that.  If that is indeed the case, the proviso in your quote "....other than {in} egg cells..." would explain the difference.  Can someone tell me if I now understand this aspect of crossover JAL . From: Marleen Van Horne <[email protected]> To: [email protected] Subject: [DNA] x Chromosome Question Message-ID: <[email protected]> Content-Type: text/plain; charset=utf-8; format=flowed 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.

Recombination occurs during meiosis at the 4-strand stage.  Remember that much!     John McCoy ([email protected])   In a message dated 11/9/2017 2:11:36 PM Pacific Standard Time, [email protected] writes:   Thanks for bringing up this question Marleen.  I'm wondering if the answer isn't that the crossover events generally happens in meiosis rather than in mitosis.  I've always been unsure about that.  If that is indeed the case, the proviso in your quote "....other than {in} egg cells..." would explain the difference.  Can someone tell me if I now understand this aspect of crossover JAL . From: Marleen Van Horne <[email protected]> To: [email protected] Subject: [DNA] x Chromosome Question Message-ID: <[email protected]> Content-Type: text/plain; charset=utf-8; format=flowed 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. ------------------------------- To unsubscribe from the list, please send an email to [email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message