Women who carry the defective gene can pass an abnormal X on to their sons. Since boys have an X from their mother and a Y from father, there is no second X to make up for the defective gene from the carrier mother.
affected males 2/3 of the time inherited the mutation from the mother while 1/3 of the time the mutation is de novo, or new.
A common abnormality is caused by nondisjunction, the failure of replicated chromosomes to segregate during Anaphase II. A gamete lacking a chromosome cannot produce a viable embryo. Occasionally a gamete with n+1 chromosomes can produce a viable embryo.
Citation(text):
1)http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookhumgen.html
2)CDC’s National Center on Birth Defects and Developmental Disabilities (previously listed below as "Duchenne/Becker Muscular Dystrophy, NCBDDD, CDC")
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