Mosaicism
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General Information
Typical chromosome patterns are either 46XY or 46XX. Someone with "mosaic" chromosomes has different chromosome patterns in some cells of their body than in others. This results from random differences in how the cells divide while the embryo is growing. Due to how this process occurs, someone with mosaicism will usually have different numbers of chromosomes in different cells, such as 45X/46XY or 45X/46XX (both of which are variants of turner syndrome) or 46XX/47XXY or 46XY/47XXY (which are both variants of Klinefelter Syndrome).
Someone with specifically 46XX chromosomes in some cells and 46XY in others most likely has the intersex variation of chimerism instead of mosaicism.
Mosaic chromosomes can cause someone to develop variations in their gonads, genitals, or hormone function. As an example, if someone has at least one Y chromosome, they may have both testicular and ovarian tissue, or genital differences such as hypospadias. They may also develop some secondary sex characteristics at puberty that are not expected for the sex that they were assigned.
Someone without a Y chromosome and mosaicism (e.g., 45X/46XX, or 46XX/47XXX) may have "streak" gonads or may have ovaries that stop functioning at an earlier age than typical, which can cause someone not to experience the changes associated with a typical estrogen-based puberty. It can result in infertility later in life.
Some people with mosaicism may not have any noticable signs that they have it.
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