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Examples of Karyotypes with 46 Chromosomes and with Trisomy 21
Mitosis - How Most Cells Are Made
Meiosis - How Most Sperm and Egg Cells Are Made.
(a) Usually a cell with 23 pairs of chromosomes divides, making gametes (either egg or
sperm) with only 23 chromosomes. (b) Sometimes, a pair of chromosomes does not
separate, and both chromosomes of the pair (for example, two chromosomes 21) go into the
same egg or sperm with 24 chromosomes (an extra one) and another with 22 (missing one). |
| One Way Mosaicism Occurs - Nondisjunction After Conception.
Only the chromosomes 21 have been shown in this diagram. However, the cells
contain either 46 chromosomes (with two 21's; shown as open circle) or 47 chromosomes
(with three 21's; shown as filled circle). |
| A Second Way Mosaicism Occurs - Nondisjunction Before and After
Conception. Only the chromosomes 21 have been shown in this diagram.
However, the cells contain either 46 or 47 chromosomes (with two 21's; shown as open
circle) or 47 chromosomes (three 21's; shown as filled circle). |
Milestone Attainment of Individuals with Mosaic DS and
Their Siblings, As Reported By Their Parents
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