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Down syndrome (trisomy 21) occurs when a gamete carrying an extra copy of chromosome 21 is involved in a fertilization event.
The gamete (whether sperm or oocyte) has an extra copy of chromosome 21 because of something called NONDISJUNCTION. This happens when a chromosome gets pulled to the wrong daughter cell.
This can happen either in meiosis I or meiosis II.
If nondisjunction happens in meiosis I, 2 gametes will be n+1 (have the extra copy of 21) and the other 2 gametes will be n-1 (will have NO copy of 21)
If nondisjunction happens in meiosis II, 2 gametes will be normal, one will be n+1 and one will be n-1.
What else can I help you with?
In which stage of cell division, mitosis or meiosis, does crossing over occur?
Crossing over occurs during the prophase I stage of meiosis.
In what stage of the cell cycle does division occur?
the answer should be gamete and if not its either mitosis or meiosis
Where does interphase occur?
Interphase occurs in the cell cycle, between cell divisions. It is the stage in which the cell grows, carries out its normal functions, and prepares for cell division.
In what part of the cell cycle does replication occur?
DNA replication occurs during Interphase. This is not normally part of the cell division cycle but interphase must occur before subsequent stages such as prophase and metaphase can occur.
What does not occur during interphase excretion of wastes cell repair protein synthesis nuclear division?
Nuclear division does not occur during interphase. Interphase is a stage in the cell cycle where the cell grows, carries out its normal functions, and replicates its DNA in preparation for cell division. Nuclear division occurs during other stages of the cell cycle, such as mitosis or meiosis.
Which stage of cell division show the division of nucleus?
tatanga tngahan
Which stage of labor does crowning occur?
expulsion stage
What stage does the deepest sleep occur?
stage 4
Does genetic engineering benefit Down syndrome?
No. Gene therapy alters a person's genetic code, generally by inserting a genetic sequence. Trisomy 21 (downs syndrome) is caused by the presence of a copy (or part of a copy) of the 21st chromosome. Genetic therapy would not be able to remove this extra chromosome. It might be possible (in the future) to "turn off" the extra chromosome, and stop trisomy-21 at the embryo stage. However, by the time a person is born, the physical damage from downs syndrome has been done. After a few months to a year or so, the mental damage from downs syndrome will also be done. So no "treatment" for downs syndrome will be possible using genetic modification such as gene therapy.
What stage of the general adaptation syndrome does a rat enter when it is first introduced to an overcrowded cage?
alarm stage
What is the 1st stage of cell division?
interphaseprophaseanaphasetelophasecytokinesis
What phase does preparation for cell division occur?
during interphase the cells prepare for the divsion and the DNA replicates and chromosomes form
