What Can Possibly Go Wrong? Nondisjunction!
Nondisjunction is when the chromosomes fail to separate properly during Meiosis. This failure can happen either due to chromosomes failing to separate during Anaphase I or sister chromatids failing to separate during Anaphase II.
As a result of nondisjunction, a gamete to have either an extra or a missing chromosome, which can result in a plethora of issues.
As a result of nondisjunction, a gamete to have either an extra or a missing chromosome, which can result in a plethora of issues.
Example: Trisomy 21
Trisomy 21 refers to an individual that has three copies of chromosome 21. This oddity results in Down Syndrome.
One parental gamete has two copies of chromosome 21 as a result of disjunction. The other gamete is normal and thus has only one copy of chromosome 21. When the two gametes fuse together, the organism has three copies of chromosome 21.
One parental gamete has two copies of chromosome 21 as a result of disjunction. The other gamete is normal and thus has only one copy of chromosome 21. When the two gametes fuse together, the organism has three copies of chromosome 21.
Karyotyping
We can spot such oddities by karyotyping, which is a visual of all the chromosomes in a cell. The chromosomes are arranged according to size. A karyotype is an image of the chromosomes in their homologous pairs, arranged from largest to smallest, ending with the sex chromosomes.
The karyotype below is for a female with Trisomy 21 (see above)
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The karyotype below is for a female with Trisomy 21 (see above)
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A karyotype can be made from human cells, normally white blood cells of adults or from the fetus. It can be used to determine the gender of the baby before it's born and is also used to see if there are any chromosomal disorders caused by non-disjunction.