Extra copies of the other chromosomes are probably fatal to the developing embryo that's why individuals with extra chromosome 21 are more numerous than extra chromosomes 3 or 16.
The term "aneuploidy" in genetics refers to the alteration in chromosomal number 23, which can result in hereditary disorders. An individual is said to be aneuploid if they have fewer chromosomes than the wild or euploid type due to an additional or missing chromosome, which is invariably linked to a lack of either physical or mental development or both. This happens during errors in meiosis, the type of cell division that takes place during the development of gametes, which are sex cells that give rise to zygotes during fertilization.
Non-disjunction is a failure of the meiotic process, in which two chromatids or chromosomes pair up and one pole receives nothing. When homologous chromosomes fail to split properly during meiosis I, two defective cells are produced as a result: one has an extra chromosome and the other lacks a chromosome. The chromatids in the chromosomes separate during meiosis II, which may also result in the formation of abnormal cells.
The trisomy on chromosome 21 is more prevalent because the condition is not fatal. Trisomy on a different pair of chromosomes, however, can often be fatal. Having an extra chromosome impacts the way a newborn develops both physically and intellectually. The newborn and future adult may face a variety of mental and physical difficulties as a result of these changes. This is because the DNA in those chromosomes changes how much protein is made and is encoded by them.
The complete question is:
Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?
(A). There are probably more genes on chromosome 21 than on the others.
(B). Chromosome 21 is a sex chromosome, and 3 and 16 are not.
(C). Down syndrome is not more common, just more serious.
(D). Extra copies of the other chromosomes are probably fatal to the developing embryo.
(E). The nondisjunction of chromosomes 3 and 16 probably occurs much less frequently.
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