Down's syndrome is caused because of the extra 21st chromosome.From where does this chromosome comes?

Answer 1

One of the chromosomes fails to separate into daughter chromosomes during meiosis. This is called nondisjunction. As a result, you get one normal chromosome from one parent, and then, from the other parent, you get the unseperated chromosome, which eventually separates later. The end result of this is 3 chromosomes. As the person above me said, it is usually the mother's gamete that delivers the "nondisjunctioned" chromosome.

Answer 2

you have that right. Down Syndrome is caused because of an extra 21 chromosome, also known as trisomy 21. The 21st chromosome is an autosomal chromosome ie it doesnt determine the sex of the organism but does other stuff. Also u get one 21 from each parent, but sometimes due to some problems with cell division the the cell ends with 3 21 chromosomes instead of the regular 2.

Answer 3

In Down's syndrome the extra chromosome 21 comes from nondisjunction gamete (i.e., a sperm or egg cell) from either the mother or the father. 88% comes from nondisjunction in the maternal gamete and 8% comes from nondisjunction in the paternal gamete.

The extra chromosomal material can come about in several distinct ways. A normal human karyotype is designated as 46,XX or 46,XY, indicating 46 chromosomes with an XX arrangement for females and 46 chromosomes with an XY arrangement for males.

Trisomy 21 (47,XX,+21) is caused by a meiotic nondisjunction event. With nondisjunction, a gamete (i.e., a sperm or egg cell) is produced with an extra copy of chromosome 21; the gamete thus has 24 chromosomes. When combined with a normal gamete from the other parent, the embryo now has 47 chromosomes, with three copies of chromosome 21. Trisomy 21 is the cause of approximately 95% of observed Down syndromes.♥

Answer 4

a) is strictly backwards: The chromosomes are numbered via length: so 21 is between the smallest, and hence has fewer genes than maximum different chromosomes (it incredibly is probable why this is far greater survivable than different trisomies) b) is incorrect, Chr 21 isn't a intercourse chromosome. c) isn't precise: there are greater surviving those with Down's than with different autosomal trisomies, greater often than not because of the fact Down's is way less severe, not greater severe, than different trisomies. d) is, as you have have been given guessed, the nicely suited answer e) there is not any evidence or reason to think of that it extremely is the case.

Answer 5

usually from the mother.
normally, the mother and father would give only one chromosome each, however as the mother's age increases the number of defects in her eggs also increase. if one of her eggs accidentally has 2 chromosome 21s, the child will have 3.
however I think in some cases the extra chromosome can come from the father. there doesn't seem to be a correlation between the father's age and his chance of having a downs syndrome child.

Answer 6

I think it comes from the extra duplication or the extra formation when the baby is being formed in the tummy!