This condition results from what geneticists call chromosomal nondisjunction, when two Although Down syndrome causes a variety of health and Trisomy 21 or Down syndrome is one of the most well-known genetic disorders. care there's no reason why people with Down syndrome can't enjoy a long, fulfilling life. Source:http://www.ehow.com/info_8626360_happens-three-chromosome-21.html
nondisjunction always results in zygote with an extra chromosome? true or false?
In meiosis, one cell will divide into 4 cells, each having HALF the number of the original cell!First there is a doubling ( as in mitosis) and then it divides twice! In these divisions the chromosome pairs all line up at the equator and then are divided equally into the daughter cells! In humans we have 23 pairs of chromosomes, or 46 in total in our somatic (body) cells and 23 chromosomes in our sperm and eggs!In each egg or sperm there should be ONE copy of each of our chromosomes, BUT in some cases the chromosomes do not divide up evenly and the chromsome pairs do not divide up so that one cell will have TWO copies of the chromsome (instead of one) and another will have NO copies!The result is that at fertilisation the TWO copied chromosome will be added to with the sperm or eggs own copy and make THREE copies of the chromosome! This is calle trisomy! Examples are Kleinfelters where a male will be XXY (extra X), Down Syndrome (Trisomy of chromsome 21)! Edwards Syndrome (trisomy of chromosome 18) Patau syndrome (trisomy of chromosome 13)The total number of chromosomes is 47 not 46In cases with no copies of the chromosome you get cases Turners syndrome (XO) only one X! So the total number of chromosomes will be 45!
Chromosomal disorders are caused by abnormalities in the chromosomes. How does nondisjunction cause chromosome number disorder? swag. What type of
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