Malcolm X a Homemade Education
Elizabeth Terry
Biology 101-06
MWF at 3:00
November 14, 2011
Research paper
DOWN SYNDROME
Down syndrome is the most common cause of mental retardation Down syndrome is the most common cause of mental retardation. It is caused by the presence of an extra chromosome. Chromosomes contain sequences of DNA called genes that represent the genetic information that exists within a cell. Twenty-three distinctive pairs of chromosomes which is 46 in total. They are located within the nucleus (a region of the cell that is bounded by a specialized membrane, and which houses the genetic material). When a sperm cell fertilizes an egg cell, the newly created zygote normally receives 23 chromosomes from each parent. The contribution of genetic information from each parent is what makes each baby a distinctive blend of both characteristics. In Down syndrome a mistake during division of the sperm or egg cell produces a cell with an extra chromosome 21. This event occurs during cell division and is referred to as nondisjunction, or the failure of all chromosomes to separately properly resulting in retention of one of the chromosomes in one of the two new daughter cells. This is also called trisomy 21 and is accounted for 95% of all Down syndrome patients. A rare number of Down syndrome cases the original egg and sperm cells begins with the correct number of chromosomes but shortly after fertilization during the phase where cells are dividing rapidly a single cell can divide abnormally creating a line of cells with an extra chromosome 21.It’s called a cell line mosaicism. The individual with this type of down syndrome has two types of cells: some 46 chromosomes which is the normal number and some with 47. Individuals who are mosaic for trisomy 21 typically have less sever sign and symptoms of the disorder. Another are location that can cause down syndrome is called a chromosome translocation. This is an even that unlike the numerical abnormally causing trisomy 21, there
Biology 101-06
MWF at 3:00
November 14, 2011
Research paper
DOWN SYNDROME
Down syndrome is the most common cause of mental retardation Down syndrome is the most common cause of mental retardation. It is caused by the presence of an extra chromosome. Chromosomes contain sequences of DNA called genes that represent the genetic information that exists within a cell. Twenty-three distinctive pairs of chromosomes which is 46 in total. They are located within the nucleus (a region of the cell that is bounded by a specialized membrane, and which houses the genetic material). When a sperm cell fertilizes an egg cell, the newly created zygote normally receives 23 chromosomes from each parent. The contribution of genetic information from each parent is what makes each baby a distinctive blend of both characteristics. In Down syndrome a mistake during division of the sperm or egg cell produces a cell with an extra chromosome 21. This event occurs during cell division and is referred to as nondisjunction, or the failure of all chromosomes to separately properly resulting in retention of one of the chromosomes in one of the two new daughter cells. This is also called trisomy 21 and is accounted for 95% of all Down syndrome patients. A rare number of Down syndrome cases the original egg and sperm cells begins with the correct number of chromosomes but shortly after fertilization during the phase where cells are dividing rapidly a single cell can divide abnormally creating a line of cells with an extra chromosome 21.It’s called a cell line mosaicism. The individual with this type of down syndrome has two types of cells: some 46 chromosomes which is the normal number and some with 47. Individuals who are mosaic for trisomy 21 typically have less sever sign and symptoms of the disorder. Another are location that can cause down syndrome is called a chromosome translocation. This is an even that unlike the numerical abnormally causing trisomy 21, there