Where does DNA come from? What is DNA? What is a Trisomy? DNA comes from our parents, we get half from mom and the other half from dad. DNA is two strands of nucleotide bases coiled into a double helix. The four nucleotide bases are Adenine, Thymine, Cytosine, and Guanine. Adenine pairs with Thymine and Guanine pairs with Cytosine. Each set has 23 single chromosomes- 22 Autosomes and one X or Y sex chromosome. (Massimini, 2000). “Your mother can give you only an X chromosome, but your father can pass on an X or a Y chromosome. If you receive an X chromosome from your father, the XX pair makes you genetically a female. If you receive a Y chromosome from your father, then your XY pair you're genetically a male (mayoclinic). Trisomies occur when there is an extra chromosome. An example of this would be, we have a total of 46 chromosomes (23 from each parent). When one extra is added this is a trisomy because now there’s 47 chromosomes. “There are two different forms of trisomy they are as follows: Partial Trisomy- part of a chromosome attaches itself to another chromosome, and Mosaic Trisomy- every cell contains extra” (Massimini, 2000, p.48).
DNA replication is when cells make copies before they divide. DNA is held together by Hydrogen bonds. Hydrogen bonds are broken by an enzyme and DNA polymerase makes a complementary strand of each parent strands. DNA polymerase moves along the strand of DNA, and uses the bases as a template to make a new strand of DNA. It matches A with T and G with C as it moves along the strand. DNA liagase is the glue that seals any gaps holding the new strand together. DNA polymerase proof reads its work and corrects any mistakes it finds. If a mistake goes uncorrected the error will become a mutation, causing non-disjunction which causes many different forms of different trisomies ( Starr, Evers, and Starr, 2009).
In recessive genes, both parents carry one normal gene and one altered gene. “In dominant genetic disorders, if one affected parent has a disease- causing gene that dominates its normal counterpart, each child in the family has a 50% chance of inheriting the disease gene and the disorder” (Massimini, 2000, p.7). Meiosis is the production of sex cells. “Meiosis involves two cycles of cell division (Meiosis 1 and Meiosis 2) and produces four cells each of which contains 23 individual chromosomes”( Martini, Nath, and Bartholomew, 2012, p.1038). At the end of this cycle, you will have four daughter cells. During Prophase 1, the chromosomes will crossover. This happens to make new combinations of parental Alleles. The more crossing over that takes place the more the child will look like that parent or grandparent. The child will express more of their genes.
Most causes of abnormalities are due to non-disjunction. This is when “one or more pairs of chromosomes do not separate properly during mitosis or meiosis” ( Starr, Evers, and Starr, 2009, p.72). Non-disjunction usually rises with the mother’s age. In...