Deletion occurs when an end of a chromosome breaks off or when two simultaneous breaks lead to the loss of an internal segment. Causes skin to age prematurely. Duplicated is the presence if a chromosomal segment more than once in the same chromosome. This may cause problems with health, development, or growth. Inverted has occurred when a segment of a chromosome is turned around 180 degrees. This may cause problems in their physical and or intellectual development. Translocation is the movement of a chromosome segment from one chromosome to another non-homologous chromosome. Many cause problems with distinctive facial features and cancers.
The sequence of amino acids in a protein is determined by the sequence of nucleotide bases in the stretch of DNA that encodes the protein. Each amino acid is represented by a sequence of three DNA bases, called a triplet. Because 4 different bases can be combined into 64 different triplets, most of the 20 amino acids are represented by more than 1 triplet. The DNA nucleotide combination A-T-G (adenine-thymine-guanine) always codes for the amino acid methionine, regardless of where it may appear within the overall DNA coding sequences of different proteins During the first stage of gene expression, which is called transcription, an mRNA molecule is produced that is an exact copy of the relevant DNA region. To produce this molecule, the DNA double helix untwists temporarily, exposing the base sequence that encodes the protein to be synthesized. One of the two DNA strands serves as a template for the formation of the mRNA, which is generated with the help of a host of enzymes and regulatory molecules. As in the DNA, three-base sequences specify which amino acids will later be used when the protein is assembled; these RNA triplets are called codons. The initial mRNA molecules undergo further processing in the nucleus to