Suppose polymerase chain reaction (pcr) is used to amplify a single dna marker on human chromosome 21. further suppose that a couple who have a child with down syndrome (trisomy 21) is examined for this marker. the mother has marker alleles of 310 and 380 bp. her mate has marker alleles of 290 and 340 bp.

Mitochondria, the organelles involved in cellular respiration, can also generate chemicals called reactive oxygen species (ROSs). ROSs can damage mitochondria. Damaged mitochondria generate more ROSs than healthy mitochondria. This is an example of a positive feedback mechanism

The reactive oxygen species that are given out by the mitochondria during cellular respiration are the major cause of aging. Though this has a lot of negative effects but this also has a small amount of positive effects such as the start of angiogenesis or cell proliferation.