Esophagus. Esophageal spasms are painful muscle contractions that affect your esophagus, the hollow tube between your throat and your stomach. Esophageal spasms can feel like sudden, severe chest pain that lasts from a few minutes to hours.Esophageal spasms usually occur only occasionally. But for some people, the muscle contractions are frequent and can prevent food and liquids from traveling through the esophagus.Esophageal spasms can lead to chronic pain and swallowing problems. Treatment for occasional esophageal spasms may not be necessary.sophageal spasms usually occur only occasionally. But for some people, the muscle contractions are frequent and can prevent food and liquids from traveling through the esophagus. Esophageal spasms can lead to chronic pain and swallowing problems.
Random mutations are the ultimate source of genetic variation. Mutations are likely to be rare and most mutations are neutral or deleterious, but in some instances the new alleles can be favored by natural selection.andom mutations are the ultimate source of genetic variation. Mutations are likely to be rare and most mutations are neutral or deleterious, but in some instances the new alleles can be favored by natural selection.
Crossing over in meiosis results in genetic recombination, which is responsible for the genetic diversity of a population. Genetic recombination and natural selection are the driving forces behind evolution. It causes most of the differences between parents and their offspring and differences between siblings.