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.
There are three sources of genetic variation in meiosis: 1) Independent assortment = like shuffling a deck of cards and dealing out half the deck 2) Crossing over = homologous â¦ chromosomes swap parts, making new combinations 3) Random fertilization = only one sperm cell makes it into the egg.he 4 types of genetic variation are 1) mutation-is the mutation of a gene. this is really rare, most mutations are in the recessive trait so they are hidden by a dominant t â¦ rait.