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Lactase persistence or lactose tolerance is the continued activity of the lactase enzyme in adulthood, allowing the digestion of lactose in milk.In most mammals, the activity of the enzyme is dramatically reduced after weaning. [1]
After weaning, in most mammal species, expression of the gene responsible for lactase is way down-regulated, and so production of lactase also goes way down. The majority of humans actually follow this protocol as well, and down-regulate lactase production around 3-5 years of age.
Fishes are a paraphyletic group and for this reason, the class Pisces seen in older reference works is no longer used in formal taxonomy.Traditional classification divides fish into three extant classes (Agnatha, Chondrichthyes, and Osteichthyes), and with extinct forms sometimes classified within those groups, sometimes as their own classes: [1]
Lactase persistence is a rare ability among mammals. [74] Because it involves a single gene, it is a simple example of convergent evolution in humans. Other examples of convergent evolution, such as the light skin of Europeans and East Asians or the various means of resistance to malaria, are much more complicated. [16]
Both mutations, C→T at position -13910 and G→ A at position -22018, have been independently linked to lactase persistence. [27] The lactase promoter is 150 base pairs long and is located upstream of the site of transcription initiation. [27] The sequence is highly conserved in mammals, suggesting that critical cis-transcriptional regulators ...
Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish ().According to FishBase, 33,400 species of fish had been described as of October 2016, with approximately 250 new species described each year.
Prolactin (PRL), also known as lactotropin and mammotropin, is a protein best known for its role in enabling mammals to produce milk. It is influential in over 300 separate processes in various vertebrates, including humans. [5] Prolactin is secreted from the pituitary gland in response to eating, mating, estrogen treatment, ovulation and ...
Lactose, or milk sugar, is a disaccharide composed of galactose and glucose and has the molecular formula C 12 H 22 O 11.Lactose makes up around 2–8% of milk (by mass). The name comes from lact (gen. lactis), the Latin word for milk, plus the suffix -ose used to name sugars.