NEET BIOLOGY BY SHASHI SIR

Summary of the main patterns of yolk accumulation and cleavage in animal embryology. I. Holoblastic (complete) cleavage II. Meroblastic (incomplete) cleavage A. Isolecithal (sparse, evenly distributed yolk) 1. Radial cleavage (echinoderms, hemichordates, amphioxus) 2. Spiral cleavage (annelids, most mollusks, flatworms) 3. Bilateral cleavage (tunicates) 4. Rotational cleavage (placental mammals, nematodes, marsupials B. Mesolecithal (moderate vegetal yolk disposition) 1. Displaced radial cleavage (amphibians, some fish [the lampreys, gars and bowfins) A. Telolecithal (dense yolk throughout most of cell) 1. Bilateral cleavage (cephalopod molluscs) 2. Discoidal cleavage (some fish [the hagfishes, chondrichthyans and most teleosts], sauropsids [reptiles and birds], monotremes) B. Centrolecithal (yolk in center of egg) 1. Superficial cleavage (most insects)

With ever -increasing population of the world, enhancement of food production is a major necessity. Biological principles as applied to animal husbandry and plant breeding have a major role in our efforts to increase food production. Several new techniques like embryo transfer technology and tissue culture techniques are going to play a pivotal role in further enhancing food production.  9.1 ANIMAL HUSBANDRY  Animal husbandry is the agricultural practice of breeding and raising livestock. As such it is a vital skill for farmers and is as much science as it is art.  Livestock:  Livestock is commonly defined as domesticated animals raised in an agricultural setting to produce labor and commodities such as meat, eggs, milk, fur, leather, and wool. Animal husbandry deals with the care and breeding of livestock like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats, etc., that are useful to humans.  Extended, it includes poultry farming and fisheries.  Fisheries: