Answer:
a. a portion of the population becomes isolated from the remainder of the population and experiences different selective pressures
Explanation:
This is an example of allopatric speciation Allopatric speciation is a form of speciation (formation of new species) that occurs as a result of geographic isolation. This means that a part of population becomes physically separated from the initial main population. There is no gene flow between these two populations and as a result the two populations reach a high level of genetic divergence. They can no longer interbreed which means they become two different species (speciation).
New populations evolve as result of mutation, genetic drift and natural selection.
For example, Galapagos finches are isolated from others by the ocean (geographic isolation). Because of the isolation, the finches don’t breed with one another. So, they developed unique characteristics and became endemic.
Pituitary dwarfism is caused by problems arising from the pituitary gland. The pituitary gland, also called the hypophysis, is a gland at the base of the brain that produces many different hormones. This gland is divided into the anterior (front) and posterior (back) halves. The anterior pituitary produces six hormones: growth hormone, adrenocorticotropin (corticotropin), thyroid stimulating hormone (thyrotropin), prolactin, follicle stimulating hormone, and lutenizing hormone. The posterior pituitary gland only produces two hormones: antidiuretic hormone (vasopressin) and oxytocin.
The growth process begins in the lower part of the forebrain in a small organ called the hypothalamus. The hypothalamus releases hormones that regulate the production of other hormones. When the hypothalamus releases growth hormone-releasing hormone (GHRH), the anterior pituitary is stimulated to release growth hormone (GH). Growth hormone then acts on the liver and other tissues and stimulates them to secrete insulin-like growth factor-1 (IGF-1). IGF-1 directly promotes the development of bone and muscle, causing bones to grow in length, and muscles to increase protein synthesis (make more protein).
Since growth is a complex phenomenon, it may be slowed down or stopped by abnormalities arising at any point in the process. Thus, dwarfism can result if there is a deficiency in any of these hormones, if there is a failure in the receptor cells receiving the hormonal stimuli, or if the target cells are unable to respond.
At its most basic, pituitary dwarfism results from decreased production of hormones by the anterior pituitary. When none of the hormones of the anterior pituitary are adequately produced, this is called panhypopituitarism. A common form of pituitary dwarfism is due to deficiencies in the production of growth hormone (GH). When less GH than normal is produced during childhood, an individual's arms, legs, and other structures continue to develop in normal proportions, but at a decreased rate.
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Answer:
Eukaryotes are organisms made out of eukaryotic cells, cells with a membrane-bound nucleus and membrane-bound organelles.
Prokaryotes differ from eukaryotes in that their cells do not contain a membrane-bound nucleus that contains their DNA.
Explanation:
