Secretion of human chorionic gonadotropin [HCG] only occur during pregnancy in the placenta. The concentration of this hormone increase rapidly during the first three months of pregnancy; the amount in the blood stream doubles every two to three days as the development of the placenta and embryo progress. The hormone reaches its maximum concentration peak around the sixth week of pregnancy and after this, its concentration decline.
During binary fission in a bacterial cell, a base pair is changed from adenine to cytosine due to a random mutation.
Binary fission is a type of asexual reproduction through which a bacteria divides and its body is separated into two new bodies.
If during binary fission in a bacterial cell, a base pair is changed from adenine to cytosine, it is because of a random mutation. A mutation is a genetic alteration or a change in the DNA sequence which results in the generation of a variant. Mutations in the DNA sequence which occur without any specific pattern is known as a random mutation.
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Answer: More than 99 percent of all organisms that have ever lived on Earth are extinct. As new species evolve to fit ever changing ecological niches, older species fade away. But the rate of extinction is far from constant. At least a handful of times in the last 500 million years, 75 to more than 90 percent of all species on Earth have disappeared in a geological blink of an eye in catastrophes we call mass extinctions.
Though mass extinctions are deadly events, they open up the planet for new forms of life to emerge. The most studied mass extinction, which marked the boundary between the Cretaceous and Paleogene periods about 66 million years ago, killed off the nonavian dinosaurs and made room for mammals and birds to rapidly diversify
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