Answer:
The Crainum fossils are the youngest fossils from 134 million years ago. The occur in the top layer of the earth's crust (rock)
Explanation:
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Transcription is the transfer of genetic information from DNA to RNA, and it happens in the nucleus. We can automatically rule out B. B is incorrect because it doesn't make sense; how can a process stop before it even begins?
A. I believe this is incorrect because mRNA is involved when the genetic information needs to leave the nucleus. mRNA would take it to a ribosome outside of a nucleus. Since transcription happens in the nucleus, mRNA is irrelevant before it starts.
C. This doesn't really make sense. mRNA carries information from the DNA, but not vice versa (in these early stages).
D. This would make the most sense, since RNA polymerase needs to attach to the promoter on the strand before transcription can begin.
Answer is A. A population becomes separated by environmental factors into two groups that do not reproduce with one another.
When a population of a species become geographically separated then gene flow between them stops. Over a period of time, the population may become genetically different in response to the natural selection due to different environments. Selection and genetic drift will act differently on these two separated populations. This will results into two separate species. This type of speciation is called allopatric speciation.
DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). <span>DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.</span>
