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The underlying theme of the essay is the need to teach biological evolution in the context of debate about creation and evolution in public education in the United States. [5] The fact that evolution occurs explains the interrelatedness of the various facts of biology, and so makes biology make sense. [ 6 ]
This can introduce genes into a population that were not present before. [24] Evolution is not a random process. Although mutations in DNA are random, natural selection is not a process of chance: the environment determines the probability of reproductive success.
DNA can be copied very easily and accurately because each piece of DNA can direct the assembly of a new copy of its information. This is because DNA is made of two strands that pair together like the two sides of a zipper. The nucleotides are in the center, like the teeth in the zipper, and pair up to hold the two strands together.
Human chromosome 2 was created from a fusion of two chimpanzee chromosomes and still contains central telomeres as well as a vestigial second centromere. Polyploidy , especially allopolyploidy, which occurs often in plants, can also result in reproductive incompatibilities with parental species.
Homosexuality is prevalent across human societies, past and present. These facts constitute an evolutionary puzzle. [26] [non-primary source needed] Decline in average human body temperature since the 19th century: Medical data suggests that the average body temperature has declined 0.6 °C since the 19th century. The cause is unclear although ...
Deoxyribonucleic acid (DNA) is a nucleic acid containing the genetic instructions used in the development and functioning of all known living organisms. The chemical DNA was discovered in 1869, but its role in genetic inheritance was not demonstrated until 1943. The DNA segments that carry this genetic information are called genes.
Some types of non-coding DNA are genetic "switches" that do not encode proteins, but do regulate when and where genes are expressed (called enhancers). [30] Regulatory sequences have been known since the late 1960s. [31] The first identification of regulatory sequences in the human genome relied on recombinant DNA technology. [32]
Cell walls may or may not be present. The eukaryotic DNA is organized in one or more linear molecules, called chromosomes, which are associated with histone proteins. All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. [2] Some eukaryotic organelles such as mitochondria also contain some DNA.