Crossing over occurs at the four-strand stage when two homologous chromosomes, each consisting of a pair of sister chromatids, are paired. Each crossover involves just two of the four strands and generates two recombinant strands.
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Answer: Young rivers are channels that are deeper than they are wide, have a very fast flow, and contain frequent waterfalls and rapids
Answer:
A. A majority of scientists agreed with it
Explanation:
The famous theory called the theory of common descent, states that all the living organisms of the earth have arisen from a common ancestor. This notion was first proposed by a French mathematician,Louis Maupertuis duirng 1740s who was of the view that all organisms had a single ancestor and evolutionary process with the passage of time resulted in the specie diversification.
After that, in 1790s another philosopher Immanuel Kant, suggested that all organisms seem to have a common ancestor. In the same period of 1790s, another scientist , Erasmus Darwin who was the grandfather of Charles Darwin also suggested that all the organisms might have a single ancestor who went through the process of evolution to bring all the majesty into life.
Charles Darwin was the first scientist who worked on this notion for alot of time and proposed the theory of common descent,in his book, On the Origin of Species.
After it, many scientists got agree with this theory such as, Vernon Kellogg in 1907 and T. Ryan Gregory in 2008 and many others explain that no reliable observations exists which contradicts the theory of common descent.
Therefore, option A is the best option.
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There was no life on Earth for the first billion years because the atmosphere was not suitable for life. Earth's first atmosphere had lots of water vapor but had almost no oxygen. Later, frequent volcanic eruptions put several different gases into the air.
