Answer:
A rapidly changing environment
Explanation:
The sexual reproduction is more advantageous to organism to survive in the harsh conditions due to the changes in the sequence of nucleotides of the genes which became a characteristic feature of the sexual mode of reproduction.
This process of changes in the sequence is known as recombination. The sexual mode or reproduction evolved in the last common ancestors of eukaryotes but it is known to occur in the prokaryotes also as they reproduce by conjugation, transformation and transduction.
The sexual mode of reproduction was evolved in the organism as a result of the change in the environment to survive and thrive in the environment.
Answer:
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<span> Evolution is referred to as a theory because it is a well- supported explanation of phenomena that have occurred in the natural world.</span>
When studying a complex biological phenomenon, it is required to look at the workings of the various systems associated with it. The research is a top-down approach of getting down to the very detail of the cells and molecules taking part in it. Example, a person finds it difficult to digest milk and vomits it on ingestion. As we go a level down, we identify the systems getting affected by the milk. Then, further down, the cells that take in digesting the milk are identified. The enzymes that break down the substances in the milk are identified. The gene regulation of this enzyme (lactase) is studied to check its regulation. This work of doing a top-down approach to find the signalling pathway within the cells to identify the problem with the working of lactase to digest milk, is a necessary approach.
The formation of the fertilization envelope requires an increase in the cytosolic concentration of calcium ion .
<h3>What is fertilization?</h3>
The process of union of a haploid male gamete or sperm with a haploid female gamete or ovum to form a diploid cell ,zygote ,is called fertilization .
In human fertilization is internal as it takes place in the fallopian tube .
During coitus male discharge sperm to the vagina of the female , from the vagina sperm reach the ampulla partly by the movement of their tails and partly by the action of uterus .
After completing this long travels sperm reaches the fallopian tube within five minutes .
Learn more about fertilization here:
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