What help ensure the survival of a species?
Genetic variation. It is this variation the is the essence of evolution. Without hereditary differences amongst individuals, "survival that the fittest" would certainly not be likely. Either all survive, or every perish.
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During prophase I, chromosomes condense and become visible within the nucleus. As the nuclear envelope begins to rest down, homologous chromosomes move closer together. The synaptonemal complex, a lattice of proteins between the homologous chromosomes, forms at particular locations, dispersing to covering the whole length that the chromosomes. The chop pairing that the homologous chromosomes is referred to as synapsis. In synapsis, the genes on the chromatids the the homologous chromosomes room aligned v each other. The synaptonemal complex also support the exchange of chromosomal segments between non-sister homologous chromatids in a procedure called crossing over. The crossover occasions are the first source of genetic variation produced by meiosis. A single crossover event between homologous non-sister chromatids leader to an exchange that DNA between chromosomes. Following crossover, the synaptonemal facility breaks down and the cohesin connection between homologous bag is additionally removed. In ~ the finish of prophase I, the bag are organized together just at the chiasmata; lock are referred to as tetrads because the four sister chromatids of each pair the homologous chromosomes are currently visible.
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