If crossing over did not occur during meiosis, there would be less genetic variation within a species. With crossing over, potentially every chromosome could consist of a combination of both maternal and paternal alleles, which, along with random segregation of chromosomes during anaphase II, would result in a nearly limitless number of genetic variations between related individuals and within a species.
Without crossing over, each chromosome would be either maternal or paternal, greatly reducing the number of possible genetic combinations, which would greatly reduce the amount of genetic variation between related individuals and within a species. And as genetic variation decreases, the species has a very less chance to evolve and adapt as natural selection.
The above statement is False. If the concordance rate for a given trait is 10 % for both identical and fraternal twins, it means that genes play a relatively minor role in the development of this trait, whereas environment plays a major role in the appearance of this trait.
