Question

How would the human population be different if crossing over did not happen during meisosis?

Answer 1

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.