Question

Is crossing over important for the diversity of biological evolution?

Answer 1

Ans. Yes, crossing over (or, genetic recombination) important for – diversity of biological evolution.

# The changes in genetic makeup of an organism may occur due to random mutations (mutations appearing during DNA replication) or through crossing over during meiosis in the parental germs cells. Crossing over increases the genetic variation in population by producing gametes of varied genetic (allelic) makeup. The fusion off such gametes may produce offspring with the combination of traits not previously present in the population. Therefore, crossing-over increases the genetic diversity in population.

# Biological evolution is the summation of changes that have occurred as a result of change in genetic makeup and natural selection.

Simply appearance of a set of traits (say, fast running rabbits of grey-color fur which is difficult to be spotted) that increases the reproductive fitness of species is NOT sufficient for evolution to take place. The change (appearance of a set of traits) must undergo natural selection to exhibit evolution. If the new set of traits is naturally selected in the specified geographical location, the set of traits are said to have evolved. If the set of traits has low reproductive fitness in the specified geographical location, the set of traits is most likely to be eliminated from the population through natural selection of another set of traits with higher reproductive fitness.

# Since numerous combination of genetically-diverse gametes may give rise to several different sets of traits in population, the different set of traits may preferentially may undergo natural selection in different geographical locations. That is, one geographical location exhibits higher reproductive fitness of first set of traits while the other location prefers other set of traits, and so on.

Therefore, by producing gametes of varies genetic makeup, the process of crossing over also provides the path of diversity of biological evolution – the same species exhibits different sets of traits exhibiting natural selection in different geographical area or niche.

# Note that, under normal physiological conditions, the crossing-over only produces different combinations of alleles BUT do NOT produces NEW TRAITS through mutation. Genetic mutations occurs due to intrinsic error of DNA replication machinery (around 1 in around 10⁷ bases) during S-phase of cell-cycle. DNA replication and Crossing-over are two quite different processes.