Asexual vs. Sexual Reproduction

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All forms of life reproduce through one of two means: asexually or sexually. Asexual reproduction involves only one parent with little or no genetic variation, while sexual reproduction involves two parents who contribute some of their own genetic makeup to the offspring, thus creating a unique genetic being.

Asexual Reproduction

In asexual reproduction there is no mating or mixing of genetics. Asexual reproduction results in a clone of the parent, meaning the offspring have identical DNA as the parent.

One way for an asexually reproducing species to get diversity is through mutations at the DNA level. If there is a mistake in mitosis, the copying of the DNA, then that mistake will be passed down to the offspring, possibly changing its traits. Some mutations do not change the phenotype—or observable characteristics—however, so not all mutations in asexual reproduction result in variations in the offspring.​

Other forms of sexual reproduction include:

  • Binary fission: A parent cell splits into two identical daughter cells
  • Budding: A parent cell forms a bud that remains attached until it is able to live on its own
  • Fragmentation: A parent organism breaks into fragments, with each fragment developing into a new organism

Sexual Reproduction

Sexual reproduction occurs when a female gamete (or sex cell) unites with a male gamete. The offspring is a genetic combination of the mother and the father. Half of the offspring's chromosomes come from its mother and the other half come from its father. This ensures the offspring are genetically different from their parents and even their siblings.

Mutations can also happen in sexually reproducing species to further add to the diversity of the offspring. The process of meiosis, which creates the gametes used for sexual reproduction, has built-in ways to increase diversity as well. This includes crossing over when two chromosomes align near each other and swap segments of DNA. This process ensures the resulting gametes are all different genetically.

Independent assortment of the chromosomes during meiosis and random fertilization also adds to the mixing of genetics and the possibility of more adaptations in offspring.

Reproduction and Evolution

Natural selection is the mechanism for evolution and is the process that decides which adaptations for a given environment are favorable and which are not as desirable. If a trait is a favored adaptation, then individuals that have the genes that code for that characteristic will live long enough to reproduce and pass down those genes to the next generation.

Diversity is required for natural selection to work on a population. To get diversity in individuals, genetic differences are required, and different phenotypes must be expressed.

Since sexual reproduction is more conducive to driving evolution than asexual reproduction, much more genetic diversity is available for natural selection to work on. Evolution can happen over time.

When asexual organisms evolve, they typically do so very quickly after a sudden mutation and do not require multiple generations to accumulate adaptations as do sexually reproducing populations. A 2011 study by the University of Oregon concluded that such evolutionary changes take an average of 1 million years.

An example of a relatively quick evolution can be seen with drug resistance in bacteria. The overuse of antibiotics since the mid-20th century has seen some bacteria develop defense strategies and pass them on to other bacteria, and now strains of antibiotic-resistant bacteria have become a problem.