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Biological systems use different forms of reproduction to accomplish different tasks. This article addresses sexual reproduction and its role in genetic variability.

Introduction

While many of us choose not to think about this fact, we as humans are all products of sexual reproduction. This means that our parents likely engaged in the act of sex in order to procreate, or produce a child.

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Though this activity in humans is often understood in terms of the basics, it is often difficult to understand the complexity of sexual reproduction and the key characteristics that make this process so important. Let’s discuss sexual reproduction, and identify some key aspects of this process.

Sexual Reproduction: A Necessary Life Process

There are several characteristics that organisms must possess in order to be considered living. Of these characteristics, reproduction is probably one of the least understood.

Reproduction is the process by which an organism produces offspring for the perpetuation of a species. There are two basic categories of reproduction: asexual and sexual.The goal of asexual reproduction is to simply increase the population of a particular organism. This is often seen in bacteria, fungi, and even some lower animals, such as insects. In this process, the offspring are typically identical clones of the parent or very similar to the parent genetically.

Sexual reproduction, however, is different in that the primary goal is to increase genetic variability. This means that sexual reproduction is necessary so that the offspring will have different combinations of genetic traits than the parents.So here’s the obvious question: why do we need genetic diversity? That answer is still being researched to this day, but most scientists can agree that genetic diversity is important for protecting animal species and for the process of evolution. Let’s imagine for a second that all humans are identical in terms of genetic makeup. If a disease were to affect one individual in the group, then the entire group would be susceptible to that illness, and the entire population could be wiped out instantly. Instead, genetic variability allows for some individuals to have a different set of traits, and those different combinations may actually protect some of the individuals from mass extinction.In short, through sexual reproduction, genetic variability improves the chances of species survival.

Different Forms of Sexual Reproduction

Many organisms engage in sexual reproduction, though the methods by which they achieve this process vary. However, the goal for every method is to increase genetic diversity as a means of perpetuating the species.

Bacteria

Have you ever heard of bacteria becoming medically resistant? What about bacteria that are incurable, or difficult to treat? Well, bacteria are single-celled organisms that use sexual reproduction to exchange genes prior to asexual reproduction. Through the exchange of plasmids (circular pieces of DNA) bacteria can give each other new genes and new traits, such as antibiotic resistance. When those bacteria undergo asexual reproduction, the newly formed generations now have copies of that new DNA.

While asexual reproduction is how bacteria increase their population size, their ability to develop resistance and survive comes from the sexual reproduction portion of their life cycles.

Bacterial Sexual Reproduction
Bacterial conjugation

Invertebrates

Some invertebrates also use a combination of asexual and sexual reproduction in order to perpetuate the species. For example, Aurelia jellies (Moon jellyfish), undergo sexual reproduction as adults to produce planulae (first-stage offspring). These offspring are genetically a combination of genes from the male and female adult jellies. However, these planulae will eventually form polyps and, in this stage, asexually reproduce to create multiple copies of the DNA from the planulae.

While each of the offspring from the polyp will be identical to the others, the sexual reproduction portion ensures that the offspring will be different from the adults.

Humans

In humans, sexual reproduction is the sole means by which we biologically reproduce. (For the sake of this article, we will not address biological engineering, cloning, or in vitro methods.) Through coitus, or intercourse, males deposit sperm cells into the reproductive tract of the female. After deposition, the sperm cells swim towards the egg, and when one cell fertilizes the egg, it becomes a zygote.

In this process, the zygote receives half of its genetic information from the mother, and half from the father. This means that the child that is produced from this process will have a genetic combination that is different from both parents, but will contain genes donated from each parent. Because humans tend to have stable life cycles, and are not as prone to short life spans as some other organisms, we do not engage in asexual reproduction for population purposes.

Fertilization of an Egg by a Sperm Cell
fertilization

Lesson Summary

Sexual reproduction is a vital process for the survival of organisms, including humans.

Through the exchange of genetic material, and the diversification of gene combinations in offspring, organisms can ensure survivability in an ever-changing world. Without sexual reproduction, it would be a matter of time before many of the organisms on the planet experience massive extinction. Keep that in mind the next time you see a cute infant. That child is the result of one of nature’s most critical processes.

Learning Outcomes

Upon the conclusion of this lesson, rate your ability to easily:

  • Discuss the two basic categories of reproduction
  • Interpret the meaning of asexual reproduction and compare it to sexual reproduction
  • Recognize various forms of sexual reproduction
x

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