Asexual Versus Sexual Reproduction

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  1. 0:25 Asexual Reproduction
  2. 1:20 Sexual Reproduction
  3. 2:54 Meiosis
  4. 4:03 Lesson Summary
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Taught by

Greg Chin

Did you know that some organisms can reproduce without a mate? Check out this video lesson on asexual versus sexual reproduction to discover the different ways organisms can reproduce and the main differences between mitosis and meiosis.

Why Meiosis?

Mitosis gives organisms the ability to create new cells. In the case of many organisms, like us, it provides the opportunity to become multicellular. However, for other organisms, like yeast, mitosis is a means of reproduction.

Asexual Reproduction

If an organism uses mitosis as a means of reproduction, it is said to be reproducing asexually. Asexual reproduction is also known as vegetative reproduction. As we've seen, mitosis is designed to faithfully create two daughter cells with genomes that are identical to the mother cell. Each new cell is a clone of the original cell.

In asexual reproduction, cells divide by mitosis and result in two identical cells
Asexual Reproduction

Asexual reproduction is an effective strategy for many organisms. It is highly efficient because a mate is not required. And the cost to the parent in time and energy is low because there's no progeny to rear.

However, this strategy offers little, if any, opportunity for variation in the genetic makeup of asexually reproducing organisms. Since all of the individuals in a given population of asexually reproducing organisms are clones, they share the same weaknesses. Therefore, the entire population could perish if a major environmental change occurred.

Sexual Reproduction

An alternative strategy, known as sexual reproduction, offers an opportunity to introduce genetic variation into the population. During sexual reproduction, offspring are produced from the genetic material of two different individuals: the offspring's mother and father.

Each parent contributes half of the genetic material the offspring requires in the form of a gamete cell. Recall that a gamete is a specialized sex cell produced by each parent for sexual reproduction. The female provides an egg, which is fertilized by a male sperm cell. During fertilization, the haploid male and female gametes fuse to form a single diploid cell, which can then go on to produce the rest of the cells in a multicellular organism via mitosis.

However, where do all these gametes come from? Mitosis won't do us any good if we're starting with a diploid cell because mitosis will only allow us to make more diploid cells. And, the gametes have to be haploid because if we fuse diploid cells together, we'd end up with a cell with too many chromosomes. To solve this problem, sexually reproducing organisms have evolved a second specialized type of cell division known as meiosis.

Meiosis is a type of cell division that evolved in sexual reproduction to produce haploid cells
Meiosis Produces Gametes

Strategy for Meiosis

The purpose of meiosis is to produce cells with half of the normal genetic content found in the organism. Because meiosis and mitosis are both types of cell division, they share many similar structures and strategies.

For instance, DNA replication precedes both types of division. Chromosome condensation and a spindle apparatus are key strategies for maneuvering chromosomes in each case. However, unlike mitosis, which makes two cells that are exact copies, the primary goal of meiosis is to reduce the number of chromosomes in the cell by half.

If a diploid organism has two copies of each chromosome, they've got one from mom and one from dad. That means each parent had to put only one copy each chromosome into its gamete. For instance, mom donates one of her copies of chromosome one and so does dad. The same is true for chromosome two, three, four and so on.

In sexual reproduction, each parent contributes one copy of each chromosome to the gamete
Each Parent Contributes One Copy of Each Chromosome

But this raises another question. We currently have no way of identifying homologs and ensuring that each cell gets one copy. How can an organism achieve this goal? As we will see, nature's answer to this question not only makes meiosis possible but also will have significant consequences for the inheritance of genetic information.

Lesson Summary

In summary, asexual reproduction is a form of reproduction from a single parent based on mitosis. Sexual reproduction is a form of reproduction in which offspring are produced from the union of gametes from two genetically different parents. A gamete is a specialized sex cell produced by each parent for sexual reproduction. Meiosis is a specialized type of cell division which produces gamete cells for sexual reproduction.

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