The biological process that helps give rise or birth to new organisms from their parents is called reproduction. Each and every organism on the world survives because they have the ability to reproduce and propagate their own kind. There are two broad categories of reproduction. These include asexual reproduction and sexual reproduction. These two methods are used by plants and animals to ensure their species continues to survive. Let us have a look at asexual vs. sexual reproduction and learn the differences between the two.
What is Sexual Reproduction?
Sexual reproduction is a process that usually occurs in most of the complex organisms. This method involves combination of genetic information from the parents and creating a new organism who is the combination of both parents. Sexual reproduction is a very complex process. Here, the organism needs to produce sex cells called gametes. These gametes contain half the number of chromosomes containing information related to all other cells that make up an organism.
The cells undergo meiosis and produce haploid cells (n). These haploid cells contain one copy of genome passed on from the diploid cells (2n). The two copies of the single chromosome cross over each other and form a completely new chromosome. This new chromosome contains a combination genes from both the chromosomes as an effect of crossing over. This ensures, genetic information from both parents is equally passed on to the progeny. Crossing over also ensures the healthy genes remain active in a given population.
Sexual reproduction takes place only after the male and female mate. The males produce sperms and females eggs. The gonads, that is, eggs and sperms are haploid cells. When the sperm fertilizes the egg, it gives rise to a diploid cell containing genetic information from both the parents. The diploid copy of genes favors evolution of a dominant species with less number of mutations and genetic defects. Thus, recombination of genes is very important in masking the recessive traits in organism.
It is possible to observe sexual reproduction in plants. Angiosperms are flowering plants that contain reproductive organs. Some flowers can be hermaphrodites, that is, contain both male and female organs. Few flowers may contain only one of the sexes. These flowering plants undergo pollination where the pollen from the stamen is transferred to the stigma. This pollen like a sperm in animals, travels down the style and fertilizes the eggs in the ovaries. This forms a zygote that will undergo mitosis and form an embryo. This embryo develops into a seed that on germination will develop into a new plant.
In some animals, external fertilization takes place. Here the gametes meet outside the body of both parents. In some animals, like reptiles and birds, a hard covering is formed around the zygote. This is called an egg or shell and the zygote develops outside the female body. Some animals like a kangaroo have a special pouch in the body, for the embryo to grow and develop. In most of the animals, the embryo develops in the female womb.
What is Asexual Reproduction?
Asexual reproduction is the process where only one parent is involved giving birth to a progeny. This progeny produced is totally identical to the parent in its genetic makeup. There are organisms that reproduce asexually like bacteria, multicellular organisms like fungi and even plants. Bacteria divides asexually by binary fission. Hydras and yeast reproduce through binary fission. However, these organisms can undergo sexual reproduction.
For example, bacteria can undergo conjugation, hydra and yeast can reproduce sexually. In some invertebrates, parthenogenesis is the process of reproduction. This means, growth of the embryo or seed can take place without fertilization by a male. This is seen in some parasitic wasps, water fleas, aphids, fish and sharks. Asexual reproduction in plants includes many processes like:
- Internal budding (gemmules)
Pros and Cons of Asexual Vs. Sexual Reproduction
Both these processes involve some advantages and disadvantages. The following paragraphs will discuss both the pros and cons of these processes.
Advantages of Sexual Reproduction
- Sexual reproduction involves two organisms of the same species, thus leading to formation of gamete cells.
- The gametes fuse together causing mixing and combination of the genetic material.
- The recombination of genes helps in increasing the chances of the organism evolving into a healthier and more adaptable species.
- Combination of genes ensures, there is a lesser chance of diseases and defects seen in parents being passed on to their children.
Disadvantages of Sexual Reproduction
- Reproduction cannot occur until and unless gametes from both parents fuse together.
- Only half of the population that is, female species are capable of gestation.
- There is no guarantee that the nucleus of the male gamete will fuse with the female gamete after mating.
- The time taken to produce an offspring by sexual reproduction is very long.
Advantages of Asexual Reproduction
- One parent is needed to complete the process of asexual reproduction.
- In majority of the cases, one is sure an offspring will be produced.
- The gestation period or growth period is very short.
- The offspring has the same phenotype and genetic make up as the parent.
- As there is no cross over or recombination of genes involved, chance of mutation is very less.
Disadvantages of Asexual Reproduction
- As the genetic material from parent is directly passed on to the off spring, it causes all the diseases and defects to be passed on to the offspring as well.
- As no recombination of genes occurs, chances of evolution are very low.
As you can see both these methods have plenty of differences, but both lead to reproduction of progeny. According to the various species, these methods prove to be a successful way to sustain life.