he embryo develops. In many sea creatures, eggs and sperm are simply cast into the environment on a synchronous cue. However, in all these forms, the simple gonad is the organ producing all of the gametes.
Example #2: Earthworms
While it may seem like the above plan of sexual dimorphism is the only way to go, there are many organisms that exist with both male and female gonads. The most common of these is the typical earthworm. A single earthworm contains a male gonad and a female gonad. The male gonad may give gametes to another worm, and the female gonad can take gametes from the same worm.
One theory is that this gives earthworms an added benefit when mating because it allows the passage of genetics to go both ways. This is important to animals that may rarely meet underground, though they might only be inches from each other. This way, not 1, but 2 mating events can occur every time a pair of earthworms meet. Oftentimes it is necessary in organisms that are immobile, have poor senses, or travel individually to develop other means for reproducing successfully. This is often seen in the gonad of the animal becoming specialized in some way. In earthworms it can be seen as the possession of both types of gonad.
Example #3: Wrasses
The wrasse is a common coral-reef dwelling fish, of which there are many species. Certain species have become what are known as sequential hermaphrodites. While all individuals possess both male and female gonads, only one individual looks unlike the others. In this individual, the now dominant female, her male gonad is suppressed, and her female gonad is active. She produces the eggs for the whole group, and the smaller fish fight to fertilize them.
The smallest fish, now male, will eventually become the largest and oldest of the males. At that time, if the female dies, it will be his turn to assume the role of head female. As such, he will undergo a sexual metamorphosis in which his male gonad is suppressed and his female gonad is activated. The new female often becomes a different color and grows rapidly, probably in response to the quick change of hormones. This sequential hermaphroditism can be seen many fishes including clown fish and wrasses, as well as in some reptiles.
Related Biology Terms
- Diploid – A cell with the full number and pairs of chromosomes for a given species.
- Haploid – A cell with the full number of chromosomes, but none of the pairs, for a given species.
- Gamete – A haploid cell produced by a gonad in many organisms.
- Sexual-dimorphism – When two organisms of the same species look or function differently based on gender.
1. What is the function of a gonad?
A. To clean the blood of toxins.
B. To produce and regulate hormones.
C. To create gametes, or haploid cells.
D. Some of B and C.
2. Congrats! You found a new species. Now you have to describe it for Science! When watching the organism reproduce, you notice that the individuals mating look the same. There is usually one mating that happens, then both individuals give birth to an offspring. Without killing to creatures to look inside at their gonads, how would you describe them?
C. Sequentially Hermaphroditic.
3. Inside of a gonad, cells that have undergone meiosis often reside close to cells that have not underdone meiosis yet. If you take a cross-section of a gonad, and look at it under the microscope, you can see two cells close to each other, the first has twice as much DNA as the second cell. How do we describe the amount of DNA, scientifically?
A. First Cell: Haploid; Second Cell: Diploid
B. First Cell: Diploid; Second Cell: Haploid
C. First Cell: Duplicated; Second Cell: Singular