What is Cross Fertilization?
To understand the cross fertilization meaning let us first begin by understanding fertilization. Cross fertilisation is a term referring to the reproduction among the plants. Fertilization is a sexual reproduction process in plants that occurs after pollination which is pollen production that represents the male contribution in the process and germination. The fusing of male gametes which are the pollen grains and female gametes ovum to generate a diploid zygote is known as fertilisation. It is a physicochemical reaction and it occurs only after the carpel has been pollinated. Since there are many types of flowering plants there are different types of fertilization as well. Let us go ahead and understand the definition and meaning of each type of fertilization and find answers.
Who Discovered Fertilization?
Strasburger discovered in 1884 that the vegetative nucleus and two male nuclei are discharged into the embryo sac by the pollen tube. He disclosed for the first time the fusing of one of the male nuclei with the egg nucleus in this landmark study on Monotropa hypopitys, demonstrating fertilisation in higher plants. And thus the world came to understand the possibility of the existence of many types of fertilization.
Fertilization and Its Types
Self-fertilization - is the process of pollen being transferred to the stigma of the same flower and this is also referred to as autogamy.
Internal Fertilization Definition - Internal fertilisation is used by most sexual plants to reproduce. The ovary is where sperm and egg meet in plants. Pollen produces sperm, which is small and light and can travel by air or water. Plants, on the other hand, can develop sex organs that help sperm and egg meet.
External Fertilization - External fertilisation is commonly performed in water or a moist environment and fertilisation as the name suggests occurs outside the plant body. The moist environment helps to facilitate the movement of sperm or pollen to the ovum. Spawning is the release of eggs and sperm into the water and most of the external fertilization examples in plants include the ones that reside in water bodies. The benthic plants are the most common external fertilization examples and are prominently viewed and studied.
Double Fertilization - Is where after the fertilization the zygote is divided into two cells as the female fuses with two male gametes and hence the name double which is an uncommon phenomenon.
Cross Fertilization - Pollen grains are transferred from one flowers’ anther to another’s stigma. This happens when two blossoms on different plants interact. And it happens often when flowers with diverse genetic backgrounds come together.
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This image explains the concept of cross-pollination that leads to cross fertilization in a simple manner.
Self- Fertilization Versus Cross Fertilization
The main difference between the self-fertilization and cross fertilization is the pollination process, which results in many different types of breeds and results and that keeps on changing as the years go by.
Benefits or Advantages of Cross Fertilization
Cross-pollination during the cross fertilisation process causes genetic recombination, which results in the emergence of new types.
Due to hybrid vigour, the offspring produced through cross-fertilization are healthy and stronger.
If only cross-fertilization is allowed or practised and self fertilization is avoided in a variety of crop plants like sunflower, mustard, and clover, they produce larger yields.
Among the types of fertilisation, this is the superior one because via this the disease resistant plant is originated.
Inbreeding depression can be avoided.
Cross Fertilization Disadvantages
Because cross fertilization is dependent on the agents, there is always some unpredictability.
From an economic standpoint, cross fertilization is not advantageous. Plants lose a lot of energy on numerous contraptions required for cross fertilization, and pollen grains are wasted in the process.
Despite its drawbacks, cross fertilization is nevertheless favoured by nature. In fact, plants have a variety of mechanisms to encourage cross fertilization while limiting self fertilization. The reason for supporting cross fertilization is mainly due to the production of healthier offspring.
Conclusion
Even though the agents carrying out the pollination process are the same as the wind, water, bees and other insects, bats and birds and other animals which are herbivores and graze on them, the consequences are so different for the pollination within the flowers or of the same plant and the flowers of different plants. Cross fertilization plays a vital role in maintaining the gene pool and creating hybrids that are disease resistant and from there on a healthy gene pool is created again. Even though the process takes a toll in every way the results are remarkable and worth all the energy and time consumed. Even though it is a natural process the man has been curating this phenomenon in recent years and the consequences are great despite the taxing ways of contemplating over which flowers of which plant must be crossbred. There is no other method that has been continued for so long and has evolved many healthy variants and there is no stopping this wonderful phenomenon anytime soon.
FAQs on Cross Fertilization
1. What is cross-fertilization in biology?
Cross-fertilization, also known as allogamy, is a mode of sexual reproduction where the gametes (e.g., pollen and ovule in plants) from two separate individuals fuse to form a zygote. This process requires the transfer of male gametes from one parent to the female gametes of another parent, resulting in offspring with a genetic makeup different from both parents.
2. How is cross-fertilization different from self-fertilization?
The primary difference lies in the source of the gametes and the resulting genetic diversity.
- Source of Gametes: In cross-fertilization, gametes come from two different individuals. In self-fertilization (autogamy), gametes from the same individual fuse.
- Genetic Variation: Cross-fertilization significantly increases genetic variation by combining genes from two different parents. Self-fertilization produces offspring that are genetically very similar or identical to the single parent, limiting variation.
3. What are the main advantages of cross-fertilization for a species?
Cross-fertilization offers several evolutionary advantages, including:
- Increased Genetic Diversity: It introduces new gene combinations into the population, which is crucial for adaptation to changing environments.
- Hybrid Vigour: Offspring produced through cross-fertilization, known as hybrids, are often stronger, healthier, and more vigorous than their parents.
- Disease Resistance: The genetic recombination can create new combinations of alleles that provide resistance to diseases and pests.
- Masking Recessive Alleles: Harmful recessive traits are less likely to be expressed as they can be masked by a dominant allele from the other parent.
4. Are there any disadvantages or limitations to cross-fertilization?
Yes, despite its benefits, cross-fertilization has some limitations. It is highly dependent on external pollinating agents like wind, water, or animals, making the process uncertain. Plants often have to produce a large amount of pollen to ensure success, which is energetically costly. Furthermore, there is a risk of losing desirable traits if cross-pollination occurs with a genetically inferior individual.
5. Why have many plants evolved complex mechanisms to specifically favour cross-fertilization?
Plants have evolved mechanisms to favour cross-fertilization primarily to avoid inbreeding depression, a condition where continued self-fertilization leads to a reduction in fitness, health, and fertility over generations. By promoting the fusion of gametes from different plants, they ensure a constant shuffling of genes. This genetic diversity is the key to a population's ability to survive environmental changes, fight off new diseases, and maintain overall vitality.
6. Can any two different plant species be cross-fertilized? Explain the concept of compatibility.
No, successful cross-fertilization cannot occur between any two plant species. The process is governed by pollen-pistil interaction, which is a form of genetic compatibility check. The stigma of a flower can recognise and accept pollen from the same species while rejecting pollen from a different, incompatible species. This ensures that fertilization only happens between genetically compatible individuals, preventing the formation of non-viable or sterile offspring.
7. How is the principle of cross-fertilization applied in agriculture?
In agriculture and horticulture, cross-fertilization is the basis for artificial hybridization. Farmers and scientists manually transfer pollen from a plant with desirable traits (e.g., high yield) to the stigma of another plant with different desirable traits (e.g., disease resistance). This controlled cross-fertilization allows them to create new hybrid varieties that combine the best qualities of both parents, leading to improved crop quality and productivity.
8. Besides plants, does cross-fertilization occur in animals?
Yes, cross-fertilization is the standard mode of reproduction for the vast majority of animal species, including humans. Even in hermaphroditic animals (those with both male and female reproductive organs), like the earthworm, cross-fertilization is preferred. Two earthworms will exchange sperm to fertilize each other's eggs, ensuring they do not self-fertilize and thus maintain genetic diversity within their population.
