Anjali Mishra Content Writer-SME
Content Writer-SME
Apomixis is defined as a type of asexual reproduction in which the formation of seeds takes place without fertilization. It is derived from the Greek words ‘apo’ means away from and ‘mixis’ means ‘mixing’. In plants, it mimics sexual reproduction. The benefits of apomixis is mainly seen in the absence of pollinating agents and extreme environmental conditions.
Examples of plants showing apomixis include meadow grasses, blackberries, shadbush, dandelions, etc. The method of apomixis where development of organisms takes place without fertilization is called parthenogenesis. Unlike apomixis, it is very common in lower plants and invertebrates.
What is Apomixis?
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Apomixis is the mode of reproduction in which seed formation in plants occurs without fertilization. In higher plants, this type of reproduction is very common. The following are some important concepts that lay the foundation of apomixis. The term ‘apomixis’ was coined by the famous botanist Hans Winker.
- During sexual reproduction, fertilization occurs due to the fusion of male and female gamete to form a zygote.
- Apomixis is an asexual form of reproduction that does not include the formation of gamete and zygote.
- This process never leads to genetic recombination and variability in population.
- The offspring produced by apomixis shows gene flow.
- Hence, the rapid development of pure lines can be achieved by a single set of chromosomes.
- Plants of more than 35 families are known to be apomictic.
- Gramineae, Compositae, Rutaceae, and Rosaceae are some examples of plant family showing apomixis.
Types of Apomixis
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Based on Cell Involved
Based on the cells involved this apomixis can be further classified as parthenogenesis, diplospory, apospory, and adventitious embryony. Parthenogenesis is where embryo develops from an egg cell.
1. Diplospory Apomixis
Diplospory occurs either by mitotic division or by interrupting meiosis. In this type of apomixis, eight-nuclei cell structure is formed by three continous mitotic cell divisions. Examples of diplospory apomixis are Taraxacum, Ixeris, and Antennaria.
2. Apospory Apomixis
Apospory apomixis involves the development of an apomictic embryo sac by nuclear cells. The most common type of apomixis observed in higher plants is apospory apomixis. The timing of initiation of apospory apomixis in the plant may coincide with or overlap with embryo sac formation.
3. Adventitious Embryony
The direct development of an embryo from the nucellus is called aventitious embryony. It is a type of saprophytic reproduction observed in Garcinia, Mangifera indica, etc. A bud-like structure is formed during the process of adventitious embryony.
Based on Occurrence
On the basis of occurrence, it is classified into recurrent apomixis and non-recurrent apomixis.
1. Recurrent Apomixis
Recurrent apomixis also known as gametophytic apomixis is a process where diploid egg cell and embryonic cell is developed from the megaspore mother cell.
2. Non-recurrent Apomixis
In non-recurrent apomixis, both the egg cell and embryo are haploid and the embryo is developed directly from an egg cell without fertilization.
Based on Frequency
Frequency involves the following two types of apomixis:
1. Obligate Apomixis
In Obligate apomixis, reproduction takes place by apomictic means.
2. Facultative Apomixis
In Facultative apomixis, the process of reproduction is carried out by both apomictic and sexual means. Sorbus, brambles, hawthorns, shadbush, and blackberries, hawkweeds, meadow grasses, mat grass, etc. are few examples where apomixis takes place.
Applications of Apomixis
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The apomixis has application in the production sector. Some of important applications of apomixis are mentioned as follows :
Maintaining Purity
In case of obligate apomixis, the characteristics of the mother plant are retained. This helps to carry the same genotype through several generations.
Conservation of Heterosis
The improved characteristics, functions, and yield of a hybrid organism is called heterosis. There is no segregation in apomixis, hence heterosis is conserved easily. Also, obligate recurrent apomixis conserves hybrid vigor.
Pure lines Development
Haploid plants are produced through haploid apogamy and parthenogenesis. These plants, after being treated with colchicine produce pure lines and help in getting higher yields.
Hybrid Seed Production
Apomixis makes hybrid seed production a very easy process. Without any crossing, seeds are produced automatically through apomictic means. After the development of a hybrid, the hybrid seed production occurs automatically.
Advantages of Apomixis
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The following are the advantages of Apomixis:
- It helps in maintaining uniformity in generations for both homozygotes and heterozygotes.
- Reproduction is guaranteed even in the absence of pollinators.
- Genetically uniform progenies can be produced rapidly without segregation.
- An increase in reproduction efficiency can be found.
- Permanent fixation of hybrid vigor takes place in crop plants.
- It also affects the efficient exploitation of the maternal characteristics in the resulting progenies.
Significance of Apomixis
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Apomixis in plant breeding has a huge significance as this method helps in developing seeds without fertilization. The hybrid seeds produced by this method are cost-efficient and also give large scale production in less time.
- Apomixis does not involve cross-fertilization, so it helps to retain the good characteristics of the crop plants.
- Production of hybrid seeds takes place without the need of cross-breeding.
- This helps in increasing the yield and productivity of crops.
Things to Remember
- Apomixis is a process of formation of seeds without gamete formation.
- Based on the cells involved, frequency, and occurrence, classification of apomixis is done.
- It plays a significant role in maintaining uniformity in both homozygotes and heterozygotes.
- A group of similar individuals that produce organisms of the same phenotype are called pure lines.
- Maize and wheat are examples of crop plants that shows the process of apomixis.
Previous Years Questions
- Meiosis takes place in...[NEET 2013]
- The sexual reproduction is absent in….[NEET 1995]
- Attractants and rewards are required for….[NEET 2017]
- Functional megaspore in an angiosperm develops into ?...[NEET 2017]
- Coconut water from a tender coconut is….[NEET 2015]
- Double fertilization is exhibited by….[NEET 2017]
- Pollen tablets are available in the market for...[NEET 2014]
- Geitonogamy involves….[NEET 2014]
- Which one of the following fruits is parthenocarpic?...[NEET 2015]
- Seeds without fertilization is obtained from...[KCET 2015]
- Identify the vegetative propagule M in the...[KCET 2020]
- The process in which haploid embryo is formed from haploid egg without fertilization is called...[KEAM]
- Gemmules are internal buds found in sponges and are….
- Residual, persistent nucellus present in some seeds is known as...[AMUEEE 2014]
- A typical dicotyledonous embryo consists of….[AMUEEE 2010]
- Body of ovule is attached to funicle at a point called...[AMUEEE 2013]
- Chalazogamy is shown by...[AMUEEE 2015]
- Cleistogamous flower is found in...[JKCET 2011]
Sample Questions
Ques. What are some of the salient features of recurrent and non-recurrent apomixis? (3 marks)
Ans. In Recurrent apomixis, the diploid cells develop an embryo-sac without disturbing the chromosome number. All the plants produced by this type of apomixis have 2n number of chromosomes and are very fertile.
- In Non-recurrent apomixis, the haploid cells develop the embryo-sac.
- All the plants produced by this type of apomixis are haploid and sterile.
- This is widely used for developing inbred lines and also includes haploid apogamy and haploid parthenogenesis.
Ques. What are the limitations of apomixis? (2 marks)
Ans. Ineffective selection : Due to the lack of heritable variation, the plants have the same genotype, that is either homozygous or heterozygous.
- Frequency is low : The apomictic lines are found in very few crop plants with low frequency. However, frequency is more in case of fruit crops.
- Genetic diversity : Low genetic diversity is found in obligate apomictic lines. However, apomictic lines are highly uniform genetically.
- Lack of gene flow : Due to the occurence of recombinations in apomictic populations, there is a lack of gene flow.
Ques. What are the benefits of apomixis? (1 mark)
Ans. Apomixis produces new generations of plants which are very identical to the parent plants. This is very cost efficient as well as time efficient in faster production of feed and fiber around the world. This preserves good character over generations and also allows the introduction of other desirable characters.
Ques. What is the meaning of word apomixis? (1 mark)
Ans. Apomixis is the Greek word means away from mixing. ‘Apo’ means away from and ‘mixi’ means mixing.
Ques. What is obligative and Facultative apomixis? (2 marks)
Ans. Obligative and facultative apomixis comes under the class frequency.
- Obligative apomixis is the reproduction mode where offspring is developed by apomictic means.
- Facultative apomixis is the process of reproduction that carried out by both apomictic and sexual means.
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