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Questions and Answers
What is formed from the megagametophyte following three mitotic divisions?
What is formed from the megagametophyte following three mitotic divisions?
Which type of apomixis involves the embryo developing directly from the egg-cell without fertilization?
Which type of apomixis involves the embryo developing directly from the egg-cell without fertilization?
In obligate apomixis, what happens to the characteristics of the mother plant?
In obligate apomixis, what happens to the characteristics of the mother plant?
Which of the following statements is true regarding apo- embryony?
Which of the following statements is true regarding apo- embryony?
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What is the outcome of apogamy apomixis?
What is the outcome of apogamy apomixis?
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What distinguishes facultative apomixis from obligate apomixis?
What distinguishes facultative apomixis from obligate apomixis?
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Which of the following is a characteristic of recurrent apomixis?
Which of the following is a characteristic of recurrent apomixis?
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What role does apomixis have in the conservation of hybrid vigor?
What role does apomixis have in the conservation of hybrid vigor?
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What is Apomixis?
What is Apomixis?
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Which of the following is a type of apomixis based on cell involved?
Which of the following is a type of apomixis based on cell involved?
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What is the primary characteristic of sporophytic apomixis?
What is the primary characteristic of sporophytic apomixis?
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Who is credited with the first discovery of apomixis?
Who is credited with the first discovery of apomixis?
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What is the primary advantage of apomixis in seed production?
What is the primary advantage of apomixis in seed production?
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Which of the following describes the genetic outcomes of apomixis?
Which of the following describes the genetic outcomes of apomixis?
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How does apomixis contribute to crop yield?
How does apomixis contribute to crop yield?
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Which classification method is NOT used for apomixis?
Which classification method is NOT used for apomixis?
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What limitation is associated with apomictic plants?
What limitation is associated with apomictic plants?
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What occurs in gametophytic apomixis?
What occurs in gametophytic apomixis?
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In which of the following plants is diplospory apomixis commonly observed?
In which of the following plants is diplospory apomixis commonly observed?
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What happens to the genetic structure of apomictic plants over generations?
What happens to the genetic structure of apomictic plants over generations?
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Which of the following is NOT a benefit of apomixis?
Which of the following is NOT a benefit of apomixis?
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What is the effect of apomixis on hereditary variation?
What is the effect of apomixis on hereditary variation?
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In which type of crops is the frequency of apomictic lines generally higher?
In which type of crops is the frequency of apomictic lines generally higher?
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What characteristics of progenies can apomixis help to exploit?
What characteristics of progenies can apomixis help to exploit?
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Study Notes
Apomixis Overview
- Apomixis is a type of reproduction where seeds form without the union of gametes.
- It's derived from the Greek words "apo" (away from) and "mixis" (mixing/mingling).
- Sexual organs participate, but fertilization doesn't occur.
- It results in clonal seed production.
- The genotype of the offspring is identical to the parent plant.
Apomixis Discovery
- The first discovery of apomixis was in citrus seeds.
- Leuwen Ock identified it in 1719.
Mechanisms of Apomixis
Apospory
- Embryo sac originates from a diploid cell (not the megaspore mother cell) via mitosis.
- This can occur directly or after interrupted meiosis.
- A key difference from traditional seed development.
Androgenesis
- Embryo sac originates from the generative nucleus in pollen.
- The most common apomixis mechanism in higher plants.
- Multiple embryo sacs are often present.
Gametophytic Apomixis
- Unfertilized cells develop into a megagametophyte.
- Critical for the generation process.
Sporophytic Apomixis
- Unfertilized cells directly develop into an embryo.
- A significant apomixis form.
Haploid Parthenogenesis
- Embryo forms from an unfertilized egg cell.
- A common characteristic of apomixis.
Haploid Apogamy (Pseudogamy)
- Embryo arises from synergids or antipodal cells.
- A critical aspect of apomixis mechanisms.
Adventitious Embryony
- Embryo develops directly from nucellus or integuments.
- No embryo sac is formed.
- Common in mango and citrus.
Types of Apomixis
- Recurrent Apomixis (Gametophytic): Both egg cell and embryo are diploid
- Non-Recurrent Apomixis: Egg cell and embryo are haploid, developing without fertilization,
Apomixis Occurrence
- Obligate Apomixis: Reproduction solely through apomictic means
- Facultative Apomixis: Reproduction via both apomictic and sexual means
Apomixis Frequency
- Apomixis occurs in many plant families, exceeding 35 families, with examples including sorbus, brambles, hawthorns, shadbush, and blackberries, hawkweeds, and meadow grasses, and others. Some are frequent in fruit crops,
Significance of Apomixis
- Important for plant breeding due to seed development without fertilization.
- Cost-effective and efficient for large-scale hybrid seed production and increasing yields.
- Retains desirable parental traits, and avoids cross-fertilization.
Applications of Apomixis
- Maintaining Purity: Preserving characteristics of the parent plant over multiple generations
- Conserving Heterosis: Maintaining favorable hybrid traits (hybrid vigor).
- Pure Line Development: Produces uniform, genetically stable lines, leading to higher yields.
- Hybrid Seed Production: Facilitates a streamlined process for developing hybrid seeds easily without crossing
Advantages of Apomixis
- Preserving Heterozygosity: Maintaining favorable gene combinations.
- Rapid Production of Uniform Progenies: Generating genetically uniform offspring without segregation.
- Maternal Traits Exploitation: Efficient preservation of the mother plant's characteristics
- Cost efficient in seed production for hybrid varieties.
Limitations of Apomixis
- Lack of Heritable Variation: Limited genetic variation in offspring, making it challenging to select new desirable traits,.
- Low Frequency in Some Crops: Apomixis is not common in all crops.
- Low Genetic Diversity: Reduced genetic diversity in obligate apomictic lines.
- Lack of Gene Flow: The inability of genes to freely move into the apomictic line.
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