Difference Between Apomixis and Polyembryony

What Is Apomixis?

Apomixis is defined as the asexual method of production of seeds or embryos without fertilization. In this process, the embryo develops from a somatic cell or an unreduced female gametophyte, resulting in genetically identical offspring.

Characteristics Of Apomixis

Apomixis is a special type of asexual reproduction in plants where seeds are formed without fertilisation. This process has some unique features that make it useful for farming and crop improvement, as given below:

• Asexual Reproduction: Apomixis allows for the production of seeds without the involvement of gametes or fertilization.

• Genetic Uniformity: Offspring produced through apomixis are genetically identical to the maternal plant.

• Bypassing stages of meiosis: In some forms of apomixis, the embryo develops from a cell that has not undergone meiosis, maintaining the diploid chromosome number.

• Potential for Crop Improvement: Apomixis has potential applications in agriculture for the production of hybrid crops and the preservation of desirable traits.

What Is Polyembryony?

Polyembryony is the development of two or more embryos within a single seed or ovule. This process can occur through various mechanisms, including the cell division of the zygote, the development of embryos from nucellar tissue, or the formation of adventitious embryos from other parts of the ovule.

Characteristics Of Polyembryony

Polyembryony is a process where more than one embryo forms in a single seed.This process has some unique features that make it useful for farming and crop improvement, as given below:

1. Multiple Embryos: A single seed or ovule produces two or more embryos, resulting in the formation of genetically distinct individuals.

2. Genetic Variation: Polyembryony can lead to genetic variation among the resulting embryos, depending on the origin of the additional embryos.

3. Asexual Reproduction: In some cases, polyembryony can be considered a form of asexual reproduction, as it allows for the production of genetically identical offspring without the involvement of gametes.

4. Importance in Agriculture: Polyembryony has applications in agriculture, particularly in the production of clonal planting materials and the development of new cultivars.

Key Differences Between Apomixis And Polyembryony

Apomixis and polyembryony are two distinct phenomena in plants that involve the production of multiple embryos without the fusion of gametes. Understanding the differences between apomixis and polyembryony provides insights into the diversity of reproductive strategies in plants and their potential applications in agriculture and horticulture.

MCQs in Apomixis And Polyembryony

Question 1: The Following are certain statements regarding apomixis in plants:

P. Apomixis cannot be used to maintain hybrid vigor over many generations in plants.

Q. In sporophytic apomixis maternal genotype is maintained.

R. There is an event of meiosis during gametophytic apomixis, which is also referred to as apomeiosis.

S. In diplospory, meiosis of the megaspore mother cell is aborted, resulting in two unreduced spores, out of which one forms the female gametophyte.

Which one of the following combinations is correct?

1. P and Q

2. P and R

3. Q and R

4. Q and R

Answer: Q. In sporophytic apomixis maternal genotype is maintained.

S. In diplospory, meiosis of the megaspore mother cell is aborted, resulting in two unreduced spores, out of which one forms the female gametophyte.

Statement P is incorrect. Apomixis, which involves asexual reproduction, cannot maintain hybrid vigour over many generations since it does not involve the recombination and genetic variation that occur through sexual reproduction.

Statement R is incorrect. Meiosis is not a part of gametophytic apomixis, and it is not referred to as apomeiosis. Gametophytic apomixis involves the development of an embryo from an unreduced egg cell or a modified female gametophyte without the need for fertilization.

Therefore, the correct combination is Q and S. In sporophytic apomixis, the maternal genotype is maintained, and in diplospory, meiosis of the megaspore mother cell is aborted, resulting in two unreduced spores, one of which forms the female gametophyte.

Hence, the correct answer is option 4) Q and S.

Question 2: What is common between vegetative reproduction and apomixis.

1. Both are applicable only to dicot plants.

2. Both bypass the flowering phase

3. Both occur throughout the year

4. Both produce progeny identical to the parent

Answer: Both vegetative reproduction and apomixis produce progeny that are genetically identical to the parent, referred to as clones. These forms of asexual reproduction do not involve the formation of gametes or fertilization and rely on a single parent for reproduction. In vegetative reproduction, new plants arise from vegetative parts like roots, stems, or leaves, while in apomixis, seeds are formed without fertilization, bypassing the typical sexual reproduction process. Both methods ensure the preservation of genetic uniformity across generations.

Hence, the correct answer is option 4) Both produce progeny identical to the parent.

Question 3: Which of the following is true about polyembryony?

1. It is a type of asexual reproduction in plants.

2. It results in the formation of genetically identical offspring.

3. It involves the development of seeds without fertilization.

4. A single fertilized egg gives rise to multiple embryos in polyembryony.

Answer: Polyembryony is a phenomenon where a single fertilized egg gives rise to multiple embryos in polyembryony. It is a type of reproductive strategy found in some plants, where the fertilized egg divides multiple times to form multiple embryos, resulting in the development of multiple seedlings from a single seed. Hence option D is the correct answer.

Option(A) Polyembryony is a type of sexual reproduction. Hence option A is incorrect.

Option(B) Polyembryony results in the formation of genetically identical offspring but they are distinct from their parents. Hence option B is incorrect.

Option(C) Apomixis involves the development of seeds without fertilization. Hence option C is incorrect.

Hence, the correct option is 4) A single fertilized egg gives rise to multiple embryos in polyembryony.