Seed, Apomixis & Polyembryony - NEET MCQ

Apomixis in flowering plants is defined as the asexual formation of a seed from the maternal tissues of the ovule, avoiding the processes of meiosis and fertilization, leading to embryo development.
Apomixis relates to mechanisms where an embryo sac is mitotically formed from a diploid cell in the ovule, bypassing meiosis. The genetic nature of plants produced by apomictic embryos is the same as that of parents so they can be called clones. Hence, the mother cell is diploid, so diploid embryo forms.
So, the correct answer is 'Without fertilisation diploid embryo forms'.

Apomixis (apo-without, mixis-fusion) is a mode of reproduction in some plants which results in the formation of seeds without gametic fusion. It is a form of asexual reproduction. In plants apomixis commonly mimics sexual reproduction but produces seeds without fertilisation, e.g., some species of Asteraceae and grasses. There are several methods of apomictic development in seeds.

The occurrence of multiple embryos in a seed is known as polyembryony. Polyembryony can be divided into two types:
1. True polyembryony: In this type, more than one embryos are formed within a single embryo sac. The extra embryos may arise from the cleavage of egg or zygote, from the synergids or antipodal cells or from the endosperm as all of these lies inside the embryo sac. When the extra embryos develop from the tissues outside the embryo sac, such as nucellus it is called adventitive polyembryony.
2. False polyembryony: When two or more embryos develop from different embryo sacs, it is called false polyembryony. The extra embryos may develop from another megaspore derived from megaspore mother cell or from a different megaspore mother cell. Polyembryony can be gametophytic and sporophytic also. When the extra embryos arise from gametophytic cells of the ovule, it is called gametophytic polyembryony and when they are derived from zygote or proembryo or from initial sporophytic cells of the embryo, it is called sporophytic polyembryony.
Thus, the correct answer is option B.

Polyembryony refers to the presence of more than one embryos in a seed. It may be due to the presence of more than one egg cell in an embryo sac or more than one embryo sac in the ovule or all the egg cell may get fertilized. In Nymphaea, cleavage or splitting of embryo into two or more embryos occurs leading to the formation of multiple embryos. Such polyembryony is known as cleavage polyembryony.
Adventitive polyembryony occurs in Citrus, Mangifera and Opuntia in which diploid nucellar and integument cells proliferate to form embryos. When the endosperm develops into an additional embryo, it is known as endosperm polyembryony.
Thus, the correct answer is option A.

The progeny produced by the vegetative reproduction and apomixis are identical to their parents as the process of fusion of gametes do not take place so there is no recombination of characters. The offsprings are produced by mitosis.
Apomixis is a mode of asexual reproduction. The development of plants takes place without fusion of gametes. It is a powerful tool which fixes heterosis. The developed seeds are maternal clones. The somatic cell directly forms aposporous initial cells which forms embryo and finally develops into seed. In some cases, the megaspore mother cell directly forms the embryo sac and develops into the seed.
Vegetative propagation is the method of propagation of plant by vegetative parts of the plant.
So, the correct answer is option D.

Polyembryony is the occurrence of more than one embryo in a single seed. In adventive polyembryony, there is the formation of extra embryos due to sporophytic budding. One or more sporophytic cells, either nucellus or integuments undergo stages of embryogeny and eventually develop into mature embryos. This kind of polyembryony is found in citrus fruits. So, the correct answer is D.

Polyembryony is the phenomenon of occurrence of two or more embryos in one ovule. When the embryos arise in the same embryo sac it uis known as true polyembryony. When extra embryos develop in one embryo sac other than the zygotic embryo sac, it is known as false polyembryony.
When the embryos are formed from cells of nucellus which penetrate into the embryo sac, it is known as adventitious polyembryony such as in mango. Sometimes when one of the embryo develops from synergid, which is haploid tissue and other from nucellus which is diploid, then it is known as haploid-diploid polyembryony such as in flax.
Thus, the correct answer is option A.

The phenomenon of development of more than one embryos in a seed is known as polyembryony. It may be classified into true and false polyembryony. In true polyembryony, the embryos arise in the same embryo sac in which zygotic embryo has developed while in false polyembryony, extra embryos develop in another embryo sac.
Thus, the correct answer is option C.