Question
Write a short note on Apomixis and polyembryony.
✓
Answer
→ Seeds in general are the products of fertilisation, but in a few flowering plants such as some species of Asteraceae and grasses a special mechanism, to produce seeds without fertilisation, called apomixis have evolved.
→ Thus, apomixis is a form of asexual reproduction that mimics sexual reproduction.
→ Types: There are several ways of development of apomictic seeds.
(i) Recurrent agamospermy:
→ In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilisation.
(ii) Adventive embryony:
→ More often, as in many citrus and mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos.
→ In such species each ovule contains many embryos. Occurrence of more than one embryo in a seed is referred to as polyembryony.
→ Thus, apomixis is a form of asexual reproduction that mimics sexual reproduction.
→ Types: There are several ways of development of apomictic seeds.
(i) Recurrent agamospermy:
→ In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilisation.
(ii) Adventive embryony:
→ More often, as in many citrus and mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos.
→ In such species each ovule contains many embryos. Occurrence of more than one embryo in a seed is referred to as polyembryony.
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