Question Bank [2022] — BIOLOGY STD 12 Science — Question

i. Recurrent apomixis:

1. In this type, the embryo sac generally rises either from an archesporial cell or from some other part of the nucellus.
2. In diplospory, the unreduced embryo sac is derived from the diploid megaspore mother cell e.g. Taraxacum.
3. In apospory, the nucellar cells give rise to the apomictic embryo sac.

ii. Non-recurrent apomixis:

1. In this type, the megaspore mother cell undergoes usual meiotic division and a haploid embryo sac is formed.
2. Here, the embryo arises either from the egg by parthenogenesis or from some other haploid cells of gametophyte through apogamy.
3. Plants produced by this method are generally sterile and do not reproduce sexually, e.g. Nicotiana.

iii. Adventive Embryony:

1. In this type, embryos may develop from somatic nucellus or integuments along with normal zygotic embryo.
2. It is common in Mango, Orange, Lemon, etc. It gives rise to a condition called polyembryony.