Apomixis

1) Apomixis 

It is the process in which embryos are formed through asexual method of reproduction without formation of gametes and the act of fertilization. 

2) Apogamy- when a gametophyte organ or cell produces embryo like structure without fertilization, it is termed apogamy. 

3) Apospory- when diploid sporophyte cell produces a diploid gametophyte without undergoing meiosis is called apospory. 

Categories of apomixis: 

1. Recurrent apomixis- This type of embryo sac typically arises from an archesporial cell or another component of the nucellus. Diplospory occurs when a diploid megaspore, such as Taraxacum, produces an unreduced embryo sac. Apospory occurs when nucellar cells form apomictic embryo sacs. 

2. Non-recurrent apomixis- The megaspore mother cell divides normally, resulting in a haploid embryo sac. The embryo can develop from the egg through parthenogenesis or from other haploid gametophyte cells through apogamy. This approach produces sterile, non-sexually reproducing plants, such as Nicotiana. 

3. Adventive Embryony- In this type, embryos may develop from somatic nucellus or integuments alongside regular zygotic embryos. It is commonly found in fruits such as mango, orange, and lemon. It causes polyembryony.