Apomixis & Parthenocarpy | Biology Class 12 - NEET PDF Download

Apomixis

• Generally, seeds are formed as a result of fertilisation.
• In some flowering plants (for example, members of Asteraceae and grasses), seeds are produced without fertilisation.
• This special mechanism of seed formation without fertilisation is called apomixis.
• Apomixis is a form of asexual reproduction that mimics sexual reproduction because seeds are formed.

Development of Apomictic Seeds

Apomictic seeds can develop in several ways:

Diploid egg cell formation

• The egg cell is formed without reduction division (meiosis).
• The diploid egg cell develops into an embryo without fertilisation.
  

Nucellar embryony

• Seen commonly in Citrus and Mango varieties.
• Some nucellar cells surrounding the embryo sac start dividing.
• These cells protrude into the embryo sac and develop into embryos.
• As a result, each ovule contains many embryos.

Polyembryony

• The occurrence of more than one embryo in a single seed is called polyembryony.
• Polyembryony is common in plants like orange (Citrus).
• Seeds of orange contain many embryos of different sizes and shapes.

Genetic Nature of Apomictic Embryos

• Apomictic embryos are formed without fertilisation.
• They are genetically identical to the parent plant.
• Hence, apomictic embryos can be considered clones.

Importance of Apomixis in Agriculture

Hybrid varieties of many food and vegetable crops are widely cultivated.

Hybrids show high productivity, but:

• Hybrid seeds must be produced every year.
• Seeds collected from hybrids show segregation in the next generation.
• Hybrid seed production is costly for farmers.

If hybrids are made apomictic:

• There is no segregation of characters.
• Farmers can reuse seeds year after year.
• Cost of hybrid seeds is reduced.

Due to its importance, active research is being carried out to:

• Understand the genetics of apomixis
• Transfer apomictic genes into hybrid varieties