Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Apomixis is a form of asexual reproduction that mimics sexual reproduction, where seeds are produced without the process of fertilization.
In some species, a diploid () egg cell is formed without reduction division (meiosis) and develops into an embryo without fertilization.
Polyembryony refers to the occurrence of more than one embryo in a single seed. This is frequently observed in genera such as and .
Adventive polyembryony occurs when diploid cells of the nucellus or integuments surrounding the embryo sac start dividing, protrude into the embryo sac, and develop into multiple embryos.
Hybrid seeds produced via apomixis are highly beneficial in agriculture because they prevent the segregation of traits in progeny, allowing farmers to reuse seeds for several years without losing hybrid vigor.
The ploidy of embryos derived from nucellar cells in apomictic seeds is always diploid (), as they are genetically identical to the maternal parent.
📐Formulae
💡Examples
Problem 1:
In a case of polyembryony, if the mother plant is diploid (), what will be the chromosome number in the cells of the nucellar embryos?
Solution:
Explanation:
Nucellar embryos develop from the diploid () cells of the nucellus through mitosis without undergoing meiosis or fertilization. Therefore, the chromosome number remains the same as the maternal tissue, which is .
Problem 2:
Why are apomictic seeds preferred over hybrid seeds produced through normal sexual reproduction for commercial farming?
Solution:
To prevent segregation of characters.
Explanation:
Hybrid seeds produced by sexual reproduction undergo meiosis and syngamy, leading to the segregation of traits in the next generation. If these hybrids are made into apomicts, the embryos are clones of the parent, ensuring the desirable hybrid characters are maintained in the progeny (, etc.) without the need to buy expensive new seeds every year.