Bananas taste soft, waxy, fragrant and sweet, and are deeply loved by people. In Africa and Southeast Asia, people in some places take bananas as their staple food and eat them after cooking or drying. When many people eat bananas, they wonder why this fruit has no seeds? How do these seedless bananas breed?
Banana originated in Asia, Malaysia and southwest China. It is one of the oldest cultivated fruit trees in the world. The current banana cultivated species originated from the wild pointed leaf banana and long stem banana. The chromosomes of the two wild banana varieties have two groups, both of which are diploid, abbreviated as 2n, and are composed of 22 chromosomes. They can produce seeds, have sexual reproduction and grow normally. However, pointed leaf banana has small fruit and good flavor, but its ability to resist harsh environment is poor, so it is not easy to plant; The long stem banana has strong adaptability, but the taste is not good. Therefore, these two wild banana varieties are not suitable for cultivation.
The chromosome composition of banana is called AA genome, and that of banana is called BB genome. Most of the banana varieties cultivated now are transformed pointed leaf banana. Their chromosome composition is AAA and they are triploid. This is the use of wild sharp leaf banana. Chromosome meiosis occurs during reproduction
Abnormal, diploid gametes are formed, and the chromosome composition is AA. Combining these gametes with haploid gametes with normal chromosome group A will produce triploid banana varieties with chromosome group AAA. This kind of banana has large fruit, good taste and high yield. It is the main cultivated banana species in modern times.
The change of chromosome composition has greatly changed the reproductive mode of triploid banana and wild diploid banana. During the reproduction of normal diploid bananas, 22 chromosomes undergo meiosis to form female or male gametes with 11 chromosomes. The combination of male and female gametes produces diploid bananas, which have normal seeds. The cultivated bananas are mostly triploid chromosomes. When they form gametes, the triploid lines composed of 33 chromosomes undergo meiosis, and the chromosome distribution is uneven. It is difficult to form a set of active gametes containing 11 chromosomes, so they cannot produce normal seeds. Therefore, we usually see bananas without seeds. Because there are no seeds, triploid bananas can not reproduce through sexual reproduction, but only through asexual reproduction.