What you think of as 'a banana' is a Cavendish, one variety of the species Musa acuminate. It is a triploid organism (3n) with three sets of chromosomes in every somatic cell. The Cavendish cannot be naturally bred; it can only be reproduced by cloning. Explain how its triploid state accounts for its inability to form normal gametes. Discuss how the lack of sexual reproduction might make the species particularly vulnerable to a new pest.

Verified step by step guidance

1. Understand the concept of ploidy: A triploid organism (3n) has three sets of chromosomes in each somatic cell. This is different from diploid organisms (2n), which have two sets of chromosomes, one from each parent. In sexual reproduction, gametes are formed through meiosis, which requires homologous chromosomes to pair and segregate evenly.
2. Explain why triploidy disrupts meiosis: During meiosis in a triploid organism, homologous chromosomes cannot pair evenly because there are three copies of each chromosome instead of two. This leads to uneven segregation of chromosomes, resulting in gametes with an abnormal number of chromosomes (aneuploidy). Such gametes are typically nonviable or result in nonfunctional offspring.
3. Connect this to the Cavendish banana: Since the Cavendish banana is triploid, it cannot produce viable gametes through meiosis. This is why it cannot reproduce sexually and must rely on cloning (asexual reproduction) for propagation. Cloning involves producing genetically identical offspring from a parent plant, bypassing the need for gametes.
4. Discuss the vulnerability due to lack of genetic diversity: Sexual reproduction introduces genetic variation through processes like crossing over and independent assortment during meiosis. This variation helps populations adapt to environmental changes, such as new pests or diseases. In contrast, cloning produces genetically identical individuals, meaning the entire population has the same genetic makeup.
5. Explain the risk of pest vulnerability: If a new pest or disease arises that can exploit the genetic weaknesses of the Cavendish banana, the entire population is at risk because there is no genetic diversity to provide resistance. This makes the species particularly vulnerable to extinction from such threats.

Key Concepts

Triploidy

Triploidy refers to a condition where an organism has three complete sets of chromosomes (3n) instead of the usual two (2n). In the case of the Cavendish banana, this triploid state disrupts normal meiosis, the process that produces gametes, leading to the formation of non-functional gametes. As a result, triploid organisms like the Cavendish cannot undergo sexual reproduction, which relies on the production of viable sperm and egg cells.

Clonal Reproduction

Clonal reproduction is a form of asexual reproduction where an organism produces genetically identical offspring without the need for gametes. In the case of the Cavendish banana, this means that all plants are clones of the original, leading to a lack of genetic diversity. While this allows for uniformity and consistency in desirable traits, it also means that the entire population is susceptible to the same diseases and pests, as there is little to no variation in their genetic makeup.

Vulnerability to Pests

The lack of sexual reproduction and genetic diversity in the Cavendish banana makes it particularly vulnerable to new pests and diseases. When a new pest arrives, it can potentially affect all individuals in the population since they share the same genetic traits. This uniformity means that if a pest evolves to overcome the plant's defenses, it can devastate the entire crop, leading to significant agricultural and economic consequences.