Question

The primrose, Primula kewensis, has 36 chromosomes that are similar in appearance to the chromosomes in two related species, \(P .\) floribunda \((2 n=18)\) and \(P\). verticillata \((2 n=18) .\) How could P. kewensis arise from these species? How would you describe \(P\) kewensis in genetic terms?

Short answer

Describe P. kewensis in genetic terms. Answer: Primula kewensis likely arose as an allopolyploid species, where a hybridization event between P. floribunda and P. verticillata, both having 18 chromosomes, resulted in the formation of P. kewensis, having 36 chromosomes. Each parent species contributed their entire set of chromosomes to create P. kewensis.

Step-by-step solution

Identify the chromosome numbers of the species

We are given three species and their respective chromosome numbers: - Primula kewensis: \(2n = 36\) - P. floribunda: \(2n = 18\) - P. verticillata: \(2n = 18\)

Analyze the relationship between the chromosome numbers

To determine how P. kewensis arose from P. floribunda and P. verticillata, we should investigate the relationship between their chromosome numbers. It can be observed that the number of chromosomes of P. kewensis (36) is double the number of chromosomes of P. floribunda (18) and P. verticillata (18).

Hypothesize the genetic mechanism involved

Since the P. kewensis has double the number of chromosomes of P. floribunda and P. verticillata, it suggests that P. kewensis could be an allopolyploid species. Allopolyploid species arise from a hybridization event between two different species, followed by a genome duplication, in which the chromosomes from both the parent species are combined into a new species. In this scenario, both P. floribunda and P. verticillata could have contributed their entire set of chromosomes to create P. kewensis.

Describe P. kewensis in genetic terms

P. kewensis can be described as an allopolyploid species, with a diploid chromosome number of 36, which likely arose from a hybridization event between P. floribunda and P. verticillata, where both species contributed their chromosomes to the formation of P. kewensis.

Key concepts

Hybridization

Hybridization is a fascinating process where two different species come together to produce a hybrid. In the context of plants, this usually means the crossing of two species to form a new one. In our exercise, we see how both **Primula floribunda** and **Primula verticillata**, each with 18 chromosomes, came together through this process.

During hybridization, the genetic material from the two parent species combines. This combination leads to a hybrid that possesses characteristics of both parents. The offspring might show unique traits not present in either parent, or a mix of the traits from the parent species.

Ultimately, hybridization allows for the creation of genetic diversity. It brings new adaptations to existing environments or helps a species to thrive in new conditions. In the case of **P. kewensis**, hybridization was the starting point for the development of this new plant species.

Chromosome Number

Understanding chromosome numbers is crucial in biology. Chromosomes are structures that contain DNA, which holds our genetic information. Each species has a fixed number of chromosomes, known as its diploid number, represented as **2n**. For instance, both **P. floribunda** and **P. verticillata** each have a chromosome number of 18, or 2n = 18. Meanwhile, **P. kewensis** has a total of 36 chromosomes, or 2n = 36. It's interesting to note that the chromosome number of **P. kewensis** is exactly double that of each parent species.

This doubling indicates that both species contributed their full set of chromosomes to **P. kewensis**. New species with a doubled chromosome set, such as in this case, oftentimes exhibit increased vigor or different traits from their parent plants due to having combined genetic material. This kind of doubling, seen in **P. kewensis**, illustrates a special genetic condition called allopolyploidy.

Genetic Mechanism

The genetic mechanism here primarily revolves around a remarkable phenomenon called allopolyploidy. This process involves the combination and duplication of chromosomes from two different species. In the given exercise, **P. kewensis** evolved through this mechanism. The essential steps were:

• Hybridization of **P. floribunda** and **P. verticillata**, leading to a hybrid plant.
• Followed by genome duplication, where the hybrid plant doubled its chromosomes, combining the sets from both parent species to become a stable, new species.

What makes allopolyploidy fascinating is how it stabilizes the genetic material from both parents. This ensures that the new species inherits a complete set of genes from each ancestor. Therefore, allopolyploidy not only allows for species like **P. kewensis** to exist, but it also provides them a genetic advantage, potentially giving rise to novel traits and possibly greater adaptability to their environment.