Question

For a species with a diploid number of \(18,\) indicate how many chromosomes will be present in the somatic nuclei of individuals that are haploid, triploid, tetraploid, trisomic, and monosomic.

Short answer

Answer: The number of chromosomes in the somatic nuclei of individuals are as follows: - Haploid: 9 - Triploid: 27 - Tetraploid: 36 - Trisomic: 19 - Monosomic: 17

Step-by-step solution

Haploid

A haploid (n) refers to a cell or an organism with a single set of chromosomes.

Diploid

A diploid (2n) refers to a cell or an organism with two sets of chromosomes, one from each parent.

Triploid

A triploid (3n) refers to a cell or an organism with three sets of chromosomes.

Tetraploid

A tetraploid (4n) refers to a cell or an organism with four sets of chromosomes.

Trisomic

A trisomic refers to a cell or an organism carrying an extra chromosome (2n + 1).

Monosomic

A monosomic refers to a cell or an organism carrying one fewer chromosome (2n - 1). **Step 2: Calculating the number of chromosomes for each term based on the given diploid number 18**

Haploid individual (n)

For a haploid individual, the number of chromosomes is equal to a single set of chromosomes. Since the diploid number is 18 (2n = 18), a haploid individual will have n = 18/2 = 9 chromosomes.

Triploid individual (3n)

For a triploid individual, the number of chromosomes is equal to three sets of chromosomes. Since the haploid number is 9, a triploid individual will have 3n = 3 * 9 = 27 chromosomes.

Tetraploid individual (4n)

For a tetraploid individual, the number of chromosomes is equal to four sets of chromosomes. Since the haploid number is 9, a tetraploid individual will have 4n = 4 * 9 = 36 chromosomes.

Trisomic individual (2n + 1)

For a trisomic individual, the number of chromosomes is equal to the diploid number plus an extra chromosome. Since the diploid number is 18, a trisomic individual will have 2n + 1 = 18 + 1 = 19 chromosomes.

Monosomic individual (2n - 1)

For a monosomic individual, the number of chromosomes is equal to the diploid number minus one chromosome. Since the diploid number is 18, a monosomic individual will have 2n - 1 = 18 - 1 = 17 chromosomes. In conclusion, the number of chromosomes present in the somatic nuclei of individuals that are haploid, triploid, tetraploid, trisomic, and monosomic are 9, 27, 36, 19, and 17, respectively.

Key concepts

Haploid

A haploid cell or organism has just one complete set of chromosomes. This number is denoted as "n". In sexually reproducing organisms, gametes (sperm and egg cells) are haploid, ensuring that when they combine during fertilization, the diploid state is restored.
For instance, in the given exercise, we see that when a species has a diploid number of 18, this means its full set of chromosomes is 18. Thus, each gamete or haploid cell of this species carries half of that number:

• So, in this example, the haploid number (n) would be 9.

Haploid cells are crucial for genetic diversity, which arises from processes like meiosis, where genetic material is shuffled and halved to create unique gametes.

Diploid

A diploid organism contains two complete sets of chromosomes, one from each parent, making it 2n. This is the standard state for most cells in an organism, such as human somatic cells. These chromosome pairs are homologous, meaning they carry the same types of genes, though not necessarily identical versions.
Using the species example where the diploid number is 18, a diploid cell has two sets of 9 chromosomes:

• Thus, the diploid number for this organism is 18 chromosomes total.

This diploid configuration ensures that any changes or damages in one chromosome can potentially be corrected or compensated by its homologous partner, thereby contributing to stability in genetic information.

Polyploidy

Polyploidy describes a condition where an organism has more than two complete sets of chromosomes. There are different forms based on how many sets there are, such as triploid (3n) or tetraploid (4n). This happens more often in plants, where it can result in species with enhanced growth or new varieties.

• For example, triploids would have 27 chromosomes (3 sets of 9), like in the example given of triploid individuals.
• Tetraploids, on the other hand, would have 36 chromosomes.

Polyploidy can lead to larger cell size and, in plants, might result in more robust characteristics. However, polyploidy in animals, especially vertebrates, is typically less common and can be problematic.

Trisomic

Trisomic refers to individuals having an extra chromosome, resulting in a total of 2n + 1 chromosomes. In humans, this situation is responsible for specific disorders depending on which chromosome is triplicated. A well-known example in humans is Down syndrome, which involves an extra copy of chromosome 21.
For the exercise at hand, where the species' diploid number is 18, a trisomic organism would have:

• 19 chromosomes in total (18 + 1).

The presence of an extra chromosome can disrupt normal development and function, as seen in genetic conditions where normal gene balance is upset by the additional chromosome.

Monosomic

Monosomic individuals carry one fewer chromosome than the normal diploid number, denoted as 2n - 1. This situation results from nondisjunction during meiosis, where chromosomes fail to separate correctly.
This condition can lead to various developmental issues because the individual lacks one copy of a set of genes.

• For example, with the species given a diploid number of 18, a monosomic individual would contain 17 chromosomes.

Monosomy can be detrimental depending on which chromosome is missing, as the organism may lack essential genetic information that its development or survival depends on.