If the haploid number for a plant species is 4, how many chromosomes are found in a member of the species that has one of the following characteristics? Explain your reasoning in each case.
Trisomy

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Understand the concept of haploid number: The haploid number (n) represents the number of chromosomes in a single set of a species' genome. For this plant species, the haploid number is given as 4, meaning n = 4.

Determine the diploid number: In diploid organisms, the total number of chromosomes is twice the haploid number. Therefore, the diploid number (2n) for this species is 2 × 4 = 8 chromosomes.

Understand trisomy: Trisomy refers to the presence of an extra chromosome in addition to the normal diploid set. This means that instead of having two copies of a particular chromosome, the organism has three copies of that chromosome.

Calculate the total number of chromosomes in a trisomic individual: Since the diploid number is 8, adding one extra chromosome for trisomy results in 8 + 1 = 9 chromosomes.

Explain the reasoning: The extra chromosome in trisomy arises due to nondisjunction during meiosis, where chromosomes fail to separate properly. This leads to an individual having one additional chromosome beyond the normal diploid set.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Haploid and Diploid Numbers

The haploid number (n) refers to the number of chromosomes in a gamete, which is half the total number of chromosomes in a diploid organism. In this case, if the haploid number for the plant species is 4, the diploid number (2n) would be 8, representing the total chromosomes in somatic cells.

Trisomy

Trisomy is a genetic condition where an individual has three copies of a particular chromosome instead of the usual two. This results in a total of one extra chromosome, leading to a total chromosome count of 2n + 1. For the plant species in question, this would mean having 9 chromosomes (8 diploid + 1 extra).

Chromosome Number Calculation

To determine the chromosome number in a specific genetic condition, one must understand how to calculate the total based on the haploid and diploid numbers. For a plant with a haploid number of 4, the diploid number is 8, and in the case of trisomy, the total chromosome count becomes 9, which is essential for understanding genetic variations in this species.

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