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.
Monosomy

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Understand the haploid number: The haploid number (n) represents the number of chromosomes in a single set of the organism's genome. For this plant species, n = 4. Therefore, the diploid number (2n), which is the total number of chromosomes in a normal somatic cell, is calculated as 2 × n = 8 chromosomes.

Define monosomy: Monosomy refers to the loss of one chromosome from the diploid set. In a diploid organism, this results in a chromosome count of 2n - 1. For this plant species, the diploid number is 8, so monosomy would result in 8 - 1 = 7 chromosomes.

Explain the reasoning: Monosomy occurs when one chromosome is missing from the normal diploid set. This can happen due to errors during cell division, such as nondisjunction, where chromosomes fail to separate properly during meiosis or mitosis.

Relate to the haploid number: Since the haploid number is 4, the diploid number is 8. Monosomy reduces the chromosome count by one, resulting in 7 chromosomes. This is consistent with the definition of monosomy as 2n - 1.

Summarize the calculation: To determine the chromosome count in a monosomic individual, subtract one chromosome from the diploid number (2n). For this species, the calculation is 8 - 1 = 7 chromosomes.

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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. Understanding these terms is crucial for determining chromosome counts in various genetic scenarios.

Monosomy

Monosomy is a type of aneuploidy where one chromosome from a pair is missing, resulting in a total of one less chromosome than the diploid number. For a plant with a diploid number of 8, monosomy would mean that one chromosome is absent, leading to a total of 7 chromosomes in that individual. This concept is essential for analyzing the genetic implications of chromosome loss.

Chromosome Structure and Function

Chromosomes are structures within cells that contain DNA and proteins, playing a critical role in heredity and gene expression. Each chromosome carries specific genes that determine traits. Understanding chromosome structure helps in grasping how changes in chromosome number, such as those seen in monosomy, can affect the organism's development and function.

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