Problem 8 - Biology

Question

A particular plant species has a diploid chromosome number of 20. A haploid cell of that species at mitotic prophase contains a total of ____________ chromosomes and ____________ chromatids. (a) 20; 20 (b) 20; 40 (c) 10; 10 (d) 10; 20 (e) none of the preceding, because haploid cells cannot undergo mitosis

Step-by-Step Solution

Answer

The correct answer is (d) 10; 20.

Step 1: Understanding Haploid and Diploid Cells

A haploid cell contains half the number of chromosomes of a diploid cell. Since diploid cells of this species have 20 chromosomes, a haploid cell will have half of that number.

Step 2: Calulate Chromosome Number for Haploid Cell

Divide the diploid chromosome number by 2 to find the haploid chromosome number. In this case, it's \( \frac{20}{2} = 10 \). Thus, the haploid cell contains 10 chromosomes.

Step 3: Predict Chromatid Number during Mitotic Prophase

During mitotic prophase, each chromosome is duplicated and consists of two sister chromatids. Hence, a haploid cell with 10 chromosomes at prophase will have 10 x 2 chromatids.

Step 4: Final Calculation of Chromatids

Multiply the number of chromosomes by 2 to find the number of chromatids: \( 10 \times 2 = 20 \) chromatids in prophase of haploid mitosis.

Key Concepts

Diploid Chromosome Number

In biology, organisms can have either haploid or diploid cells based on their chromosome count. The term "diploid" signifies that the cell contains two complete sets of chromosomes, one from each parent. To illustrate, in humans, the diploid chromosome number is 46, meaning there are 23 pairs
of chromosomes equivalent to 46 chromosomes in total. Similarly, for the plant species in question, the diploid chromosome number is 20. This means there are 10 pairs of chromosomes. Having a diploid chromosome number allows genetic diversity due to the combination of chromosomes from both parents. Such occurrences are observable in organisms that reproduce sexually.

• Understanding Chromosome Sets: A complete set of chromosomes means having a chromosome from both maternal and paternal origins.
• Diploid in Sexual Reproduction: During reproduction, each parent contributes one set of chromosomes to the offspring, maintaining the diploid state.

Mitotic Prophase

Mitotic prophase is an early stage of mitosis, the process where a single cell divides into two identical daughter cells. During mitosis, the cells replicate their genetic content to distribute evenly into the two new cells. It ensures that the offspring will have the exact same DNA as the parent cell. Mitotic prophase plays a crucial role in preparing the chromosomes for this division. During this phase:

• The chromosomes condense and become more visible under a microscope. This makes the chromosomes appear X-shaped due to the presence of sister chromatids.
• Each chromosome has already been replicated during the preceding interphase.
• The nuclear envelope begins to break down, preparing for the later stages of mitosis where chromosomes are separated.

Understanding the process of mitotic prophase is vital for comprehending how cells maintain genetic information accurately during cell division.

Sister Chromatids

Sister chromatids are a critical part of the cell division process. Each chromatid represents a copy of a chromosome that is paired with its duplicate, joined together by a common centromere. These identical copies are produced during the S phase of the cell cycle in preparation for cell division. The presence of sister chromatids ensures:

• Accuracy in Cell Division: Because each chromatid is an exact copy of the other, they help ensure that each new cell receives the precise DNA information after cell division.
• Chromatid Separation: During cell division, specifically in anaphase, the sister chromatids are pulled apart and allocated to each of the two new daughter cells.
• Visualization During Prophase: As the cell prepares to divide, these chromatids make the chromosome appear thicker and easier to spot under a microscope.

In mitotic prophase, understanding the role of sister chromatids is essential to grasp how cells can reproduce effectively while maintaining genetic integrity.