Mitosis vs. Meiosis: Cell Division for Growth and Reproduction

Exam Tip: If a question asks about "body cells," think mitosis. If it asks about "sex cells" or "gametes," think meiosis.

Genetic Makeup: Diploid vs. Haploid

One of the most critical distinctions between these processes is the "genetic math" involved. We describe cells based on their number of sets of chromosomes.

• Diploid (2n): Cells that contain two complete sets of chromosomes—one set from each parent. Most somatic cells are diploid.
• Haploid (n): Cells that contain only one set of chromosomes. Gametes are haploid.

Mitosis Outcomes

In mitosis, a single diploid cell ($2n$) divides to produce two daughter cells that are also diploid ($2n$). These daughter cells are genetically identical to the parent cell and to each other. This ensures that every new skin cell has the exact same instructions as the old one.

Meiosis Outcomes

Meiosis is more complex. It involves two rounds of division (Meiosis I and Meiosis II) but only one round of DNA replication. This results in four daughter cells, each of which is haploid ($n$). Furthermore, these cells are genetically unique due to processes like crossing over, which ensures that no two gametes are exactly the same.

Summary Comparison Table

To help visualize these differences, refer to the following comparison:

Worked Example: Calculating Gametes

In biology exams, you may be asked to determine the genetic makeup of gametes based on a parent's genotype.

Scenario: A plant has a genotype of $Aa$ (heterozygous) for a specific trait. If this plant undergoes mitosis, what are the genotypes of the resulting cells? If it undergoes meiosis, what are the possible genotypes of the resulting gametes?

Solution:

1. Mitosis: Since mitosis creates identical copies, the daughter cells will maintain the same genotype as the parent. $\text{Result: } Aa \text{ and } Aa$
2. Meiosis: Meiosis separates the alleles (the versions of the gene) so that each gamete only gets one. $\text{Result: } A \text{ and } a$

Key Terminology Reminder:

• Chromatin: The loose, "spaghetti-like" form of DNA.
• Chromosome: The tightly coiled, organized structure of DNA.
• Chromatid: One half of a replicated chromosome.
• Autosome: Any chromosome that is not a sex chromosome.

By mastering these distinctions, you can navigate complex questions regarding inheritance patterns, such as complete dominance or X-linkage, because you will understand exactly how the underlying cells are passing on their genetic information.