Biology: Cells to AP Biology · Module 4 of 15
Cell Division & Reproduction
How cells copy and divide themselves, why sex cells are made differently, and what happens when division goes wrong.
The Cell Cycle & Mitosis
- The cell cycle has three main stages: interphase (cell grows, copies DNA), mitosis (nucleus divides), and cytokinesis (cytoplasm divides).
- Mitosis has four phases — prophase, metaphase, anaphase, telophase (PMAT) — that separate duplicated chromosomes into two identical nuclei.
- Mitosis produces two genetically identical daughter cells, used for growth and repair.
During which phase of mitosis do sister chromatids separate and move to opposite poles of the cell?
Solution. Anaphase.
Meiosis & Genetic Variation
- Meiosis produces four genetically different haploid cells (gametes) from one diploid cell, through two rounds of division.
- Crossing over (exchange of DNA between homologous chromosomes) and independent assortment during meiosis I create genetic variation.
Why are siblings genetically different from each other even though they share the same parents?
Solution. Crossing over and independent assortment during meiosis shuffle genetic material differently each time gametes are formed, so each egg or sperm is genetically unique.
Sexual vs. Asexual Reproduction
- Asexual reproduction (e.g. binary fission, budding) produces genetically identical offspring from one parent, quickly and without a mate.
- Sexual reproduction combines genetic material from two parents, producing genetically varied offspring, which can be an evolutionary advantage in changing environments.
Which type of reproduction would be more advantageous for a population facing a rapidly changing environment, and why?
Solution. Sexual reproduction, because it creates more genetic variation, increasing the chance some offspring have traits that let them survive the new threat.
Cancer: Uncontrolled Cell Division
- Cancer results from mutations that disrupt the normal controls (checkpoints) on the cell cycle, causing cells to divide uncontrollably.
- Tumor suppressor genes normally slow or stop cell division; when they're damaged or deactivated, cells can divide unchecked.
How does cancer relate to the normal process of mitosis?
Solution. Cancer cells still use the same basic mitosis machinery, but mutations disable the normal checkpoints that regulate when and how often the cell cycle occurs, so division happens uncontrolled.
Check yourself
2 of this module's 5 quiz questions. Pick your answers, then check them in the app, with an explanation for every question.
1. What process produces two genetically identical daughter cells?
2. How many daughter cells does meiosis produce, and are they genetically identical?