Chapter 8: The Cellular Basis of Reproduction and Inheritance – Study Guide

Cell Division: Functions and Importance

Functions of Cell Division

Cell division is a fundamental biological process essential for the growth, maintenance, and reproduction of all living organisms.

• Growth: Enables organisms to increase in size by producing new cells.

• Repair and Maintenance: Replaces damaged or dead cells to maintain tissue health.

• Reproduction: Facilitates both asexual and sexual reproduction, ensuring continuity of life.

• Example: Skin cells divide to heal wounds; bacteria divide to reproduce.

Cell Division in Prokaryotes vs. Eukaryotes

Comparison of Cell Division Mechanisms

Prokaryotes and eukaryotes utilize distinct mechanisms for cell division, reflecting their structural differences.

• Prokaryotes: Divide by binary fission, a simple process involving DNA replication and cell splitting.

• Eukaryotes: Divide by mitosis (for somatic cells) and meiosis (for gametes), involving complex chromosome segregation.

• Contrast: Eukaryotic cells have multiple chromosomes and a nucleus; prokaryotes have a single circular chromosome and no nucleus.

Chromosome Structure and Key Terms

Definitions and Examples

• Chromatin: DNA and protein complex forming chromosomes; loosely packed during interphase.

• Sister Chromatids: Identical copies of a chromosome joined at the centromere after DNA replication.

• Centromere: Region where sister chromatids are attached; essential for chromosome movement.

• Replicated Chromosome: Chromosome consisting of two sister chromatids.

• Unreplicated Chromosome: Single chromatid chromosome before DNA replication.

• Example: During metaphase, chromosomes are replicated; after anaphase, they are unreplicated.

Structure of a Replicated Eukaryotic Chromosome

• Consists of two sister chromatids joined at the centromere.

• Made of DNA (genetic information) and proteins (structural support and regulation).

Biochemical Composition of Chromosomes

Main Biochemicals

• DNA: Stores genetic information.

• Proteins (histones): Package DNA and regulate gene expression.

Stages of the Eukaryotic Cell Cycle

Cell Cycle Overview

The eukaryotic cell cycle consists of interphase and the mitotic phase, each with distinct stages.

• Interphase: Includes G1 (growth), S (DNA synthesis), and G2 (preparation for division).

• Mitosis: Prophase, prometaphase, metaphase, anaphase, telophase.

• Cytokinesis: Division of cytoplasm.

• Chromosome Replication: Occurs during S phase; chromosomes are replicated in mitosis until anaphase.

Mitosis and Cytokinesis in Animal vs. Plant Cells

Comparison of Processes

• Mitosis: Similar stages in both, but plant cells lack centrioles.

• Cytokinesis: Animal cells form a cleavage furrow; plant cells build a cell plate.

• Example: Animal cell division results in two daughter cells; plant cell division forms a new cell wall.

Control of Cell Division

Cell Cycle Regulation

• Controlled by checkpoints (G1, G2, M) and regulatory proteins (cyclins, CDKs).

• Ensures proper DNA replication and division.

• Example: If DNA is damaged, cell cycle may pause for repair.

Consequences of Cell Cycle Errors

Potential Outcomes

• Cancer: Uncontrolled cell division due to checkpoint failure.

• Genetic Disorders: Errors in chromosome segregation can cause conditions like Down syndrome.

Asexual vs. Sexual Reproduction

Comparison and Key Processes

• Asexual Reproduction: Offspring are genetically identical to parent; involves mitosis.

• Sexual Reproduction: Offspring are genetically diverse; involves meiosis and fertilization.

• Universal Processes: Meiosis and fertilization are found in all sexual life cycles.

Key Terms in Sexual Reproduction

Definitions and Examples

• Homologous Chromosomes: Chromosome pairs with similar genes; one from each parent.

• Haploid (n): Single set of chromosomes; gametes.

• Diploid (2n): Two sets of chromosomes; somatic cells.

• Tetrad: Four chromatids formed during meiosis I.

• Crossing Over: Exchange of genetic material between nonsister chromatids.

• Nonsister Chromatids: Chromatids from homologous chromosomes.

• Independent Assortment: Random distribution of chromosomes during meiosis.

• Gamete: Sex cell (egg or sperm).

• Egg/Ovum: Female gamete.

• Sperm: Male gamete.

• Spore: Reproductive cell in plants and fungi.

• Zygote: Fertilized egg; diploid.

Meiosis: Purpose and Stages

Purpose of Meiosis

• Reduces chromosome number by half, producing haploid gametes.

• Ensures genetic diversity.

Stages of Meiosis

• Meiosis I: Prophase I, metaphase I, anaphase I, telophase I.

• Meiosis II: Prophase II, metaphase II, anaphase II, telophase II.

• Each stage involves specific chromosome movements and segregation.

Genetic Variability in Meiosis

Sources of Variability

• Crossing Over: Occurs during prophase I; creates new allele combinations.

• Independent Assortment: Random distribution of homologous chromosomes during metaphase I.

Consequences of Errors in Meiosis

Potential Outcomes

• Aneuploidy: Abnormal chromosome number (e.g., trisomy 21).

• Infertility: Errors can prevent viable gamete formation.

Animal and Plant Life Cycles

Typical Life Cycle Outline

• Animal Life Cycle: Fertilization (forms zygote), mitosis (growth), meiosis (gamete production).

• Plant Life Cycle: Alternation of generations; mitosis (growth), meiosis (spore production), fertilization (forms zygote).

Comparison of Mitosis and Meiosis

Unity within Diversity

• Mitosis: Produces identical cells; used for growth and repair.

• Meiosis: Produces genetically diverse gametes; used for sexual reproduction.

• Unity: Both processes involve chromosome segregation.

• Diversity: Meiosis introduces genetic variation.

Summary Table: Mitosis vs. Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2	4
Chromosome Number	Diploid (2n)	Haploid (n)
Genetic Variation	None	Yes
Function	Growth, repair	Sexual reproduction