JC genetics chapter 2

Chapter 02: Chromosome Transmission During Cell Division and Sexual Reproduction

  • Copyright: Robert J. Brooker © McGraw Hill LLC. All rights reserved.

Introduction

  • Cellular replication is essential for transmitting genetic information.

2.1 General Features of Chromosomes

  • Composition: Chromosomes consist of DNA and proteins.

    • DNA contains genetic information.

    • Proteins provide structural support to DNA.

  • In eukaryotes, the DNA-protein complex is termed chromatin.

2.2 Types of Cells

  • Prokaryotic Cells:

    • Include Bacteria and Archaea.

  • Eukaryotic Cells:

    • Include Protists, fungi, plants, and animals.

2.2.1 Prokaryotic Cell Features

  • Components:

    • Outer membrane, cell wall, plasma membrane, ribosomes, nucleoid (location of bacterial chromosome), and flagellum.

2.2.2 Eukaryotic Cell Features

  • Key components include:

    • Mitochondria, Golgi body, rough and smooth endoplasmic reticulum, nucleolus, and lysosomes.

2.3 Types of Animal Cells

  • Somatic Cells:

    • Body cells, excluding gametes (e.g., blood cells).

  • Germ Cells:

    • Gametes, including sperm and egg cells.

Cytogenetics

  • The study focusing on the microscopic examination of chromosomes (cytogenetics).

    • Chromosomal analysis can detect abnormalities.

    • A karyotype is an organized visual representation of chromosomes sorted by size.

2.4 Eukaryotic Chromosomes

  • Diploid Nature: Most species are diploid, possessing two sets of chromosomes.

    • Examples: Humans (46 chromosomes), dogs (78 chromosomes), fruit flies (8 chromosomes).

  • Homologous Chromosomes:

    • Pairs of chromosomes that are nearly identical in size and gene content but may differ in alleles.

2.5 Cell Division

  • Asexual Reproduction: Occurs in unicellular organisms (e.g., bacteria, amoeba, yeast).

  • Eukaryotic cells undergo a complex cell cycle prior to division.

    • Phases: G1, S (replication), G2, M (Mitosis).

2.5.1 Mitosis

  • Defined as the process producing two genetically identical daughter cells:

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

    • Each daughter cell receives the same complement of chromosomes (46 in humans).

2.6 Meiosis

  • Sexual Reproduction: Involves the creation of haploid gametes from diploid parent cells.

  • Meiosis Stages:

    • Involves Meiosis I and II, allowing for genetic diversity through crossing over and independent assortment.

    • Produces four genetically distinct haploid daughter cells.

2.7 Gamete Formation

  • Spermatogenesis: The formation of sperm in the testes.

    • Includes a diploid cell dividing to produce primary spermatocytes through meiosis.

  • Oogenesis: The formation of egg cells in ovaries.

    • Involves asymmetric division producing polar bodies.

Environmental Influence on Sex Determination

  • Sex determination can also be influenced by environmental factors, such as temperature in reptiles and behavioral changes in clownfish.

2.8 Sex Chromosomes and Determination

  • XX fo females and XY for males; variations in other species include ZW and haplodiploid systems in bees.

Conclusion

  • This chapter summarizes the mechanisms of chromosome transmission during cell division, highlights differences between mitosis and meiosis, and explains the processes involved in sexual reproduction.