BIO 222 Chapter 2: Chromosomes and Reproduction

Chapter 2: Chromosomes and Cellular Reproduction

• The chapter covers prokaryotic and eukaryotic cells, cell reproduction, and sexual reproduction.
• A prokaryotic cell lacks a nucleus and membrane-bound organelles. Its DNA is circular and not complexed with histones. Prokaryotes include bacteria and archaea.
• Eukaryotic cells contain a nucleus and membrane-bound organelles. Their DNA is linear and complexed with histones to form chromosomes.
• Prokaryotic cell division is simple division, separating replicated circular chromosomes from the origin of replication. It has a high rate of replication
• Eukaryotic cell replication involves homologous pairs, chromosome structure, and the cell cycle.

Eukaryotic Chromosomes

• Homologous pairs: Diploid cells carry two sets of genetic information, with each set having similar chromosomes. Humans have 23 pairs.
• Chromosome structure: At times, a chromosome consists of one chromatid, and at others, it consists of two sister chromatids. The centromere is the attachment point for spindle microtubules. The telomeres are the stable ends of chromosomes. Different types of chromosomes include submetacentric, metacentric, telocentric, and acrocentric.
• Cell cycle: The cell grows, replicates DNA, and divides. Key transition points are the checkpoints: G1/S, G2/M. The cell cycle includes phases like G0, G1, S, G2, Mitosis (prophase, prometaphase, metaphase, anaphase, telophase), and Cytokinesis.

Prokaryotic Cell Reproduction

• Simple division: Prokaryotic cells divide by separating replicated circular chromosomes from an origin of replication. The process happens at a high rate.

Eukaryotic Cell Replication

• Cell cycle phases: G1: growth and development; S: DNA synthesis; G2: preparation for cell division. The cell cycle also includes mitosis (prophase, prometaphase, metaphase, anaphase, telophase) and cytokinesis. Mitosis is the active division of the nucleus and cytokinesis is the division of the cytoplasm. Multiple checkpoints regulate progression through the cell cycle
• Genetic consequences of the cell cycle: The cycle produces two cells genetically identical to each other and to the original cell. Each new cell has a full complement of chromosomes.
• The process occurs at a high rate of replication.
• The mitosis phases are discussed as prophase, metaphase, anaphase, and telophase.
• The mitosis separation of sister chromatids and homologous chromosomes involves an important protein: Cohesin.
• Two types of cell divisions are covered: Mitosis (used for growth and repair in somatic cells) and Meiosis (used to produce gametes).

Meiosis

• Meiosis: The production of haploid gametes. Meiotic events include interphase (DNA synthesis and chromosome replication), Meiosis I (separation of homologous chromosome pairs), and Meiosis II (separation of sister chromatids). Each meiosis cycle has four phases: prophase, metaphase, anaphase, telophase. Interkinesis is an intermediate phase between meiosis 1 and 2
• Crossing over: Crossing over of chromosome segments takes place during prophase I; this is the first mechanism of generating genetic variation.
• Genetic variation: The random alignment of homologous chromosome pairs in meiosis I and crossing over in prophase I create genetic variation in gametes. Genetic variation ensures diversity.
• Interkinesis: An intermediate phase occurring between meiosis 1 and 2
• Meiosis: Meiosis has been described as a haploid cell division which results in four cells from a single cell

Meiosis in the Life Cycle of Animals and Plants

• Spermatogenesis: Male gamete production.
• Oogenesis: Female gamete production.
• Gametes are haploid reproductive cells.
• Meiosis in plants: Plants often have different life cycles than animals in which the stages alternate between a single-celled haploid form and a multicellular diploid form. These terms are sporophyte (diploid form) and gametophyte (haploid form

Viruses

• Viruses lack both prokaryotic or eukaryotic characteristics and are surrounded by an outer protein coat that encompasses the nucleic acid.