Chromosome transmission

Chromosomal Transmission

Overview of Chromosome Transmission

• Chromosomes are critical structures that contain genetic material within living cells.

• They consist of DNA and proteins, forming chromatin in eukaryotic cells.

• This transmission occurs during cell division and sexual reproduction.

General Features of Chromosomes

• Chromosomes contain genes which encode information necessary for the organism's traits.

• Composed biochemically of:

  • DNA: The genetic material.

  • Proteins: Provide structural organization.

• Eukaryotic cells possess linear chromosomes, while prokaryotic cells generally have a single circular chromosome.

Types of Cells

• Prokaryotes: Include Bacteria and Archaea.

• Eukaryotes: Encompass Protists, fungi, plants, and animals.

Features of Prokaryotic Cells

• Lack a nucleus; DNA is found in a region called the nucleoid.

• Typically consist of a single circular chromosome.

• Enclosed by a plasma membrane and often have a rigid cell wall; some may also possess an outer membrane or a flagellum.

Features of Eukaryotic Cells

• Eukaryotes contain a membrane-bound nucleus housing most of their genetic material as linear chromosomes.

• Possess specialized membrane-bounded organelles:

  • Mitochondria: Energy production via ATP synthesis; contain their own DNA.

  • Lysosomes: Involved in degradation of macromolecules.

  • Golgi Apparatus: Modifies and traffics proteins.

Types of Animal Cells

• Somatic Cells: Non-germ body cells such as blood cells.

• Germ Cells: Gametes including sperm and egg cells.

Cytogenetics

• Study of chromosomes microscopically; useful for detecting chromosomal abnormalities.

• A karyotype provides an organized representation of an organism's chromosomes, usually arranged from largest to smallest.

Karyotype Preparation

• Blood samples are treated to stimulate division, and colchicine is applied to halt mitosis for observation of compacted chromosomes.

• Cells are centrifuged and swollen in a hypotonic solution, fixed, stained, and examined under a microscope.

Diploid Human Karyotype

• A diploid human cell has two complete sets of chromosomes, totaling 46 (23 pairs).

• Many species exhibit diploidy, with examples:

  • Humans: 46 chromosomes (23 pairs).

  • Dogs: 78 chromosomes (39 pairs).

  • Fruit flies: 8 chromosomes (4 pairs).

Inheritance of Eukaryotic Chromosomes

• Chromosomal pairs are homologs; each homolog is similar in size, shape, and gene content, but may differ in alleles.

• The sex chromosomes X and Y differ in size and genetic content; they only share small homologous regions.

Genotypic Composition

• Genotype Examples:

  • AA: Homozygous dominant.

  • Bb: Heterozygous.

  • cc: Homozygous recessive.

Cell Division

• A primary function of cell division involves asexual reproduction, particularly in unicellular organisms (e.g., bacteria, amoeba, yeast).

• Eukaryotic cell multiplication contributes to the development of multicellularity, as seen in multicellular organisms originating from a single fertilized egg.

Process of Prokaryotic Cell Division

• Prokaryotic cells reproduce asexually through binary fission, where the bacterial chromosome replicates.

The Eukaryotic Cell Cycle

• Eukaryotic cell division is more complex, involving phases of the cell cycle: Interphase (G1, S, G2) and M phase (Mitosis).

Interphase Details

• Cells spend a significant period in interphase preparing for division; includes:

  • G1 Phase: Preparation for division; restriction point determination.

  • S Phase: Chromosomes replicate.

  • G2 Phase: Material accumulation for division.

Mitosis and its Phases

• Mitosis ensures that each daughter cell receives an identical complement of chromosomes:

  • Phases include:

    • Prophase: Chromatids condense; nuclear envelope dissociates.

    • Prometaphase: Spindle apparatus forms; sister chromatids are captured.

    • Metaphase: Chromatids align at the metaphase plate.

    • Anaphase: Sister chromatids separate to opposite poles.

    • Telophase: Chromosomes decondense, and nuclear membranes reform.

Cytokinesis

• Follows mitosis, dividing the cytoplasm;

  • In Animals: A cleavage furrow forms.

  • In Plants: A cell plate forms.

Outcome of Cell Division

• Results in two genetically identical daughter cells, maintaining genetic consistency and enabling multicellularity.