Cell Division and Genetics

Cell Theory and Cell Division

The cell theory is a foundational concept in biology, stating that all living things are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells. Cell division is essential for growth, repair, and reproduction in organisms.

• Purposes of Cell Division: Growth, repair of damaged tissues, and reproduction.

• Sexual vs. Asexual Reproduction: Sexual reproduction involves two parents and produces genetically diverse offspring; asexual reproduction involves one parent and produces genetically identical offspring.

• Methods of Asexual Reproduction: Binary fission, budding, and fragmentation.

DNA, Genes, and Chromosomes

Genetic information is organized in DNA, which is packaged into chromosomes. Genes are segments of DNA that code for specific traits.

• DNA: The molecule that stores genetic information.

• Gene: A segment of DNA that codes for a protein or trait.

• Chromosome: A structure made of DNA and proteins; humans have 46 chromosomes in each somatic cell.

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

• Centromere: The region where sister chromatids are joined.

The Cell Cycle and Mitosis

The cell cycle consists of interphase (cell growth and DNA replication) and the mitotic phase (division of the nucleus and cytoplasm).

• Interphase: The longest phase; includes G1 (growth), S (DNA synthesis), and G2 (preparation for mitosis).

• Mitotic Phase: Includes mitosis (division of the nucleus) and cytokinesis (division of the cytoplasm).

• Chromosome Duplication: Occurs during S phase; ensures each daughter cell receives a complete set of chromosomes.

• Mitosis: Division of the nucleus into two genetically identical nuclei.

• Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Phases of Mitosis

• Prophase: Chromosomes condense, spindle fibers form, nuclear envelope breaks down.

• Metaphase: Chromosomes align at the cell's equator.

• Anaphase: Sister chromatids separate and move to opposite poles.

• Telophase: Nuclear envelopes reform, chromosomes decondense.

At the end of mitosis and cytokinesis, two genetically identical daughter cells are produced, each with the same number of chromosomes as the parent cell (46 in humans).

Cytokinesis in Plant vs. Animal Cells

• Animal Cells: Cytokinesis occurs via a cleavage furrow.

• Plant Cells: Cytokinesis occurs via formation of a cell plate.

Cloning and Cell Division

• Clone: An organism or cell produced asexually from one ancestor, genetically identical to the parent.

• Types of Cloning: Nuclear transplantation, plant cloning, reproductive cloning, and therapeutic cloning (stem cells) all involve mitotic division.

Meiosis and Sexual Reproduction

Meiosis is a type of cell division that reduces the chromosome number by half, producing gametes (sperm and egg).

• Gamete: A haploid sex cell (sperm or egg).

• Zygote: The diploid cell formed by the fusion of two gametes.

• Haploid (n): One set of chromosomes (23 in humans).

• Diploid (2n): Two sets of chromosomes (46 in humans).

• Homologous Chromosomes: Chromosome pairs, one from each parent, with the same genes but possibly different alleles.

• Karyotype: A display of an individual's complete set of chromosomes, used to detect chromosomal abnormalities.

• Sex Chromosomes: X and Y chromosomes; XX = female, XY = male.

Phases of Meiosis

• Meiosis I: Homologous chromosomes separate (Prophase I, Metaphase I, Anaphase I, Telophase I).

• Meiosis II: Sister chromatids separate (Prophase II, Metaphase II, Anaphase II, Telophase II).

• Meiosis produces four haploid cells from one diploid cell.

Comparison: Mitosis vs. Meiosis

Genetic Variation

• Independent Assortment: Random distribution of homologous chromosomes during meiosis.

• Random Fertilization: Any sperm can fertilize any egg.

• Crossing Over: Exchange of genetic material between homologous chromosomes during Prophase I of meiosis, increasing genetic diversity.

Nondisjunction and Chromosomal Disorders

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers.

• Trisomy 21 (Down Syndrome): Extra chromosome 21.

• Sex Chromosome Abnormalities: Triple-X syndrome (XXX), Jacob’s syndrome (XYY), Klinefelter’s syndrome (XXY), Turner’s syndrome (XO).

Basic Genetics and Inheritance

• Allele: Different forms of a gene.

• Dominant/Recessive Alleles: Dominant alleles mask recessive alleles in heterozygotes.

• Genotype: Genetic makeup (e.g., AA, Aa, aa).

• Phenotype: Observable traits.

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

• Monohybrid Cross: Cross between individuals heterozygous for one gene.

• Punnett Square: Tool to predict genotypic and phenotypic ratios.

• Test Cross: Cross between an individual with unknown genotype and a homozygous recessive individual to determine genotype.

Exceptions to Mendelian Genetics

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., red x white flowers = pink).

• Multiple Alleles: More than two alleles exist for a gene (e.g., blood types).

• Polygenic Inheritance: Multiple genes affect a single trait (e.g., skin color).

• Environmental Effects: Environment can influence gene expression (epigenetics).

• Carrier: Heterozygous individual carrying a recessive allele for a trait.

Sex-Linked Inheritance

• Sex-Linked Traits: Traits controlled by genes on sex chromosomes, often X-linked.

• Y Chromosome: Contains fewer genes; Y-linked traits are rare.

• Monohybrid Cross for Sex-Linked Traits: Use Punnett square with X and Y chromosomes.

Molecular Biology: DNA, RNA, and Protein Synthesis

Structure of DNA

• Double Helix: DNA is a double-stranded helix.

• Nucleotide: Building block of DNA, consisting of a phosphate, deoxyribose sugar, and nitrogenous base.

• Base Pairing: Adenine (A) pairs with Thymine (T), Cytosine (C) pairs with Guanine (G).

• Hydrogen Bonds: Hold the two DNA strands together.

• Complementary Sequence: Each strand can be used to reconstruct the other.

DNA vs. RNA

Transcription

• Definition: Process of copying DNA into messenger RNA (mRNA).

• Location: Nucleus.

• Product: mRNA, which carries genetic information to the cytoplasm.

• Base Pairing: A pairs with U in RNA, C with G.

Translation

• Definition: Conversion of mRNA sequence into a polypeptide (protein).

• Location: Ribosome in the cytoplasm.

• Types of RNA Involved:

  • mRNA: Carries genetic code from DNA.

  • tRNA: Brings amino acids to the ribosome; has an anticodon that pairs with mRNA codon.

  • rRNA: Forms part of the ribosome structure.

• Codon: Three-nucleotide sequence on mRNA that codes for an amino acid.

• Anticodon: Three-nucleotide sequence on tRNA complementary to mRNA codon.

• Start and Stop Codons: Specific sequences signal the beginning and end of translation.

Gene Regulation and Expression

• Gene Regulation: Mechanisms that control when and how genes are expressed.

• Gene Expression: The process by which information from a gene is used to synthesize a functional product (protein).

• Not all genes are active in all cells at all times; gene expression is regulated to meet cellular needs.

Mutations and Cancer

• Mutation: A change in the DNA sequence.

• Carcinogens: Substances that cause cancer, often by acting as mutagens (agents that cause mutations).

• Tumor: An abnormal mass of cells resulting from uncontrolled cell division.

• Cancer: Disease caused by malignant tumors that invade tissues and can metastasize (spread).

• Proto-oncogenes: Normal genes that promote cell division; can become oncogenes (cancer-causing) if mutated.

• Tumor-Suppressor Genes: Genes that inhibit cell division; mutations can lead to cancer.

• Growth Factors: Proteins that stimulate cell division.

Progression of Cancer

• Benign Tumor: Non-cancerous, does not spread.

• Malignant Tumor: Cancerous, can invade other tissues.

• Metastasis: Spread of cancer cells to other parts of the body.

• Prevention: Healthy lifestyle, avoiding carcinogens, regular screenings.

• Treatment: Surgery, radiation, chemotherapy, targeted therapies.

Biotechnology and Genetic Engineering

Biotechnology and Genetic Engineering

• Biotechnology: Use of living organisms or their products to modify or improve human health and environment.

• Genetic Engineering: Direct manipulation of an organism's genes using biotechnology.

• Restriction Enzymes: Enzymes that cut DNA at specific sequences, essential for genetic engineering.

• Plasmid: Small, circular DNA molecule in bacteria used as a vector to transfer genes (e.g., for producing human insulin).

CRISPR-Cas9

• CRISPR-Cas9: A precise gene-editing technology that can add, remove, or alter genetic material at particular locations in the genome.

Genetically Modified Organisms (GMOs)

• GMO: Organism whose genome has been altered using genetic engineering.

• Transgenic Organism: Organism that contains genes from another species.

• Transgenic Animals vs. Plants: Separated due to different methods and applications.

• Pros and Cons of GMOs: Pros include increased yield, pest resistance, and nutritional enhancement; cons include potential environmental and health risks (though no conclusive evidence of harm).

Examples of GMOs

• Bt Corn: Insect-resistant corn.

• Golden Rice: Rice engineered to produce vitamin A.

• GM Papaya: Resistant to papaya ringspot virus.

• GM Animals: Pigs, goats, and salmon with improved traits.

DNA Technology in Forensics

• PCR (Polymerase Chain Reaction): Technique to amplify specific DNA sequences.

• DNA Profiling: Matching DNA samples using short tandem repeats (STRs).

• STR Analysis: Examines specific regions of DNA for repeat patterns unique to individuals.

• Gel Electrophoresis: Technique to separate DNA fragments by size; shorter fragments move farther.

Proteomics

• Proteomics: The large-scale study of proteins, their structures, and functions; important for understanding gene expression and disease.

Additional info: Some modules and details were omitted from exam coverage as noted in the original guide. The above content focuses on the core concepts required for exam preparation.