Chapter 8

Cellular Reproduction: Cells from Cells

Purpose of Cell Division

• Growth: Cell division allows multicellular organisms to grow by increasing the number of cells.

• Repair: Damaged or dead cells are replaced through cell division.

• Reproduction: Cell division is essential for both asexual and sexual reproduction.

• Asexual Reproduction: Offspring are produced by a single parent without the involvement of gametes; offspring are genetically identical to the parent.

• Sexual Reproduction: Involves the fusion of gametes (egg and sperm), resulting in genetically unique offspring.

Chromosome Structure

• Chromosome: A long DNA molecule with associated proteins, carrying genetic information.

• DNA: Deoxyribonucleic acid, the hereditary material in all living organisms.

• Chromatid: Each of the two identical halves of a duplicated chromosome.

• Sister Chromatids: Two identical chromatids joined at a region called the centromere.

• Centromere: The region where sister chromatids are attached and where spindle fibers attach during cell division.

The Cell Cycle

• G1 Phase (First Gap): Cell grows and carries out normal functions.

• S Phase (Synthesis): DNA is replicated, resulting in two sister chromatids per chromosome.

• G2 Phase (Second Gap): Cell prepares for division by producing proteins and organelles.

• M Phase (Mitosis): Division of the nucleus and cytoplasm to form two daughter cells.

Stages of Mitosis

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

• Metaphase: Chromosomes align at the cell's equator (metaphase plate).

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

• Telophase: Nuclear envelopes reform around the chromosomes, which decondense.

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

Control of the Cell Cycle and Cancer

• Cell Cycle Control: Regulated by checkpoints (G1, G2, M) that ensure proper division.

• Cancer: Results from loss of cell cycle control, leading to uncontrolled cell division.

• Benign Tumor: Abnormal mass of cells that remains at its original site.

• Malignant Tumor: Mass of cancerous cells that can invade surrounding tissues.

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

Diploid vs. Haploid Cells

• Diploid (2n): Cells with two sets of chromosomes (one from each parent); typical of somatic cells.

• Haploid (n): Cells with one set of chromosomes; typical of gametes (sperm and egg).

Mitosis vs. Meiosis

Genetic Variation in Meiosis

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

• Crossing Over: Exchange of genetic material between homologous chromosomes during prophase I.

Nondisjunction

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

• Example: Down syndrome (trisomy 21) results from an extra copy of chromosome 21.

Chapter 9

Patterns of Inheritance

Mendel’s Experiments and Principles

• Gregor Mendel: Discovered the basic principles of heredity using pea plants.

• Gene: A unit of heredity that encodes a specific trait.

• Allele: Different forms of a gene.

• Dominant Allele: Expressed when present

  (represented by uppercase letter).

• Recessive Allele: Expressed only when two copies are present (lowercase letter).

• Homozygous: Having two identical alleles for a gene (e.g., AA or aa).

• Heterozygous: Having two different alleles for a gene (e.g., Aa).

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

• Phenotype: Observable traits of an organism.

Mendel’s Laws

• Law of Segregation: Alleles separate during gamete formation and reunite at fertilization.

• Law of Independent Assortment: The inheritance of one trait is generally independent of another trait.

Punnett Squares

• Used to predict the genotypes and phenotypes of offspring from genetic crosses.

• Example: Crossing two heterozygous pea plants (Aa x Aa) yields a 3:1 ratio of dominant to recessive phenotypes.

Pedigrees and Human Inheritance

• Pedigree: Diagram showing inheritance patterns in families.

• Carrier: Individual who is heterozygous for a recessive disorder but does not show symptoms.

• Recessive Disorders: Require two copies of the mutant allele (e.g., cystic fibrosis).

• Dominant Disorders: Require only one copy of the mutant allele (e.g., Huntington's disease).

Exceptions to Mendelian Inheritance

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white flowers produce pink).

• Codominance: Both alleles are fully expressed in heterozygotes (e.g., AB blood type).

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

• Sex-Linked Inheritance: Genes located on sex chromosomes (e.g., color blindness).

Chapter 10

The Structure and Function of DNA

DNA Structure

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

• Sugar-Phosphate Backbone: Alternating sugars and phosphates form the sides of the DNA ladder.

• Nitrogenous Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

DNA Double Helix and Base Pairing

• DNA forms a double helix with complementary base pairing:

• A pairs with T, and C pairs with G.

• Base-Pairing Rule: ,

DNA vs. RNA

DNA Replication

• DNA is copied before cell division.

• DNA Polymerase: Enzyme that adds complementary nucleotides to the growing DNA strand.

• Complementary Base Pairing: Ensures accurate copying of genetic information.

Central Dogma: DNA → RNA → Protein

• Transcription: DNA is used as a template to make messenger RNA (mRNA).

• Translation: mRNA is decoded by ribosomes to build a protein.

• Codon: A sequence of three mRNA bases that specifies an amino acid.

• Genetic Code: Universal set of codons that determine amino acid sequence.

Roles in Protein Synthesis

• mRNA (messenger RNA): Carries genetic information from DNA to ribosomes.

• tRNA (transfer RNA): Brings amino acids to the ribosome during translation.

• Ribosomes: Sites of protein synthesis, composed of rRNA and proteins.

Mutations

• Mutation: Any change in the DNA sequence.

• Substitution: One base is replaced by another; may change one amino acid.

• Insertion: Addition of one or more bases; can cause frameshift.

• Deletion: Removal of one or more bases; can cause frameshift.

• Frameshift Mutation: Insertion or deletion that alters the reading frame, often resulting in nonfunctional proteins.