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 vs. Sexual Reproduction

Asexual Reproduction: Offspring are genetically identical to the parent; involves a single parent (e.g., binary fission in bacteria, mitosis in plants).

Sexual Reproduction: Offspring inherit a combination of genes from two parents, resulting in genetic variation; involves meiosis and fertilization.

Chromosome Structure

DNA: The molecule that stores genetic information.

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.

The Cell Cycle

G1 Phase: Cell grows and carries out normal functions.

S Phase: DNA is replicated.

G2 Phase: Cell prepares for division.

M Phase (Mitosis): Division of the nucleus and cytoplasm.

Stages of Mitosis

Prophase: Chromosomes condense, spindle forms, 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.

Control of the Cell Cycle and Cancer

Cell Cycle Control: Regulated by checkpoints and proteins (e.g., cyclins).

Cancer: Uncontrolled cell division due to loss of cell cycle regulation.

Benign Tumors: Non-cancerous, do not spread.

Malignant Tumors: Cancerous, can invade nearby tissues.

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

Diploid vs. Haploid Cells

Diploid (2n): Cells with two sets of chromosomes (e.g., somatic cells).

Haploid (n): Cells with one set of chromosomes (e.g., gametes).

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

Definition: Failure of chromosomes to separate properly during meiosis.

Result: Gametes with abnormal chromosome numbers (e.g., trisomy 21 causes Down syndrome).

Chapter 9

Patterns of Inheritance

Mendel’s Experiments and Principles

Gregor Mendel: Studied inheritance using pea plants.

Gene: Unit of heredity; segment of DNA coding for a trait.

Allele: Different forms of a gene.

Dominant Allele: Expressed if present (represented by uppercase letter).

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

Homozygous: Two identical alleles (e.g., AA or aa).

Heterozygous: Two different alleles (e.g., Aa).

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

Phenotype: Observable traits (e.g., purple flowers).

Mendel’s Laws

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

Law of Independent Assortment: Inheritance of one trait is generally independent of another.

Punnett Squares

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

Example: Crossing Aa x Aa for a single trait yields a 3:1 phenotypic ratio.

Pedigrees and Human Inheritance

Pedigree: Diagram showing inheritance patterns in families.

Carrier: Individual who has one copy of a recessive allele but does not express the trait.

Genetic Disorders

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., pink flowers from red and white parents).

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

Polygenic Inheritance: Multiple genes influence a 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 structure.

Base Pairing Rules: A pairs with T, C pairs with G.

DNA vs. RNA

DNA Replication

DNA is copied before cell division.

DNA Polymerase: Enzyme that adds complementary nucleotides.

Complementary Base Pairing: Ensures accurate copying of genetic information.

Central Dogma: DNA → RNA → Protein

Transcription: DNA is used as a template to make RNA.

Translation: RNA is used to assemble amino acids into proteins.

Genetic Code and Codons

Codon: Sequence of three RNA bases that codes for a specific amino acid.

The genetic code is universal and redundant.

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.

Mutations

Mutation: Change in the DNA sequence.

Substitution: One base is replaced by another.

Insertion: Extra base is added.

Deletion: Base is removed.

Frameshift Mutation: Insertion or deletion that alters the reading frame, often with severe effects on the protein.