Cell Division, Genetics, and Chromosomal Inheritance: Study Guide (Chapters 9–14)

Cell Division and the Cell Cycle

Genome and Chromosomes

The genome is the complete set of genetic material in an organism. In bacteria (prokaryotes), the genome is typically a single circular DNA molecule. In humans and other eukaryotes, the genome consists of multiple linear DNA molecules organized into chromosomes.

• Bacterial genome: Usually one circular DNA molecule.

• Human genome: 46 chromosomes (23 pairs), each a linear DNA molecule.

Prokaryotic Cell Division: Binary Fission

Prokaryotes reproduce by binary fission, a simple process where the cell duplicates its DNA and divides into two identical cells.

• DNA replication begins at the origin of replication.

• The cell elongates, and the plasma membrane grows inward, dividing the cell.

Nucleus Structure and Chromatin

• Nucleus: Contains the cell's genetic material.

• Nucleolus: Site of ribosomal RNA synthesis.

• Nuclear membrane: Double membrane enclosing the nucleus.

• Chromatin: DNA and protein complex; less condensed form of genetic material.

• Chromosomes: Condensed chromatin visible during cell division.

Difference: Chromatin is the uncondensed form; chromosomes are condensed for cell division.

Human Karyotype

A karyotype is an organized profile of an individual's chromosomes. Humans have 22 pairs of autosomes and 1 pair of sex chromosomes (XX or XY).

Chromosome Vocabulary

• Chromosome: One DNA molecule (or two sister chromatids after replication).

• Sister chromatids: Identical copies of a chromosome, joined at the centromere.

• Haploid (n): One set of chromosomes (e.g., gametes).

• Diploid (2n): Two sets of chromosomes (e.g., somatic cells).

• Homologous chromosomes: Chromosome pairs with the same genes but possibly different alleles.

The Cell Cycle

The cell cycle is the series of events that cells go through as they grow and divide.

• Interphase: Cell grows, replicates DNA (G1, S, G2 phases).

• Mitosis (M phase): Division of the nucleus.

• Cytokinesis: Division of the cytoplasm.

Mitosis Overview and Stages (PMAT)

Mitosis is the process by which a cell divides its nucleus and contents.

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at the metaphase plate.

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

• Telophase: Nuclear envelopes reform, chromosomes decondense.

Plant vs. Animal Mitosis

• Plant cells: Form a cell plate during cytokinesis.

• Animal cells: Form a cleavage furrow during cytokinesis.

Importance of Mitosis

• Growth of multicellular organisms

• Repair of damaged tissues

• Asexual reproduction in some organisms

Mitosis vs. Meiosis

• Mitosis: Produces two genetically identical diploid cells.

• Meiosis: Produces four genetically unique haploid cells (gametes).

Meiosis and Sexual Life Cycles

Chromosome Vocabulary (Extended)

• Fertilization: Fusion of gametes to form a zygote.

• Zygote: Fertilized egg cell (diploid).

• Autosomes: Non-sex chromosomes (pairs 1–22 in humans).

• Sex chromosomes: X and Y chromosomes determining biological sex.

Meiosis Overview and Stages

Meiosis is a two-division process that reduces chromosome number by half, producing gametes.

• Meiosis I: Homologous chromosomes separate.

• Meiosis II: Sister chromatids separate.

Genetic Diversity in Meiosis

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

• Independent Assortment: Random orientation of homologous pairs during metaphase I.

Importance of Meiosis

• Produces genetic variation in offspring

• Reduces chromosome number for sexual reproduction

Meiosis I vs. Meiosis II

• Meiosis I: Homologous chromosomes separate, chromosome number is halved.

• Meiosis II: Sister chromatids separate, similar to mitosis.

Location and Timing of Mitosis and Meiosis

• Mitosis: Occurs in somatic (body) cells throughout life.

• Meiosis: Occurs in germ cells (testes/ovaries) to produce gametes.

Gamete Formation in Humans

• Spermatogenesis: Formation of sperm in males.

• Oogenesis: Formation of eggs in females.

• Primary and secondary stages refer to the developmental steps of gametes.

Sex Determination

• Autosomes: Chromosomes not involved in sex determination.

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

Chromosomal Abnormalities (Section 12.4)

Normal X & Y Chromosome Characteristics

• X chromosome: Larger, contains many genes.

• Y chromosome: Smaller, contains genes for male development.

Aneuploidy: Abnormal Chromosome Number

• Aneuploidy: Abnormal number of chromosomes due to nondisjunction.

• Monosomy: Missing one chromosome (2n-1).

• Trisomy: Extra chromosome (2n+1).

Examples of Chromosomal Disorders

Disorder	Chromosomal Change	Main Features
Trisomy 21 (Down Syndrome)	Extra chromosome 21	Intellectual disability, characteristic facial features
Turner Syndrome	Monosomy X (XO)	Female, short stature, infertility
Klinefelter Syndrome	XXY	Male, tall, reduced fertility
Triple X (Poly-X)	XXX	Female, usually normal phenotype
Jacobs Syndrome	XYY	Male, tall, often normal phenotype

Molecular Basis of Inheritance (Chapters 13–14)

Functions of Genetic Material

• Stores hereditary information

• Directs synthesis of proteins

• Replicates for cell division

Chargaff's Rules

• In DNA, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C).

• Expressed as: $\text{A} = \text{T}$ and $\text{G} = \text{C}$

Structure of DNA (Watson & Crick Model)

• Double helix with two antiparallel strands

• Sugar-phosphate backbone on the outside, nitrogenous bases on the inside

• Bases paired by hydrogen bonds: A with T, G with C

DNA Replication

• Semiconservative process: each new DNA molecule has one old and one new strand

• Occurs in both prokaryotes and eukaryotes, but with differences in origin sites and complexity

DNA vs. RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Strands	Double-stranded	Single-stranded
Function	Genetic storage	Protein synthesis, regulation

Protein Synthesis: Transcription and Translation

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

• Translation: RNA is used to assemble amino acids into a protein.

• Participants: mRNA (messenger), tRNA (transfer), rRNA (ribosomal), ribosomes, amino acids.

DNA to Protein: Sequence Conversion

• Replication: DNA → DNA (complementary base pairing)

• Transcription: DNA → RNA (A pairs with U in RNA)

• Translation: RNA codons → amino acids (using genetic code table)

Example: If DNA template is 3'-TAC-5', RNA is 5'-AUG-3', which codes for methionine.

Mutations and Their Effects

• Mutation: Change in DNA sequence

• Can alter protein structure and function

• Point mutations: single base changes (e.g., sickle cell anemia)

Promoters and Terminators in Transcription

• Promoter: DNA sequence where RNA polymerase binds to start transcription

• Terminator: Sequence signaling the end of transcription

Gene Mutations and the Central Dogma

• Mutations in DNA can change the RNA and thus the protein sequence

• Central Dogma: DNA → RNA → Protein

Mutagens

• Mutagen: Physical or chemical agent that increases mutation rate (e.g., UV light, chemicals)

Additional info: Where specific diagrams or figures are referenced (e.g., "Table in Fig 14.6 p 293"), students should consult their textbook for the genetic code table to practice translation problems. All key terms and processes are explained in context for self-contained study.