Chptr+8-+Cellular+Reproduction+%28for+students%29

Cellular Reproduction

• Cells from Cells: The fundamental principle of cellular reproduction is that cells arise from pre-existing cells.

  • Nucleus: Contains genetic material, structure detailed in Chapter 4.

  • Chromatin: Made of DNA and proteins, forms the chromosomes during cell division.

  • Nucleosomes: Bead-like structures formed by DNA wound around proteins, making up chromatin.

• Cell Division: Process in which a parent cell divides to form daughter cells.

Chromosomes and Sister Chromatids

• Chromosome: Each DNA molecule with its associated proteins. Each chromosome duplicates before division.

• Sister Chromatids: The two identical halves of a chromosome connected at the centromere, present just before cell division.

• Cell Cycle: Encompasses all events in a cell's lifetime, including:

  • Growth

  • Duplication of DNA

  • Nuclear division

  • Cytoplasmic division

Cancer Cells

• Cell Cycle Control System (CCCS): Regulates the cell cycle and consists of proteins that ensure proper timing and division of cells.

  • G1 Stage: Cells remain until they receive a signal to proceed.

  • G0 Stage: If no signal is received, cells may enter a resting state (e.g., nerve and some muscle cells).

  • Signal Reception: The CCCS proteins are influenced by the environment and signals from other cells.

What is Cancer?

• Definition: Cancer results from a malfunctioning CCCS, leading to uncontrolled cell division and tumor formation, categorized into:

  • Benign Tumors: Non-cancerous.

  • Malignant Tumors: Cancerous, with potential metastasis.

• Metastasis: Tumor cells can break off and spread, displacing healthy tissues.

• Types of Cancer:

  • Carcinoma: Affects skin and lining of the digestive tract.

  • Sarcoma: Cancer of bone and muscle.

  • Leukemia: Affects bone marrow.

  • Lymphoma: Affects lymph nodes.

• Treatment:

  • Radiation Therapy: High levels of radiation disrupt cell division.

  • Chemotherapy: Antimitotic drugs interfere with mitotic spindle formation, disrupting cell division.

Fertilization and Meiosis

• Fertilization: Union of gametes to form a zygote, which is diploid (2n).

  • Zygote in humans: 2n = 46 chromosomes.

  • Haploid Gametes: Each gamete contains half the number of chromosomes (n = 23).

• Mitosis and Development: Leads to multicellular diploid adults (2n = 46).

Variation in Species

• Independent Assortment of Chromosomes: The random segregation and assortment of chromosomes during gamete formation results in unique gametes.

  • Humans produce approximately 8 million types of gametes due to 2^23 combinations.

• Random Fertilization: Any one of the 8 million eggs can fertilize with any one of the 8 million sperms, leading to 64 trillion combinations for zygotes.

• Crossing Over: In Prophase I of meiosis, non-sister chromatids exchange segments, creating genetic diversity.

Errors in Meiosis

• Nondisjunction: Failure of sister chromatids or bivalents to separate correctly during meiosis.

  • This results in gametes with an abnormal number of chromosomes.

Down Syndrome (Trisomy 21)

• Occurs when there is an extra chromosome #21 in the zygote (total of 47 chromosomes).

• Characteristic features include developmental delays and physical traits associated with Down syndrome.

Sex Determination

• Male Gametes: Produce two types of sperm - X and Y.

• Female Gametes: Produce one type of egg - X.

• Outcome:

  • XX combination results in females.

  • XY combination results in males.

Non-disjunction of Sex Chromosomes

• XX Non-disjunction: Can result in an egg with two Xs or none.

• XX with Y: Non-disjunction can lead to conditions like Turner syndrome and Klinefelter syndrome.

Turner Syndrome (XO)

• Characteristics: A condition where females are short, infertile, and do not have functional ovaries.

Klinefelter’s Syndrome (XXY)

• Characteristics: Affects males who are taller than average, with small testes and infertility issues, and may exhibit mild mental impairment.

XYY Condition

• Affects males, typically taller than average with some academic challenges.

XXX (Triplo-x, 47XXX) Condition

• Affects females, characterized by developmental issues including lower IQ, learning difficulties, and taller stature than siblings.

Normal Karyotype

• Constitutes: 46 total chromosomes, organized into 23 pairs of homologous chromosomes.

  • 22 pairs are autosomes; the last pair determines sex (XX for females and XY for males).

• Karyotype Analysis: Can determine gender and chromosomal abnormalities.