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.

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

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.

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: 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).

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.

Nondisjunction: Failure of sister chromatids or bivalents to separate correctly during meiosis.
- This results in gametes with an abnormal number of chromosomes.

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.

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.

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.

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

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

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

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.