cell divison

1. Chromosomes

• Chromosomes vs. Sister Chromatids vs. Homologous Chromosomes

Chromosomes: Carries genetic information

Sister Chromatids: two identical copies of one chromosome joined at centromere

Homologous Chromosomes: Twin chromosomes (contains genes from both parents). Have same structure (length, shape) and same gene sequence (same genes in same order), but may have different forms of the traits they code for.

• Karyotype: Image of a cell’s chromosomes arranged by size, shape, and centromere location

• Autosomes vs. Sex chromosomes

Autosomes: Non-sex chromosomes (does not define gender)

Sex Chromosomes: Define gender

• Diploid vs. Haploid

Diploid: 2n = 46 chromosomes (applies to human somatic (body) cells). Two of each type of chromosome.

Haploid: n = 23 chromosomes (applies to gametes → egg/sperm). One of each type of chromosome.

• Relationship between somatic cells and gametes in terms of chromosome number

Somatic cells are diploid, 2n = 46 chromosomes

Gametes are haploids, n = 23 chromosomes

• Formulas for representing chromosome number and calculating possible chromosome combinations in gametes

2n = Diploid, contains 2 sets of chromosomes (23 chromosomes each, 46 in total)

n = Haploid, contains 1 set of chromosomes (23 chromosomes in total)

2. The Cell Cycle and Mitosis

• Order of steps in the cell cycle

Interphase, prophase, metaphase, anaphase, telophase, cytokinesis

• Events that occur during each stage of the cell cycle/mitosis

Interphase: 

• G₁ → increases proteins, organelles, and size

• S → duplicates chromosomes (DNA replication)

• G₂ → growth and error check

• (G₀ → cell no longer divides)

Prophase: Chromosomes condense, spindle forms, nuclear envelope breaks down, sister chromatids attach to spindle

Metaphase: chromosomes line up at the center of the cell

Anaphase: sister chromatids are pulled to opposite sides of the cell by the spindle fibers

Telophase / Cytokinesis: spindle disappears, two nuclear membranes form, chromsomes uncoil, cell’s cytoplasm splits

• Purpose of cell cycle checkpoints

Makes sure key events such as DNA replication and cell division occur properly (if a cell misses a step, checkpoints allow it to redo to meet the requirement or kills the cell)

Cyclins: proteins that allow checkpoints and regulated cell division

• Cancer

Uncontrolled cell division occurs when a tumor disrupts body tissues

• Uncontrolled cell division

• Skip interphase and go straight to mitosis

• Reproduce at a high rate

• create tumors

• benign tumors are a mass of cells

• malignant tumors (mass of cancerous cells) may take a lifetime of mutations to occur, abnormal growth, altered cytoplasm and membrane, metastasis spreads throughout the body

3. Meiosis

• Spermatogenesis vs. oogenesis

Spermatogenesis: Formation or development of sperm, happens throughout lifetime, all 4 haploid cells are used

Oogenesis: Development of mature oocytes (eggs), immature eggs do not complete development until many years later (ends at a certain age), only one haploid cell is used

• Events that occur during each stage of meiosis

Interphase - DNA replication, G₁, S, & G₂

Prophase I - The nuclear envelope breaks down, tetrads form (two homologous chromosomes), and spindles form.

Metaphase I - The homologous chromosomes line up in the middle of the spindle fiber.

Anaphase I - The spindle fibers pull the sister chromatids to opposite sides of the cell.

Telophase I - Cytoplasm splits into two daughter cells (haploid) and now there are 2 pairs of homologous chromosomes.

Prophase II - Nuclear membrane forms on both cells.

Metaphase II - The chromosomes line up at the center on both the cells.

Anaphase II - The sister chromatids split up to opposite sides of the cell.

Telophase II - Cytoplasm splits for both cells and 4 pairs of haploid daughter cells are made.

• Major differences between meiosis I and meiosis II

Meiosis I is like mitosis (PMAT) that produces two haploid cells, and splits homologous chromosomes

Meiosis II creates 4 haploid cells, and splits sister chromatids

• How Meiosis Introduces Variations in Traits

Crossing over in prophase I: When homologous chromosomes come together to form tetrads, the arms of the chromatids overlap, which creates many more possibilities for genetic variation of the gametes.

Segregation of chromosomes into gametes: During formation of gametes, homologous chromosomes (pairs of chromosomes, one from each parent) separate, ensuring each gamete receives only one copy of each chromosome, and one allele for each gene. 

Random fertilization: During sexual reproduction, the male gamete and female gamete that fuse to produce an offspring are selected randomly from the pool of male and female gametes. (determines gender)

4. Comparing Mitosis and Meiosis

Determine whether the following characteristics apply to mitosis, meiosis or both by putting and “X” in the appropriate column(s).

5. Chromosomal mutations

• Types of changes in chromosome structure

Duplication: Repeated section of a chromosome

Deletion: A section of a chromosome that is lost or deleted

Insertion: a segment of DNA that can move spontaneously within or between chromosomes; can result in an insertion

Inversion: Broken pieces of chromosomes that become reattached backwards

Translocation: Broken pieces of chromosomes that gets attached to a different area (may be the same chromosome or different)

• Types of changes in chromosome number

  • Polyploidy vs. Aneuploidy

Polyploidy: Having three or more of each type of chromosome

Aneuploidy: Having too many or too few copies of the same chromosome

• Nondisjunction

When sister chromatids or homologous chromosomes fail to separate during nuclear division