Mitosis vs. Meiosis, Heredity & DNA

Mitosis vs. Meiosis: Cell Division

Key Differences

• Purpose:
  • Mitosis: Makes body (somatic) cells.
  • Meiosis: Makes sex (gamete) cells - sperm/egg.
• Result:
  • Mitosis: 2 identical diploid cells (2n).
  • Meiosis: 4 unique haploid cells (n).
• Use:
  • Mitosis: Growth, repair.
  • Meiosis: Reproduction.
• Rounds of Division:
  • Mitosis: 1.
  • Meiosis: 2 (Meiosis I & II).

Tips

• Mitosis = Maintenance (for body cells).
• Meiosis = Making eggs/sperm.

Starting Point: Diploid Cells (2n)

• Humans start with 46 chromosomes (23 from mom + 23 from dad).
• Before division, chromosomes duplicate but are still counted as 46 (because the sister chromatids are joined).

Stages of Cell Division: PMAT

• Use P.M.A.T. to remember the stages:
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

Mitosis

1. Prophase: Chromosomes condense (visible & thick).
2. Metaphase: Chromosomes line up in the middle (single file).
   • Mnemonic: "M = Middle"
3. Anaphase: Sister chromatids pulled away to opposite sides.
   • Mnemonic: "A = Away"
4. Telophase: New nuclei form. Cell starts to split.
5. Cytokinesis: Cell fully splits into 2 identical diploid cells.

Meiosis

• Happens in 2 parts:
  • Meiosis I - separates homologous chromosomes:
    • Prophase I: Chromosomes pair with homologous partners → crossing over happens → genetic diversity!
    • Metaphase I: Pairs of chromosomes line up in the middle.
    • Anaphase I: Entire chromosomes pulled apart (not chromatids yet).
    • Telophase I + Cytokinesis: 2 cells form.
  • Meiosis II - separates sister chromatids (like mitosis):
    • Prophase II: Chromosomes condense again (no crossing over).
    • Metaphase II: Chromosomes line up single file.
    • Anaphase II: Chromatids pulled apart.
    • Telophase II + Cytokinesis: Total of 4 haploid cells created.

Tip

• Meiosis = More stages, More diversity, Half the DNA

Heredity & DNA

What is Heredity?

• Traits are passed from parents to offspring.
• Influenced by:
  • Genes (DNA)
  • Environment (e.g., nutrition)

DNA Structure

Memory Tricks

Base pairs:

• A = T "Apples in the Tree”
• C = G → "Cars in the Garage"

RNA vs DNA

• RNA Base Tip:
  • A = U (Apples Under the tree)
  • C = G (Same as DNA)

Types of RNA

From DNA to Protein: Protein Synthesis

Step 1: Transcription (DNA → mRNA)

• Happens in the nucleus
• Enzyme: RNA Polymerase
• DNA → mRNA strand (complementary bases)

Tip:

Transcription = "Copying the code"

C comes before L in alphabet → Transcription before Translation

Step 2: Translation (mRNA → Protein)

• Happens at ribosomes in the cytoplasm
• mRNA read in codons (3 bases = 1 amino acid)
• tRNA brings matching amino acid using an anticodon
• Amino acids link into a polypeptide chain → Protein!
• STOP codons: signal the end of protein building

Genes & Chromosomes

• A gene = section of DNA coding for a protein
• A chromosome = tightly wound DNA around proteins (histones)
• Humans have 46 chromosomes in body cells (23 pairs)
• Gametes (sperm/egg) have 23 chromosomes

Regulatory vs. Structural Genes

Practice Question Review

1. During which phase does crossing over occur?
   • Prophase I
2. Difference in genetic outcome between mitosis and meiosis?
   • Mitosis: 2 identical diploid cells
   • Meiosis: 4 unique haploid cells
3. Why is Anaphase I important in meiosis?
   • It creates genetic diversity by randomly separating chromosomes.
4. Relationship between DNA, genes, and chromosomes?
   • Chromosomes = DNA, and genes = DNA segments that code for traits.
5. Role of regulatory genes?
   • Control the expression of other genes (on/off switch).
6. What starts transcription?
   • RNA Polymerase
7. Role of mRNA?
   • Template for building proteins