Week 4

• Mitosis: Repairs + produces body cells

  • Makes IDENTICAL cells replacing what was lost

  • Interphase: Growth, DNA replication + cell functions (MITOSIS is a SHORT part (10%) of the cell cycle whereases INTERPHASE is 90%)

• e.g. when chromosomes replicate, it is still counted as ONE chromosome, but just with TWO chromatids (to ensure that DNA is still intact and doesn't lose itself as it gets duplicated)

• Mitosis steps of division (REFER BACK TO AMEBOA SIS VID + RESEARCH):

  1. Prophase:

  • Condensing (Prior to this, it would be big loops of DNA hanging in the interphase)

  • Chromosomes are thickening + VISIBLE --> chromatin condenses into chromosomes (nucleolus disappears)

  • Spindle fibres (RESEARCH + REFER TO VID)

  1. Metaphase:

• M for MIDDLE

• Chromosomes line up in MIDDLE of cell --> nucleus is no longer their (disassembled)

• Nucleus starting to dissolve

• Spindle fibres attach to the middle and to the sides of the individual chromatids

  2. Anaphase:

• A for AWAY --> Chromatids move AWAY (moving towards opposite sides)

  • CHROMOTIDS (use chromatids once the chromosomes have been separated) are being pulled away to separate them fully

  3. Telophase:

• Chromatids form together on each ends

• Nuclei surrounds the chromatids on both sides --> nuclei membrane reforms

  4. Cytokinesis

• Splits the cytoplasm and finishes the replication/dividing process (mitosis)

Starter:

Distinguish between the terms:

• Chromosomes --> Come from parents (23 from each side); storage units for DNA

• Sister chromatids --> Forms an x (occurs after DNA replication --> same info on each of them; not sister chromatids if it is another separate chromatid because they have different DNA info)

• Homologous chromosomes: Same length, same gees

• Alleles: An alternative form of a gene (different DNA)

Starter:

Distinguish between the terms:

• Chromosomes --> Come from parents (23 from each side); storage units for DNA

• Sister chromatids --> Forms an x (occurs after DNA replication --> same info on each of them; not sister chromatids if it is another separate chromatid because they have different DNA info)

• Homologous chromosomes: Same length, same gees

• Alleles: An alternative form of a gene (different DNA)

Meiosis:

• Type of cell division which occurs in the germ line cells (ovaries and testes) to produce gametes (sperm + egg cells/non-genetically identical)

• Produces cells that are haploid (diploid (2n) = 46 chromosomes, haploid (n) = half the number of normal chromosomes SO, haploid = 23 chromosomes)

• Purpose: Helps with sexual reproduction to create genetic variation

• Creates four genetically unidentical gametes from another

Amoeba sister's video notes:

• Meiosis = reduction division --> starts with starting cell (could be primary spermatocyte or primary oocyte ) with 46 chromosomes --> ending cell only has 23 chromosomes

• Interphase happens before the meiosis occurs (growth, DNA replication, cell functions)

• Because you have to divide TWICE, you have to undergo PMAT x 2 --> since it is going from 46 chromosomes (92 chromatids), to 23 chromosomes (46 chromatids), to 23 chromosomes (23 chromatids)

  • Prophase 1 (BEFORE: comes before all the other processes start)

    • Thicken

    • Lines up with their homologous pairs (same types of genes in same location)

    • Crosses over --> when chromosomes in pairs find a way to transfer to genetic information to each other (recombinant chromosomes)

  • Metaphase 1:

    • Chromosomes move to middle of the cell

    • Chromosomes are in PAIRS in the middle, not by ITSELF

  • Anaphase 1:

    • CHROMSOMES pulled to each side by spindle fibres

  • Telophase 1:

    • Two newly formed nuclei --> becomes obvious that meiosis is going to end with two new cells

    • Cytokinesis splits it into two new cells

  • Prophase 2:

    • Chromosomes and spindles become to form

    • NO MORE crossing over/homologous pairing

  • Metaphase 2:

    • Recombinant chromosomes are in SINGLE FILE line, not in pairs anymore

  • Anaphase 2:

    • CHROMOTIDS are pulled away from spindle fibres instead

  • Telophase 2:

    • Nuclei reforms

    • The two cells before are divided --> results in FOUR cells

    • Cytokinesis follows to COMPLETELY SPLIT the cytoplasm

• AS A RESULT, this process leads to genetically different info/NO CELL IS IDENTICAL (explains why siblings look different e.g.)