bio L6

• Haploid cells


  Have 1 set of chromosomes
• Diploid cells

  Have 2 sets of chromosomes
• Mitosis

  1. Prophase

  2. Prometaphase

  3. Metaphase

  4. Anaphase

  5. Telophase

  6. Cytokinesis
• Chromosomes


  Highly condensed DNA, usually made up of 1 chromatid
• Homologous chromosomes


  Two pieces of DNA within a diploid organism which carry the same genes, one from each parental source
• Sister chromatids


  The two chromatids that form after DNA replication
• Humans have 23 pairs of chromosomes (46 chromosomes) in each somatic cell
• Ploidy number


  The number of complete sets of chromosomes
• DNA content


  The amount of DNA in the cells
• Human somatic cells are diploid (2n) and have 2c DNA content
• Gametes are haploid (n) but have 2c DNA content initially, which increases to 4c during cell division
• Cell division is needed for growth, healing/tissue repair, and reproduction in multicellular organisms
• Main cell types in sexually reproducing organisms

  • Somatic cells
  • Germ cells
• Somatic cells

  Give rise to every other cell type, except the sperm and egg cells (gametes)
• Germ cells

  Give rise to the gametes (sex cells) of an organism that reproduces sexually: Sperm and egg cells
• Somatic cells are diploid


  Germ cells are diploid at the start but develop to haploid cells (gametes) during development
• Interphase


  1. G1 phase

  2. S phase

  3. G2 phase
• G1 phase


  Cell enlarges and organelles start duplicating
• S phase

  DNA replication occurs, increasing DNA content from 2c to 4c
• G2 phase


  Final cell growth, replenishing energy and synthesizing proteins necessary for chromosome manipulation, organelle duplication, and cytoskeleton dismantling
• Mitosis

  Cell division process in somatic and primordial germline cells, producing two new cells genetically identical to the original
• The two daughter cells formed after mitosis can enter the cell cycle again if more cells are required by the body
• Meiosis I

  1. Prophase I

  2. Metaphase I

  3. Anaphase I

  4. Telophase I and cytokinesis
• Meiosis II


  1. Prophase II

  2. Prometaphase II

  3. Metaphase II

  4. Anaphase II

  5. Telophase II

  6. Cytokinesis II
• Meiosis


  • Occurs only in primary germ cells
  • Cell divides to produce four new cells genetically non-identical to the original
  • Involves meiosis plus cytokinesis
  • Used for production of gametes and to reduce chromosome number and generate genetic variation
• Mitosis is a tightly controlled process but errors can occur to the DNA at any phase
• Changes/damages to DNA may be harmless or it can lead to development of diseases such as onset of cancer
• Damage to DNA can be caused by environmental factors, random changes within the cell during the process of DNA replication or mitosis, which may lead to changes in the DNA sequence
• For errors that happen during mitosis, only the daughter cells derived from the affected parental cell will have the alteration
• Errors that occur in somatic cells during mitosis will not be passed on to offspring
• Possible errors during mitosis

  • Errors during DNA replication
  • Errors during mitosis process
• Possible errors during meiosis

  • Errors during DNA replication
  • Errors during recombination
  • Errors when the chromosomes segregate to the daughter cells (Meiosis I and II)
• If an error occurs in an egg or sperm, the person made from that gamete will have the change in every cell of their body
• Changes that occur in germ cells during meiosis will be passed on to offspring
• Alterations which disrupt gene function and lead to disease are known as mutations
• If chromosomes of the same pair misalign during meiosis, the exchange of material may result in duplications (extra genetic material) or deletions (missing genetic material)
• During crossing over or recombination in meiosis, small pieces of chromosomes may get removed, inverted or switched to a completely different sequence
• Nondisjunction is when the homologous chromosomes fail to separate during meiosis, resulting in trisomy (an extra chromosome of a particular pair) or monosomy (one chromosome fewer in each cell)