Genetics lab one

• Interphase: The first phase of the cell cycle, during which the cell grows and copies its DNA. includes the interval between divisions.
• Mitotic (M) phase: nuclear material is organized and divided
• Interphase is sub divided into:

  S-phase: synthesis of DNA occurs prior to cell entering mitosis.

  G1 & G2 (gap 1 and gap 2): periods of metabolic activity, growth and differentiation.
• Stages of mitosis: Prophase, Prometaphase, Metaphase, Anaphase, Telophase, and cytokineses
• Prophase: migration of centrioles to opposite ends of cell. Nuclear envelope breaks down. Chromatin condeses.
• Sister chromatid: two genetically identical parts of each chromosome formed from single replicative event during S-phase.
• centrioles: 2 microtubules that form a ring around the cell
• Prometaphase: period of chromosome movement
• Metaphase: Chromosomes line up along the middle of the cell. (metaphase plate)
• Kinetochore: multilayered plates of proteins associated with centromere.
• Centromere: A region of a chromosome where the two chromatids are attached.
• anaphase: sister chromatids separate and are pulled to opposite ends of cell.
• Disjunction (anaphase): sister chromatids of each chromosome are separated from each other. Shugosin is degraded. Separase removes remaining cohesion at centromere.
• Daughter chromosomes : migrating chromatids
• Telophase: Chromosomes uncoil and decondense. Nuclear envelope reforms. Spindle fibers disappear. Nucleolus reforms.
• Cytokinesis: division or partitioning of the cytoplasm.
• Prophase 1: chromatin starts to condense into visible chromosomes. Homology search begins. Homologous chromosomes undergo initial alignment, referred to as rough pairing. Paired Homology referred to as bivalents. homologous pairs of chromosomes undergo synapsis.
• tetrad: the two pairs of sister chromatids between paired homologous chromosomes
• Crossing over: occurs between chromatids of synapsed homologs.
• Chiasma: now visible in prophase 1. These are the locations where non-sister chromatids have undergone crossing over.
• Prophase 1 additional: nuclear envelope and nucleolus break down. Spindle fibers are attatched to centromeres of each tetras.
• Metaphase 1: terminal chiasmmats are still visible. Spindle fibers move each tetrad to metaphase plate. Alignment along plate is random.
• Anaphase 1: Cohesion degraded between sister chromatids. Dyads pulled toward each pole. Disjunction in this case is the separation of homologous chromosomes.
• Telophase 1: some organisms have nuclear membrane reform, followed by short interphase period. Some other organisms proceed directly from anaphase 1 to meiosis 2. No replication!
• Prophase 2: dyads composed of 1 pair of sister chromatids.
• Metaphase 2: centromeres positioned on equatorial plate. Shugosin complex degraded. Centromeres separate.
• Anaphase 2: Sister chromatids separate and move to opposite poles of the cell
• Telophase 2: each chromosome is present as a monad. Cytokinesis results in 4 haploid gametes.
• Onion cell divisions

  
• The first meiotic division: Prophase 1, metaphase 1, anaphase 1, telophase 1
• The second meiotic division: prophase 2, metaphase 2, anaphase 2, telophase 2