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Reproduction (Meiosis (Meiosis II (separation of sister chromotids,…

- - - - homologous pairs of chromosomes are separated from each other . Homologues are chromosomes that are given the same number, but are of opposite paternal origin
        
        Prophase I - same as prophase of mitosis, except that homologues come together and intertwine in a process called synampsis
        
        Tetrad - the four chromatids after there is synapsis
        
        crossing over - when genetic material is exchanged from one chromatid with material from a chromatid in the homologous chromosome
        
        Mendel's second law of independent assortment - inheritance of one allele has no effect on the likelihood of inheriting certain alleles for other genes
        
        Metaphase I - homologous chromosomes line up on opposite side of the metaphase plate
        
        Anaphase I - homologous chromosomes are segregated to opposite poles of the cell. This accounts for Mendel's first law of segregation
        
        This is called disjunction - each chromosome of paternal origin disjoins from the homologue of maternal origin and either chromosome can end up in either daughter cell - thus the distribution of homologous chromosomes to the two intermediate daughter cells is random with respect to parental origin.
        
        Telophase I - the chromosomes may or may not fully decondense, and the cell may enter interkinesis (rest period during which chromosomes partially uncoil) after cytokinesis
      - homologous choromosomes - related chromosomes of opposite parental origin (one parental chromosome, one maternal chromosome)
      - Good diagram: https://www.khanacademy.org/science/biology/cellular-molecular-biology/meiosis/a/phases-of-meiosis
- - - - Seminiferous tubles
        
        F: Sperm is produced here and they are nourished by sertoli cells
      - Interstitial cells (of Leydig)
        
        F: secrete testostrone and other male sex hormones (androgens)
      - Located in the scrotum - the external pouch that hangs below the penis and maintains temp 2-4 degree lower than body
      - Sperm pathway
        
        Produced in seminiferous tubles
        
        passed to epididynis where their flagella gains motility
        
        During ejaculation the sperm passes through vas deferens
        
        and then to the ejaculatory ducts at the posterior edge of prostate gland
        
        two ejaculatory ducts fuse to form the urethra
      - What mixes with sperm?
        
        seminal fluid
        
        produced by seminal vesicles, prostate gland and bulbourethral gland
        
        Seminal vesicles contribute fructose to nourish sperm and give fluid slightly alkaline properties (helps with survival in acidic female body environmnet)
        
        prostate gland - give fluid mildly alkaline properties as well
        
        bulbourethral glands produce a clear viscous fluid that cleans out any remnants of urine and lubricates the urethra during sexual arousal
        
        combination of sperm and seminal fluid >>> semen
    - - Formation of haploid sperm through meiosis - occurs in seminiferous tubules
      - Diploid stem cell - spermatogonia
        
        After duplicating their genetic material (S stage) they develop into primary spermatocytes
        
        Meiosis I >>> secondary spermatocytes
        
        Meiosis II >>> spermatids
        
        Spermatogenisis results in four functional sperm for each spermatogonium
    - - Head
        
        Contains the genetic material
        
        Sperm head is covered by acrosome - good for penetration of ovum
        
        Derived from the Golgi apparatus
      - Midpieace
        
        Filled with mitochondria and it generates the ATP from fructose so that it can swim through the female body
      - Flagellum
        
        For motility
- - - - G1 - Presynthetic gap
        
        Create organelles for energy and protein production (mitochondria, ribosomes, endoplasmic reticulum)
        
        Increase their size
        
        Restriction point - governs passage to the next stage (S-synthesis)
        
        Criteria 1: containing the proper complement of DNA
      - S - Synthesis of DNA
        
        Cell replicates its genetic mtrl so that each daughter cell will have identical copies
        
        After replication - chromosome consists of two identical chromatids, bound together in a specialized region known as centromere
        
        Humans at this stage still have 46 chromosomes, eventhough 92 chromatids are present
        
        Note: each chromatid is composed of a complete double stranded molecule of DNA - sister chromatids are identical copies of each other. Chromosome maybe used to refer to a single chromatid before S phase or the pair of chromatids attached at the centromere after S phase
      - G2 - Postsynthetic gap
        
        The cell passes through another check
        
        DNA has already been replicated
        
        Cell checks to make sure there are enough organells and cytoplasm to divide between the two daughter cells
        
        The cell checks that DNA replication proceeded correctly to avoid passing on an error to daughter cells
      - M- Mitosis
        
        Mitosis and cytokinesis happen at the same time
        
        Mitosis
        
        prophase, metaphas, anaphase and telophase
        
        Cytokinesis
        
        splitting cytoplasm and organelles into two daugther cells
    - - individual chromosomes are not visible under light microscopy - lless condensed form know as chromatin - the DNA has to be available for RNA polymerase so that genes can be transcribed
      - During mitosis -DNA are tightly coild to avoid losing of genetic material
  - - - G1/S point where the goal is to make sure that the DNA is not damaged and is ready to be replicated - main protein in control of this is known as p53.
    - - G2/M check point - make sure that the cell has acheived adequate size and the organelles to support the daughter cells - p53 does play a role in this again
    - - CDK will be only activated when it is matched with the right cyclin - the pairing creates a CDK-cyclin complex which then phosphorylate transcription factors
        
        Transcription factor - promote transcription of fenes required for the next stage of the cell cycle
    - - Tumors
        
        when the cell is being produced without a regard for damanged cell
      - Metastasis
        
        when the cell produces factors such as proteases that can digest basement membrane or factors that encourage blood vessel formation the damanged cell travels to other parts of body -- this can lead to spread of cancer
      - When the cell cycle control becomes deranged, damaged cells go under mitosis and this may lead to cancer
      - Most common mutation - is mutation of a gene that produces p53. It is called TP53. This causes the cell production to not stop when the cell is damaged --
      - Cancer causing genes
        
        oncogenes - genes that when mutated, actively promote cell division
        
        tumor suppressor genes - genes that when mutated, lose their ability to regulate or pause the cell cyle
  - - - Chromatin condenses into chromosomes
      - Centriole pairs separate and move toward opposite poles of the cell
        
        They are located outside of the nucleus in a region known as centrosome
        
        F: correct division of DNA
      - Once centriole pairs move towards the opposite sides of the cell they form spindle fibers (they are made of microtubules)
        
        they are one of the two microtible organizing centers
        
        other microtuble organizing center: basal body of flagellum or cilum
        
        some microtubles form asters - that anchor the centrioles to the cell membrane
        
        others extend toward the middle of the cell
      - Nuclear membrane dissolves during prophase -- allowing these spindle fibers to contact the chromosomes
      - Nucleoli become less distinct and may disappear completely
      - Kinetochores appear at the centromere
        
        kintetochore are protein structures located on the centromere
        
        F: attachement point for specific fibers of the spindle appratus (kinetochore fibers)
    - - Align chromosomes at the metaphase plate (equatorial plate) - equidistant between the two poles of the cell
        
        the kinetochore fibers interact with the fibers of the spindle appparatus to align the chromosomes
    - - sister chromatids separate and each of them have its own centromere -
      - this happens by shortening o f the kinetochore fibers
    - - Reverse of prophase
        
        Spindle appratus disappears
        
        Nuclear membrane reforms around each set of chromosomes
        
        Nucleoli reapprear
        
        Chromosomes uncoil, resuming the interphase form
        
        Cytokinesis happens at the end of telophase
        
        Cells go through 20-50 division before a programmed death