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Topic 3 (Sexual Reproduction (Inheritance (Chromosomes (sex chromosomes #,…

- - - - adaptions
        
        flagellum tail
        
        motility to move through the cervix and uterus to reach the ovum to fertilise it in the Fallopian tube
        
        acrosome
        
        releases digestive enzymes which break down the jelly-like coating of the ovum enabling the sperm to penetrate it
        
        lots of mitochondria in midpiece
        
        respiration to provides ATP for movement of flagellum
    - - adaptions
        
        zona pellucida
        & follicle cells
        
        protective coating & cortical granules cause zona pellucida to thicken after the first sperm penetrates, preventing entry of other sperm
        
        cytoplasm contains protein and lipid reserves for early development of embryo
  - - - Sperm deposited high up in the female vagina, close to entrance of cervix
      - Sperm then make their way up through cervix and uterus to an egg cell in oviduct
      - Sperm makes contact with zona pellicuda of ovum → triggers acrosome reaction
        
        (acrosome swells & fuses with sperm surface membrane to release enzymes – exocytosis)
      - Digestive enzymes digest follicle cells & zona pellicuda, allowing sperm through membrane
      - Sperm head fuses with ovum cell membrane → triggers cortical reaction
        
        (egg cell releases contents of cortical granules (vesicles) into space between cell membrane & zona pellicuda)
      - Chemicals make zona pellicuda thicken, making it impenetrable to other sperm
      - Sperm nucleus enters ovum & tail is discarded (only nucleus enters ovum)
      - Nucleus of sperm fuses with nucleus of ovum (fertilisation) = zygote
  - - - male = anther
        
        produces pollen
      - female = ovary
        
        produces ovules
    - - male = testes
        
        produces spermatozoa
      - female = ovaries
        
        produces ova
  - - - sex linkage
        
        males only have 1 X chromosome → often only have 1 allele for sex-linked genes → expressed even if it’s recessive (no dominant to overpower) → more likely to show recessive phenotypes for sex-linked genes
    - - sex chromosomes #
        
        male = XY
        
        female = XX
        
        1 pair
      - autosomes
        
        22 pairs
      - 23 homologous pairs
        
        1 maternal
        
        1 paternal
    - - e.g. flower colour
      - phonotype is blend of the dominant & recessive alleles
    - - e.g. blood group
      - both alleles are fully expressed
- - - - magnification: up to x1500
      - resolution: 200nm / 0.2μm
      - uses light (longer wavelength)
      - colour images
      - can view live specimens
    - - Transmission electron microscope (TEM)
        
        focuses beam of electrons through (thin) specimen
        
        high quality images
      - Scanning electron microscope (SEM)
        
        scans beam of electrons across specimen which are reflected off its surface
        
        3D images
      - requires use of a vacuum (dead cells only)
      - black & white images
      - stain required
      - uses electrons (shorter wavelength)
      - magnification: up to ×500,000
      - resolution: 0.1nm
- - - - repairing damaged tissue
      - replacing worn out cells
      - asexual reproduction (bacteria, hydra, fungi & some plants)
      - growth of multicellular organisms
    - - Metaphase
        
        chromosomes (each with 2 chromatids) line up along the middle of the cell and become attached to the spindle by their centromere
      - Anaphase
        
        centromeres divide, separating each pair of sister chromatids
        
        spindles contract, pulling chromatids to opposite poles (ends) of the spindle, centromere first (makes chromatids appear v-shaped)
      - Prophase
        
        chromosomes condense, getting shorter and fatter, visible as two strands (chromatids)
        
        2 identical (apart from mutations) strands joined by centromere
        
        centrioles move to opposite poles of the cell, forming spindle
        
        nuclear envelope breaks down and chromosomes lie free in the cytoplasm
      - Telophase
        
        chromatids reach opposite poles on spindle & spindle fibres break down
        
        nuclear envelope forms around each group of chromosomes, so there are now 2 nuclei
        
        chromosomes uncoil, become long and thin again (no longer visible under microscope)
    - - no. of cells with visible chromosomes / total no. of cells observed
  - - - Gap 1 phase
        
         protein and organelle synthesis occurs (cellular contents excluding chromosomes) causing cell to double in size
      - Synthesis phase
        
         semi-conservative replication produces an identical copy of each of the 46 chromosomes
        
         centrosome is also duplicated (helps separate DNA during mitosis phase)
      - Gap 2 phase
        
         cell synthesises more proteins and organelles
        
        preparation & organisation of contents ready for mitosis
        
        cell checks for & repairs any errors in DNA replication
      - Mitosis
      - Cytokenesis
        
        cytoplasm divides = 2 daughter cells that are genetically identical to the original cell and to each other
        
        animal cells: starts from the outside, with the membrane
        
        plant cells: cell plate first forms to slit the cell in two, and cell membrane and wall material is laid out along this plate
  - - - 1) DNA replicates
      - 2) DNA forms double armed chromosomes made from 2 sister chromatids
      - 3) Chromosomes arrange into homologous pairs
      - 4) 1st division
      - 5) 2nd
        division
    - - creating haploid cells
        
        needed so that when 2 gametes fuse to produce cell with correct no. of chromosomes
      - creating genetic variation
        
        crossing over
        
        chromatids cross (at chiasmata), break off original chromatid, swap and re-join to other chromatid
        
        independent assortment
        
        chromosomes in daughter cells are randomly assorted depending on allignment of chromosomes during 1st division of meiosis
- - - - Methylation of DNA
        
        transcription proteins/enzymes can’t bond to gene, so gene is not expressed
        
        a methyl group (-CH3) is attached to DNA at CpG site (where a C & G are next to each other)
      - Acetylation of histones
        
        acetyl groups (-COCH3) are added to histones, chromatin is less condensed
        
        transcription proteins/enzymes can bind to DNA, allowing genes to be transcribed
      - De-acetylation of histones
        
        transcription proteins/enzymes can’t bind to DNA, so genes aren’t transcribed
        
        acetyl groups (-COCH3) are removed from histones → chromatin becomes highly condensed
      - epigenetic changes can be passed on after cell division
      - epigenome = all of the chemical compounds that have been added to the genome as a way to regulate the expression of all the genes within the genome
      - Lac operon
        in E. coli
        
        when lactose is present
        
         lactose binds to repressor, changing its shape
        
         repressor can’t bind to operator site
        
         RNA polymerase can begin transcription
        
         β-galactosidase is produced which breaks down lactose to be respired
        
        when lactose
        is not present
        
        regulatory gene (lacl) produces lac repressor
        
        lac repressor binds to operator site
        
        RNA polymerase can’t bind to promotor region
        
        transcription of mRNA for β-galactosidase is blocked
  - - - tend to be polygenic
      - environment factors + genotype
    - - tend to be monogenic
- - - - mitochondria
      - centrioles
      - cell membrane
      - lysozymes
      - smooth ER
      - rough ER
      - golgi apparatus
      - nucleus
      - ribosomes
      - cytoplasm
    - - movement of proteins in protein synthesis
        
        1) Transcription of DNA to mRNA
        
        2) mRNA leaves nucleus through nuclear pore
        
        3) Polypeptide chains synthesised from amino acids on ribosomes
        
        4) Protein enters & moves through RER assuming 3D shape en route
        
        5) Vesicles pinched off the RER contain the protein
        
        6) Vesicles from RER fuse to form the flattened sacs of the Golgi apparatus
        
        7) Proteins are modified within the Golgi apparatus
        
        8) Secretory vesicles pinched off the Golgi apparatus contain the modified protein
        
        9) Vesicle fuses with cell surface membrane, releasing protein (exocytosis)
  - - - nucleoid
      - plasmids
      - cell wall
      - pili
      - cell membrane
      - flagella
      - slime capsule
      - mesosomes
- - - - can differentiate to produce all cell types (including embryonic cells)
      - all meristems (plant stem cells) are pluripotent
    - - can differentiate to produce all specialised cells except embryonic
  - - - 1) Adult stem cell is removed from the body and the nucleus is placed inside an empty ovum creating a new pre-embryo cell containing patient DNA
      - 2) A mild electric shock is used to trigger the development of the embryo producing a collection of embryonic stem cells with the same genetic information as the patient
      - 3) The stem cells are removed from embryo & cultured to grow into required tissue/organ which is then transplanted into patient
    - - adult tissue
        
        (mesenchymal)
      - embryos
    - - can potentially help treat a range of medical problems – improve quality of life
      - new limbs/organs could be grown
        from stem cells
      - will help scientists to learn about human growth and cell development
      - adult stem cells can be used (not a potential life) & won’t be rejected (if from same person)
      - cells could be used in drug testing
    - - destruction of viable blastocysts
      - immunosuppressant drugs often needed after transplant which makes the body vulnerable to other infections
      -  possibility of rejection (different antigens)
      - blood cells formed from donor's stem cells sometimes attack patient’s cells
      - new technology – long term effects unknown
      - most adult stem cells is that they are pre-specialized