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Topic 3 - Genetics (Genetic modification and biotechnology (Gene transfer…

- - - - GM Crops Risks
        
        plants that are modified to have toxins that naturally kill pests can causes resistance in the pests, leading to same original problem
        
        can have unexpected adverse effects on other species
        
        weeds can become herbicide resistant through cross pollination
        
        effects on human body are not entirely known
  - - - Many plant species and some animal species have natural methods of cloning
        
        Plants use a variety of natural methods of cloning involving stems, roots, leaves or bulbs.
        Garlic bulbs are modified plant leaves. All the bulbs in the group are genetically identical to each other.
        Strawberry plants grow horizontal stems called runners that grow roots into the soil. These small plants develop into independent cloned strawberry plants
      - Animals
        At the very early embryo stage, cells are still pluripotent (meaning they can become any type of tissue)
        These cells can be separated artificially in a laboratory in order to create more than one of the same organism
        The separated pluripotent cells can then be inserted into the uterus of a surrogate mother or mothers in order to produce genetically identical offspring
        The separation of cells has to happen early in development, preferably the 8 cell stage
        This ability was first discovered by trying on Sea anemones
      - Methods have been developed for cloning adult animals using differentiated cells
        
        Once cells start to differentiate and embryos develop into a fetus and eventually, an adult cloning becomes much more difficult
        Therapeutic cloning is an example of cloning using differentiated cells
        This type of cloning can be used to create a specific tissue or organ
        Cloning using differentiated cells can also be used to reproduce organisms like Dolly the sheep. This is done through somatic-cell nuclear transfer.
      - Method used to create Dolly (first cloned sheep)
        
        Somatic cell removed from the donor and cultured (removed from the udder in Dolly).
        An unfertilized egg is removed from another sheep and its nucleus is removed.
        The unfertilized egg is fused with the cultured somatic cell from the first sheep using an electric current.
        The embryo created now contains all the genetic information from only the first sheep.
        The embryo divides by mitosis “in vitro” until it reaches the blastocyst stage(hollow ball of about 16 cells).
        Next, the blastocyst is transferred and embedded into the womb of a third surrogate sheep.
        The cloned embryo will continue to grow until a baby lamb is born that is genetically identical to the first sheep that donated the somatic cell.
- - - - Haploid nuclei have one copy of each chromosome or one full set of the chromosomes in that particular species eg. Human 23 chromosomes
        
        These are called gametes, which are sperm and egg
        
        Human sperm and eggs each contain 23 chromosomes
  - - - A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
        
        In karyotyping, chromosomes are arranged in pairs according to their size and structure with the largest at chromosome pair 1 and the smallest at chromosome 22.
        
        Chromosomes are stained during mitosis (generally in metaphase) in order to see the chromosomes, and a micrograph is taken of the stained chromosomes
        
        This stained image of the chromosomes is called a Karyogram
        The 23rd pair is the sex chromosomes. Females have two X chromosomes and males have one X chromosome and one Y chromosome.
- - - - Huntingtons Disease
        Humans have two copies of the Huntingtin gene (HTT), which codes for the protein Huntingtin (Htt)
        Huntington’s disease is dominantly inherited. Meaning only one bad copy of the gene from either the mother or father will result in Huntington’s disease.
        Therefore, children of people affected with the disease have a 50% chance of getting that allele from an affected parent.
        If both parents have Huntington’s disease, offspring have a 75% chance of being affected by the disease.
        Huntington's disease is a neurodegenerative genetic disorder that affects muscle coordination and leads to mental decline and behavioral symptoms
        In Huntington’s disease, a repetition of a CAG sequence in the gene encoding for the protein Huntingtin makes it clump together in our brain cells, ultimately making the brain cell die.
        The exact mechanism of the disease is still being researched; however, this is what is current research suggests.
        The repetitive glutamates (CAG) in the Huntington protein change the shape of the brain cells, affecting their function. The glutamate sends signals that constantly over-excite brain cells. Their overexcitement leads to cell damage, and ultimately cell death.
    - - Red-Green Colour Blindness and haemophilia
        Color blindness and hemophilia are both examples of sex linkage.
        Color blindness and hemophilia are produced by a recessive sex-linked allele on the X chromosome.
        X-linked recessive diseases such as color blindness and hemophilia are more common in males because males only carry one X chromosome, therefore if they inherit the X chromosome with the disease, they will have the disease.
        On the other hand, since females have two X chromosomes, if they inherit one X chromosome with the disease; they have another normal X chromosome to make the correct gene product. These individuals are considered carriers.
        Since male offspring have to receive a Y from their father, they will always inherit the colorblind or hemophilia allele from their mother; not the father.
        Males that have the disease can only pass the colorblind or hemophilia allele onto their daughters. Their sons will receive the Y chromosome.
        Females can only get X-linked recessive diseases if the mother happens to be a carrier of the disease (or has the disease) and the father also has the disease.
        Therefore sex-linked diseases are rare in females.
- - - - New alleles are created by random changes in the base sequence called mutations.
        There are a variety of different types of mutations that can be either harmful, neutral or beneficial, although it is very rare that mutation are beneficial.
        Mutations occur over extremely long periods of time over the course of evolution, however this can be sped up by other factors
        
        Radiation: gamma rays, alpha particles, short wave UV radiation, X-Rays
        
        Mutagenic chemicals: mustard gas and nitrosomes
        
        Consequences of Hiroshima and Nagasaki : radiation from atomic bombs caused cancer, still birth, malformations and death. Radiation Effects Research Foundation in Japan followed survivors and used people who were not exposed to radiation as a control group.
        
        853 / 17,448 tumours could be attributed to the radiation
        
        people who were infants at the time do not show a significant correlation between radiation and tumours. Although there were a few, this number was not "statistically significant" (urgh, but I get it, but urgh)
        
        people were stigmatised, nobody wanted to marry them/ have kids with them for fear of genetic diseases
        
        Chernobyl, Ukraine - explosions + fire in nuclear reactor resulted in workers immediately being exposed to radiation. Radioactive isotopes such as xenon, iodine, krypton and caesium were released throughout Europe.
        
        killed pine forest
        
        horses and cattles nearby the plant died of thyroid cancer
        
        wildlife started to thrive in sone in Chernobyl where humans were excluded
        
        drinking water and milk were contaminated with extremely high levels of radioisotopes
        
        bioaccumulation caused extremely high amounts of caesium in fish and lambs, which were banned as far as Wales
- - - - Chromosomes are replicated during S phase (Synthesis phase during interphase) - this is not part of actual meiosis
      - Prophase 1
        
        The nuclear envelope disintegrates.
        
        replicated chromosomes condense and become visible through supercoiling
        
        homologous chromosomes pair up and form bivalents or tetrads
        
        crossing over occurs between non sister chromatids.
        
        cross over points are called chiasmata
        
        spindle microtubules start to form
        
        Metaphase 1
        
        homologous pairs line up in the along cell's equator
        
        bivalents line up on either side of the equator, independent of other homologous pairs
        
        each bivalent has kinetochores that are attached to the spindle fibres in order to eventually be pulled apart.
        
        Anaphase 1
        
        Spindle fibres attached to the kinetochore of the homologous pairs, shorten and pull the homologous pairs apart.
        
        The chiasmata also break down and separate.
        
        One chromosome of each pair move to opposite poles of the cell. Disjunction
        
        Telophase 1
        
        Chromosomes begin to uncoil and nuclear envelope reforms.
        
        Spindle fibers and microtubules break down and disintegrate.
        
        Chromosome number reduces from 2n (diploid) to n (haploid); however, each chromatid still has the replicated sister chromatid still attached (not homologous pairs anymore).
        
        Cytokinesis occurs and the cell splits into two separate cells.
        No more replication is needed.
        
        Prophase 2
        
        Chromosomes condense again and become visible.
        
        Spindle fibers again form.
        
        Nuclear membrane disintegrates again.
        
        Metaphase 2
        
        Chromosomes line up along the equator.
        
        Centromeres contain two kinetochores that attach to spindle fibres from each pole.
        
        Resembles metaphase from mitosis.
        
        1 more item...
        
        Non Disjunction -
        
        error in meiosis where chromosomes fail to split. Can occur in anaphase 1 and 2, resulting in too many or too few chromosomes in a gamete.
        
        Down Syndrome or Trisomy 21 where a gamete will have 47 chromosomes
        
        leads to impairment in cognitive ability and physical growth, hearing loss, oversized tongue, shorter limbs and social difficulties
        
        Karotyping through chorionic villus sampling or amniocentesis
        
        Karyotyping is performed by collecting cells using one of two methods; chorionic villus sampling or amniocentesis.
        
        used for pre-natal diagnosis of chromosome abnormalities such as Down syndrome (Trisomy 21), Turner syndrome (XO), and Klinefelter syndrome (XXY).
        
        cells obtained by chorionic villus sampling and amniocentesis come from the embryo and not the mother, allowing doctors to analyze the DNA genome of the embryo.
        
        Amniocentesis procedure involves the extraction of a small amount of amniotic fluid (contains fetal tissues) with a needle, from the amnion or amniotic sac surrounding a developing fetus.
        -The fetal DNA is examined for genetic abnormalities through karyotyping.
        
        Chorionic villus sampling involves removing a sample of the chorionic villus(placental tissue) to test for genetic abnormalities through karyotyping. CVS can be carried out 8-12 weeks into the pregnancy.
        
        Crossing over: non-sister chromatids exchange segments of their chromosomes between each other. Genes between chromosomes are same although they may be different alleles. As cross over points are random, it increases genetic variation.