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Inherited change (Gene control (Transcription factors (necessary for…

- - - - requires substrate (inducer) to interact with regulatory enzyme causing transcription to occur
    - - its synthesis can be prevented by binding a repressor protein to the operator
  - - - the regulatory gene codes for a repressor
        
        the repressor binds to the operator region
        
        hence RNA polymerase cannot bind to DNA at promoter region
        
        no transcription of lacZ and Y
    - - lactose is taken up by the bacteria
        
        lactose binds to the repressor protein, distorting it and preventing it from binding at the operator site
        
        transcription is no longer inhibited and mRNA is produced; the genes have been switched on and transcribed together
  - - - Codes for proteins that regulate the expression of other genes
    - - Codes for proteins required by cells
  - - - PIF can bind to target promoter
      - amylase production increases
- - - - Prophase II
        
        Nucleolus and nuclear envelope disintegrate. Chromosomes move to opposite poles where centrioles are present. Spindle fibres develop at right angles to the spindle axis of Meiosis I
      - Metaphase II
        
        Chromosomes arrange themselves at the equator.
        The centromere of each chromosome is attached to the spindle fibre
      - Anaphase II
        
        Centromeres divide and pulled to opposite poles by the spindle fibres
      - Telophase II
        
        Chromatids uncoil, spindle disintegrates, both the nuclear envelope and nucleolus reform
        Cells divide to give a total of 4 cells
    - - Prophase I
        
        Chromatin begins to condense to form threadlike chromosomes
        
        Homologous chromosomes pair up via synapsis. Each pair constitutes a bivalent
        
        Homologous chromosomes begin to shorten and thicken, the sister chromatids separate
        
        Homologous chromosomes begin to repel each other, the position of the chiasmata become visible
        Chiasmata -sites where non sister chromatids may break and rejoin, a portion of one exchanging places with an equivalent portion of another
        
        enable the exchange of genetic material between homologous chromosomes (crossing over), forming new combinations of alleles on chromosomes of the gametes
        
        Nucleolus and nuclear envelope disintegrate, spindle forms
      - Metaphase I
        
        Bivalents arrange themselves at the equator. The arrangement of chromosomes is completely independent of the orientation of other bivalents
        
        Centromeres attach to individual spindle fibres
      - Anaphase I
        
        Homologous chromosomes separate. One pair is pulled to one pole and the other to the opposite pole
      - Telophase
        
        Chromosomes reach opposite poles of spindle, nuclear envelope and nucleolus reforms
        Each nucleus has a haploid number of chromosomes due to separation of chromosomes in anaphase I
    - - Formation of chiasmata
        
        crossing over of non-sister chromatids during prophase I leads to new combinations of alleles
      - Independent assortment during metaphase and anaphase I
      - Independent arragement of chromosomes at the equator during metaphase II and subsequent separation of chromatids during anaphase II
    - - Humans
        
        Oogenesis
        
        in the ovaries
        
        diploid cells divide by mitosis to produce dipoid oogonia, which grow to form primary oocytes
        
        meiosis I results to 1 haploid secondary oocyte and 1 polar body
        
        when a secondary oocyte is released into the oviduct each, if fertilization occurs meiosis II occurs and the cell is called an ovum
        
        Spermatogenesis
        
        in the testes
        
        diploid cells divide by mitosis to produce dipoid spematogonia, which grow to form primary spermatocytes
        
        meiosis I results to 2 haploid secondary spermatocytes
        
        meiosis II produces haploid spermatids, which mature into spermatozoa
      - Plants
        
        pollen grains
        
        in the anthers
        
        diploid pollen mother cells divide by meiosis to form 4 haploid cells
        
        the nuclei of these cells divide by mitosis, but no cytokinesis, each of the cells the have 2 nuclei
        
        the cells then mature into pollen grains
        
        embryo sacs
        
        a large, diploid, spore mother cell develops inside each ovule
        
        it divides by meiosis to produce 4 haploid cells, only 1 does not degenerate, which eventually develops into an embryo sac
        
        the embryo sac grows larger, and its haploid nucleus divides by mitosis 3 times, forming 8 haploid nuclei, one of these becomes the female gamete
- - - - Albinism
        
        due to a mutation in the gene for the enzyme tyrosinase, hence this results to an absence in the enzyme tyrosinase or the presence of inactive tyrosinase
        
        tyrosine cannot be converted into melanin, that is responsible for pigmentation
        typosine -> DOPA -> dopaquinone -> melanin
        
        pale blue/pink irises, very pale skin and hair , poor vision, jerky eye movements and a tendency to avoid bright light
        
        autosomal recessive , the phenotype will be expressed if the alleles are homozygous recessive
      - Huntington's disease
        
        dominant allele, heterozygous with 1 in 2 chance of passing on the condition to a child
        
        symptoms: involuntary movements (chorea) and progressive mental deterioration
        loss of brain cells and the enlargement of ventricles
        occur commonly in middle age
        
        patients have large number of repeats of the CAG triplet (stutter)
        the more repeats the earlier the condition appears
      - Haemophilia
        
        sex linked (recessive): found on X chromosome instead of Y
        
        blood fails to clot properly
        
        due to absence of factor VIII
      - Sickle cell anaemia
        
        HbS allele which is codominant
        those who are homozygous HbS will suffer from its symptoms, those who are heterozygous HbS will only show sickle cell trait
        
        Due to base substitution. Valine is coded for instead of glutamic acid, altering the tertiary structure of haemoglobin which alters the shape of red blood cells
        
        the red blood cells become useless in transporting oxygen
  - - - a length of DNA that codes for a particular polypeptide
    - - the position at which a particular gene is found on a particular chromosome
    - - a particular variety of a gene
    - - it s effect on a phenotype of a heterozygote is identical to its effect in a homozygote
    - - an allele that is only expressed when no dominant allele is present
    - - having 2 identical alleles of gene
    - - having 2 different alleles of a gene
    - - the characteristics of an organism, as a result of an interaction between its genotype and its environment
    - - the alleles possesed by an organism
    - - the presence of 2 genes on the same chromosome, that tend to be inherited together and do not assort independently
    - - crossing an organism showing a characteristic with its recessive form
    - - 1) the offspring resulting from a cross between an organism with a homozygous dominant genotype, and one with a homozygous recessive genotype
        2) the offspring resulting form a cross between 2 F1 organisms