Blueprint of life section 3~

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271551
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Blueprint of life section 3~
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2014-04-22 20:39:57
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Biology blueprint life section onwards
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  1. Describe the chemical nature of chromosomes
    Chromosomes consist of 40% DNA and 60% protein
  2. Describe the chemical nature of genes
    Short lengths of DNA make up genes

    o Genes have same chemical composition as DNA
  3. What is DNA
    DNA is the molecule that carries hereditary information

    o Carries, in coded form, instructions for the formation/functioning of cells

    o Structure allows self replication

    o Can be transferred by gametes (as chromosomes) from one generation to the next
  4. Identify that DNA
    is a double-stranded molecule twisted into a helix with each strand comprised
    of a sugar-phosphate backbone and attached bases
    • Bases are :
    • -Adenine (A)
    • -Thymine (T)
    • -Cytosine (C)
    • -Guanine (G)

    Adenine is complementary to Thymine (A-T)

    Cytosine is complementary to Guanine (C-G)

    -Bases are attached to a sugar molecule
  5. Explain the relationship between the
    structure and behavior of chromosomes during meiosis and the inheritance of
    genes
  6. What is 'variability'?
    -Different forms of genes within a population

    -Total of all alleles present in the gene pool of a population

    -Can be influenced by: genetics, enviornment, or both
  7. Explain the role of gamete formation and
    sexual reproduction in variability of offspring
    In gamete formation

    • -Recombination of genetic material
    • -Therefore, gametes formed vary genetically from the parent cells

    In sexual production

    -Gametes that contain different combinations recombine

    • -Recombination of genetic material and possibility of the many different
    • gametes fusing increases variation

    • -New combinations of genes occur
    • in offspring:variability in population
  8. What is 'Codominance'?
    - Where both alleles are dominant and express themselves in the phenotype 

    - Both alleles are independently and equally expressed

  9. Describe sex-linkage and sex linked genes
    • o   One sex chromosome is ‘X’ while
    • another is ‘Y’

    o   Female – XX

    o   Male – XY

    • o   Therefore, the Y (male gamete)
    • determines the sex of offspring

    • o   Male gamete is shaped differently
    • to X chromosome (missing an arm to give it a Y shape)

    • o   The X chromosome may have some
    • genes that the Y chromosome does not because it is missing its arm

    • § 
    • These are called SEX LINKED GENES

    • § 
    • Physically linked to sex chromosomes and inherited together with sexual
    • traits



  10. Why do sex-linked genes and alleles that display co-dominance not produce Mendelian ratios?
    • -Mendelian ratios apply in situations where genes assort independently and
    • show dominance

    -Mendel’s experiments did not show sex-specific effects 

    -Therefore, does not show Mendelian ratios
  11. Describe the work of Morgan that led to the understanding of sex linkage
    • Worked with fruit flies
    • -Normally have red eyes
    • -Mutant male flies: white eyes

    Experiments

    Cross 1- Cross bred pure breeding parents to obtain F1 hybrid offspring (White eyed male and Red eyed female)

    Cross 2- Crossed the F1 hybrid offspring to obtain F2

    o In the F2 generation only the maled had white eyes


    -Morgan did many more experiments and had similar results with white eyes only appearing in males

    -Found that his results could not be accounted for by simple Mendelian ratios

    - Therefore concluded that the gene for eye colour is located on the X chromosome
  12. Outline ways in which the environment may affect the expression of a gene in an individual
    • Some variation is organisms are genetically determined while others are
    • influence by environment (nurture)

    • -Nature vs Nurture
    •   
    • -Most arise as an interaction between both factors

    e.g. Siamese Cats

    • -Darkness of the tips of ears, tail, face, legs determined by temperature
    • of environment
  13. What is DNA composed of?
    2 polynucleotides wound together in a helix
  14. What does a nucleotide consist of?
    • -A sugar
    • -A phosphate
    • -A nitrogen base
  15. A chromosome is an....?
    organised structure of DNA and protein
  16. What is a 'codon'?
    - A unique triplet code

    -is the basis for information transfer
  17. Describe the process of DNA replication
    1. DNA double helix unwinds

    2. DNA unzips (2 strands separate)

    3. Nucleotides are added to each single strand
  18. What is DNA replication?
    The production of 2 identical double stranded molecules of DNA from an original double helix molecule
  19. What is the significance of DNA replication
    -Necessary preliminary step for cell division

    -Genetic material is transmitted

    -Replication ensures that the genetic code of a cell is passed to each new daughter cell that arises from it

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