Biology Blueprint Of Life section 3

  1. Outline Boveri's experiment
    -Experiments of sea urchin eggs

    - Sea urchins were suitable as they are: easily fertilised and have quick larval development
  2. Outline Suttion's experiment
    -Studied meiosis in celss of grasshoppers
  3. Outline the roles of Sutton and Boveri in identifiying the importance of chromosomes
    They discovered that:

    - Hereditary factors in cells are found in the nucleus only, not the cytoplasm and nucleus

    - Inherited factors are passed onto the next generation by random assortment during meiosis, not through gametes

    - The nature of chromosomes: they occur in set numbers in every cell. They do not disappear and reappear

    -A full set of paired chromosomes stores hereditary info
  4. Describe behaviour of chromosomes during meiosis
    Prophase 1

    Chromosomes coil up tightly into homologous pairs and line up

    Crossing over

    Arms of homologous chromosomes exchange genetic material 

    -This introduces genetic variation

    Chromosomes in each pair separate so that one chromosme from each pair moves into a daughter cell - AKA. random segregation

    Behaviour of chromosomes in meiosis impacts genetic variability
  5. What is variablity?
    -Different forms of a gene within a population 

    -Total of all alleles present in the gene pool of a population
  6. What are factors that influence variability?
    • -Genetics
    • -Environment
  7. Explain the role of gamete formation in variablity of offspring
    • o   Recombination of genetic material
    • à due to crossing over and random segregation

    • § 
    • Crossing over – homologous chromosomes exchange genes and resulting
    • combinations of alleles on chromatids differ from parent chromosomes

    • § 
    • Random segregation – independent assortment of genes, giving different gene
    • combinations

    • o   Therefore, gametes formed vary
    • genetically from the parent cells
  8. Explain the role of sexual reproduction in variability of offspring
    • o   Gametes that contain different
    • combinations recombine

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

    • § 
    • New combinations of genes occur in offspring – variability in population
  9. When do Mendelian ratios apply?
    In situations where genes assort independently and show dominance
  10. What is Co-dominance
    -Where both alleles are dominant and express themselves in the phenotype

    -Therefore does not show Mendelian ratios
  11. Describe sex-linkage
    • 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

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

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

    • Experiment
    • - First he mated a red eyed female with a white eyed male

    -This produced the Foffspring which were all red eyed

    -Now Morgan crossed 2 of the Fgeneration

    -In the Fgeneration, only the males had white eyes

    Morgan did many more experiments between red eyed females and white eyed males and had similar resultes with white eyes only appearing in male fruit flies
  13. What did Morgan's experiments show?
    • o   The gene for eye colour in fruit
    • flies is located on the X chromosome

    • o   Hereditary factors can be
    • exchanged between the X chromosomes of an individual
  14. What is the importance of Morgan's work
    Provided evidence for the chromosomal basis of sex-linkage
  15. Outline the ways in which the environment
    may affect the expression of a gene in an individual
    -Variation in organisms is either genetically determined or influenced by environment (nurture)

    • 1. Effect of Temperature 
    • -The sex of some animals is determinded by the temp at which they were incubated during their embryonic development. e.g. turtles

    • 2. Effect of Altitude
    • -Increasing altitude can stunt the phenotype of plants witht the same genotype. e.g. trees on a mountain- Engelmann Spruce

    • 3. Effect of Nutrients
    • - Hydrangea produces pink flowers in basic soils and blue flowers in acidic soils

Card Set
Biology Blueprint Of Life section 3