Genetics 3

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Genetics 3
2012-07-06 22:43:38
Dr Troy Bray

Lecture test number one.
Show Answers:

  1. What is the difference between Isogamous and Heterogamous organisms?
    Isogamous organisms have gametes of equal size, structure, & motility. While Heterogamous have differences.
  2. Describe the gametes of Oogamous organisms.
    Larger non-motile egg; smaller motile sperm.
  3. What are the five subdivisions of Prophase 1 of meiosis?
    • Leptotene
    • Zygotene
    • Pachytene
    • Diplotene
    • Diakinesis 
  4. What takes place in Leptotene?
    • Sister chromatids condense & become visible.
    • Often take on a horse shoe shape; ends associated with proteins on the nuclear lamina. 
  5. What takes place in Zygotene?
    • Synapsis (homologous sisters join along their lengths)
    • Bivalents are formed and are joined at synaptonemal complex to form Tetrads.
  6. What happens in Pachytene?
    • Crossing over occurs; forming recombinant DNA.
    • Enzymes that are involved : Endonucleases (cut), DNA Ligases (glue ends), DNA polymerases (repair)
    • Chiasma is the site or crossing over. 
  7. What happens in Diplotene?
    • Synaptonemal complex dissolves.
    • Bivalents come appart.
    • In females meiosis is arrest at this stage when female embryos are 5 months and will not resume until puberty. 
  8. What happens in diakinesis?
    • Nuclear membrane disappears completely.
    • Nucleolus disappears. 
  9. Describe the various system of sex determination.
    • XY system : Mammals. Male is heterogametic and female is homogametic.
    • XO system : Insects. Male has one chromosome and gemale is homogametic.
    • ZW system : birds and fish. Male is homo gametic and females are heterogametic. 
  10. What is a test cross?
    Crossing an unknown genetotype with a homosygous recessive organism to conclude the genotype of the unknown parental organism.
  11. What is a reciprocal cross?
    A cross to determine if a gene is located on the X chromosome.
  12. Males transmit thier X chromosome to _____ offspring.
  13. Females transmit X chromosome to ______ offspring.
    Male and female.