This is a question I'm troubled with as my exams are knocking at the door. I need help so I decided to post this here.
Here's what I know and understand about meiotic stages:
Specimen: Grasshopper (Gesonula punctifrons) testis whose 2n= 23
Note: The character in bold and italics is the identifying feature of the concerned stage.
Prophase:
Leptotene
- The uncondensed chromosomes are visible as a cloud of thin threads.
- Each chromosome consist of two chromatids which are not visible.
- The single darkly stained X chromosome is found at the periphery of the nucleus.
- Late in this stage the chromosomes attach themselves by telomeres to the inner membrane of the nuclear envelope forming a bouquet.
- Nuceolus and nuclear membrane are present.(not visible under compound microscope)
Zygotene
- The uncondensed chromosomes are visible as a cloud of threads.
- Homologous chromosomes undergo synapsis forming bivalent.
- The single darkly stained X chromosome is present slightly off the periphery of the nucleus.
- Nucleolus and nuclear membrane are present.(not visible)
Pachytene
- The chromosomes show some degree of condensation.
- The sister chromatids separate to form tetrad a structure with four chromatids.
- Crossing over between non sister chromatids of homologous chromosomes occur leading to formation of X shaped chiasmata.
- Nucleolus and nuclear membrane are present.(not visible)
Diplotene
- The chromosomes are thick and darkly stained.
- The chromosomes are wooly in appearance.
- The paired chromosomes separate from each other except for the chiasmata.
- Nucleolus and nuclear membrane begin to diappear.(can't be detected)
Diakinesis
- The chromosomes are thick and darkly stained.
- Terminalisation of chiasmata initiates.
- The bivalents appear rod, diamond or oval shaped.
- The nucleus and nuclear membrane disappear completely.
Metaphase-I
- The chromosomes are thick and darkly stained.
- Presence of twelve chromosomal elements (11 tetrad + X chromosome).
- The chromosomes are aligned at the equitorial plate.
- Terminalisation of chiasmata completes.
Anaphase-I
- Two groups of chromosome are in the act of separation.
- One group is with 11 autosomes and the other group with 11 autosomes and a X chromosome.
- The chromosomes are T or V shaped.
- Each chromosome is in dyad state.
- The centromere is undivided.
Metaphase-II
- There is 11-12 dyads present.
- The chromosomes are thick and darkly stained.
- The dyads are arranged in circle or flower like fashion.
- The chromosomes are rod like
Anaphase-II
- The sister chromatids of a dyad separate due to splitting of centromere.
- Two groups of chromosome are in the act of separation.
- One group is with 11 autosomes and the other group with 11 autosomes and a X chromosome.
- The chromosomes are rod like
Here's an image which has nearly all the stages except telophase.Can someone label the stages?
Here's what I feel about them:
Finally am I correct? How do I identify them correctly? Could you site some authentic references?