Meiosis

Yep, still working here also (^8, below are some references:

• The Hawley Labs explaination of Meiosis.
• Cytogentic Terms Index
• Meiosis
• Basic lecture notes
• On-line study guide
• Introduction to Genetics and Meiosis and Mendelian Genetics - From University of California, Santa Barbara

Below is a response to a person asking about a teacher that was teaching meiosis using the stages as 'double diploid' etc.

Here is a VERY simple example of what occurs:

        1. The cell dublicates the DNA 'double diploid', since it
                now has 4 copies of each chromosome.
        2. The Cell divides, creating 2 cells each with one set of
                chromosomes (ie. 2 chromosomes each).  Your teacher
                would call this 'diploid', regardless of what the books say.
        3. The cell divides again (Note: no DNA replication this time)
                creating to truely haploid cells (a total of 4 cells
                all haploid and only one set of chromosomes).  Both your
                teacher and the books would agree.

The nomenclature is just pretty poor it seems, the books are less clear nomenclature
than your teachers.  What is correct??  (Who is to say, but your teacher is
grading so I would go with what she says. Besides your teachers nomenclature
makes more sense according to definitions of the words.)

        Double Diploid - 4 copies of the chromosome
        Diploid - 2 copies of the chromosome
        haploid - 1 copy of each chromosome  (Half)

Here is the dictionary definitions:

diploid cell:
   Cell having its chromosomes in homologous pairs, and thus having 2 copies
   of each autosomal genetic locus. The diploid number (2n) equals twice the
   haploid number and is the characteristic number for most cells other
   than gametes.

haploid:
   Describes a nucleus, cell or organism possessing a single set of unpaired
   chromosomes. Gametes are haploid.

meiosis:
   A specialised form of nuclear division in which there two successive
   nuclear divisions (meiosis I and II) without any chromosome replication
   between them. Each division can be divided into 4 phases similar to
   those of mitosis (pro-, meta-, ana- and telophase). Meiosis reduces the
   starting number of 4n chromosomes in the parent cell to n in each of
   the 4 daughter cells. Each cell receives only one of each homologous
   chromosome pair, with the maternal and paternal chromosomes being distributed
   randomly between the cells. This is vital for the segregation of genes. During
   the prophase of meiosis I (classically divided into stages: Leptotene, Zygotene,
   Pachytene, Diplotene and Diakinesis), homologous chromosomes pair to form
   bivalents, thus allowing crossing-over, the physical exchange of chromatid
   segments. This results in the recombination of genes. Meiosis occurs during
   the formation of gametes in animals, which are thus haploid and fertilization
   gives a diploid egg. In plants meiosis leads to the formation of the spore by
   the sporophyte generation.

Go to Chapter 3: 'Overview of the Cell Cycle'

WWW Cell Biology Course Index

Go to Chapter 3: 'Mitosis'

Please send questions/comments/suggestions to: Mark Dalton at markwdalton@gmail.com.