LAB #11: MEIOSIS LAB
Required Materials:
1. Prepared slides of Lillium
a. Early prophase
b. Late prophase
c. First division – Meiosis I
d. Second division – Meiosis II
e. Pollen tetrads
2. Meiosis models
Introduction
Meiosis, the second type of cell division, functions in plants and animals to reduce the genetic
information within the diploid parental cell by half, producing haploid cells that will either directly or
indirectly take place in reproduction. The process of this reduction is not random. When a new
individual is produced, their parents must supply all of the genes necessary to control their biological
processes. If a mother cell has 46 chromosomes and reduces the genetic content to 23 chromosomes
randomly, there is the chance that the daughter cells will lack specific chromosomes. To prevent this,
living organisms evolved chromosome pairs (i.e. 2 chromosome 1’s, 2 chromosome 2’s etc….). When the
mother cell divides by meiosis, the homologuous chromosomes separate – one into each daughter cell.
At the end of meiosis, each daughter cell is haploid – has half the number of chromosomes (but the
same chromosomes) as the parental cell.
Meiosis occurs in two phases : Meiosis I and Meiosis II. Each phase has the same stages as mitosis and
many similarities with this division process can be found in mitosis. However, there are some distinct
differences. In Metaphase I of Meiosis I, the duplicated homologous chromosomes line up on the
spindle in a unique way – a tetrad – made up of four total chromatids (see your lecture notes and text).
In Anaphase I, the duplicated chromosomes do not split into individual chromatids, but move as intact,
duplicated chromosomes to the opposite poles of the cells. Telophase I and cytokinesis is identical to
mitosis and the parental cell splits into two daughter cells. However, the physical conformation of the
DNA is unique. Let’s take the case of humans - these daughter cells have 23 duplicated chromosomes or
46 chromatids in total.
In the second round of Meiosis or Meiosis II, the phases are very much like mitosis, including the way
the duplicated chromosomes line up during Metaphase II and split during Anaphase II. However, at the
end of this stage you have two more daughter cells – for four total.
Procedures:
1. Phases of Meiosis I and II in the plant Lillium: the slides you will observe are sections through the
anthers of the flower buds. The parental cells in the four pollen sacs are undergoing meiosis to
produce spores. The spores will develop and produce the male gamete (sperm) just prior to
fertilizing the female’s ovum in the carpel (containing the ovaries). Observe the prepared slides
of these pollen sacs at various stages of meiosis. Draw and label what you see in your lab
notebook.
a. Prophase I: Observe the prepared slides of these pollen sacs known to be in early and
late prophase of meiosis. During Prophase I, homologous chromosomes will “pair up”
and lie next to each other to produce a tetrad. This process is known as synapsis.
Genetic information may be exchanged between chromatids at this stage in a process
known as crossing over. Try to find these synapsing chromosomes and draw them in
your notebook. How many cells containing these structures can you find?
b. Metaphase I and Anaphase I – you will find these stages on the slides labeled First
Division. The tetrads line up and attach to the spindle at Metaphase I and intact,
duplicated chromosomes split up at Anaphase I – still comprised of attached
chromatids. Identify these stages and count how many cells you can find undergoing
these stages.
c. Telophase I, Prophase II, Metaphase II and Anaphase II are all found in the slide marked
Second Division. The two cells resulting after meiosis I are held together by a single
casing product and are referred to as a dyad. Try to find these structure in the slide.
These dyads will be at different stages of meiosis II so observe and document them
carefully.
d. Telophase II: After meiosis, the four haploid daughter cells are held together in a single
casing. This is also called a tetrad. Therefore the slide for this phase is labeled tetrad. Do
not mix it up with the tetrads of chromosomes that form during meiosis I.
2. Meiosis models: Take a look at the representative models for each meiosis stage and compare
them to your drawings and observations.