North Lake College Meiosis and Sexual Reproduction Lab Report

BioLab3
Meiosis and Sexual Reproduction Lab Report
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The lab report is unique each semester and checks have been put into place to ensure students are doing
their own work. Copying from other students or from outside resources will result in a zero on the
accompanying lab quiz.
I. Homologous Chromosomes
1. On a pair of homologous chromosomes, two alleles both code for blue eyes. Is this
condition considered homozygous or heterozygous?
2. What does heterozygous mean?
3. What is the difference between diploid and haploid cells?
4. Based on Lab, Exercise 1, what do the letters F and B represent?
II. Meiosis in Eukaryotes
1. At the end of meiosis II, are the resulting cells haploid or diploid?
2. Print the document found in Lab, Section 1. Use this document to follow along with
Exercise 2 and draw the beads as they appear at the end of each stage of meiosis I
and meiosis II. Sign and date your completed document and include with this lab
report.
III. Oogenesis and Spermatogenesis
1. What type of cells undergo meiosis?
2. Where does meiosis occur in human males and females?
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3. After fertilization occurs, are the resulting cells diploid or haploid in chromosome
number?
IV.
Summary of Mitosis and Meiosis
1. Compare mitosis and meiosis in the table below.
Mitosis
Meiosis
Number of chromosomes in
resulting cells
Number of nuclear divisions
V.
Meiosis and Life Cycle
1. How many total chromosomes do frogs have?
2. How many pairs of chromosomes do frogs have?
3. Determine whether the following types of cells are haploid (1n) or diploid (2n).
Type of cell
Haploid or
Diploid
Body cell
Sperm cell
Egg cell
Zygote
Summary Questions
1. Distinguish between meiosis and mitosis.
2. If a horse has 64 chromosomes before meiosis, how many chromosomes would exist
in each nucleus after meiosis I? After meiosis II?
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3. Is meiosis I or meiosis II most like mitosis? Explain why.
4. Name the male and female gametes that are produced by meiosis.
5. A trait is given the alleles aa. It this homozygous or heterozygous?
6. Before mitosis begins one sister chromatid of a duplicated chromosome has the allele
f, what allele will the other sister chromatid have?
7. What would happen if gametes were produced by mitosis instead of meiosis?
8. Differentiate between homologous chromosomes and sister chromatids.
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Lab 10 – Meiosis and Sexual Reproduction
EXERCISE 1 Construction of homologous chromosomes
1. Select twenty-four pop beads of one color and two magnets.
Construct two strands of pop beads consisting of five beads
of one color on one side of the magnet and seven beads of
same color on other side of the magnet. Each colored bead
represents a gene segment. Each strand represents a
chromosome. The two strands represent a replicated
chromosome (Figure 2).
2. Place a piece of tape with the letter F on the two top beads
of one set and a letter B on the two bottom beads. Join these
identical sections at their magnets representing the sister
chromatids of a replicated chromosome (Figure 2). The
magnets represent the centromere of the replicated
chromosome.
3. Select a second color of pop beads. Construct the
homologue to the replicated chromosome above. Construct
the same size structure as the one in steps 1 and 2. Place a
letter f on the top two beads of this set and a letter b on the
bottom two beads of the set. Join this set by their magnets.
4. You have constructed a model of two replicated
chromosomes that are homologous to each other. They have
two gene positions along their length labeled F, B, or f, b
(Figure 2).
sister chromatids
sister chromatids
Figure 2 Model of Replicated homologous chromosomes
EXERCISE 2 Modeling the stages of meiosis with pop beads
Meiosis I begins with a nucleus that is diploid. The
chromosomes are in their replicated state. Meiosis I has four
stages: Prophase I, Metaphase I, Anaphase I, and Telophase I.
1. Place the strands of pop beads constructed in Exercise 1 on
the lab table and draw a chalk circle representing the cell
nucleus around the two sets of pop beads. During interphase
the chromosomes are replicated and consist of two identical
parts termed sister chromatids. The replicated chromosomes
are randomly dispersed throughout the nucleus. Draw the pop
beads during Interphase (Figure 4). Be sure to include the
letters which represent the alleles.
2. Prophase I During this stage the nuclear envelope
disassociates and the replicated chromosomes become
condensed. The spindle apparatus will begin to extend
toward opposite poles. The spindle apparatus can be
represented with pieces of string as the spindle fibers and
two X’s as the centrosomes.
Prophase I is unique because homologous chromosomes
pair with each other and intertwine as a tetrad. This pairing
process is called synapsis. Using the 2 strands of each color
bead representing the homologous pair, illustrate synapsis.
During synapsis the non-sister chromatids exchange genes
at the F and f positions. When gene segments are exchanged
between non-sister chromatids of homologous chromosome
pairs, it is termed crossing-over (Figure 3). Remove one
color bead with the F and exchange with the other color
bead f. In late prophase, the homologous chromosome pairs
begin to move to the spindle equator as a tetrad and the
spindle fibers attach to the centromeres. Tie a length of
string to each of the two homologues at the centromere
region. Draw the pop beads during prophase I (Figure 4).
Include the letters indicating the alleles of each sister
chromatid.
Figure 3 Model of gene exchange between homologous chromosomes
3.
Metaphase I The centromeres of each homologue are
situated on opposite sides of the equator and spindle fibers
attach each one to opposite spindle poles. Position the loose
ends of the strings that are attached to each homologue at
opposite poles. Illustrate this step of meiosis I with the pop
beads. Draw the pop beads during metaphase I (Figure 4).
4.
Anaphase I During anaphase I, homologous chromosomes
separate and are pulled to opposite poles by the shortening
of the spindle fibers. Each homologue still contains two
sister chromatids. Demonstrate this step by pulling the
strings attached to each homologue in opposite directions
toward a pole marked with an “X” on your lab table. Draw
the pop beads during anaphase I (Figure 4).
5. Telophase I Each homologue is now at its respective pole and
cytokinesis is completed. Demonstrate this by drawing a chalk
circle around each of the two homologues, or replicated
chromosomes, representing the two cells formed by
cytokinesis. Draw the pop beads during telophase I (Figure 4).
The first meiotic division is complete. There are two
daughter cells each containing one replicated chromosome
consisting of two sister chromatids. The nucleus of each cell
is now haploid. This is why meiosis is known as reduction
division, reducing the number of chromosomes in the cells
by half. Indicate the alleles on each of the chromatids in the
2 cells.
Meiosis II occurs in each of the daughter cells that resulted
from meiosis I which contain half the amount of chromosome
material as the beginning cell nucleus. Meiosis II has four
stages: Prophase II, Metaphase II, Anaphase II, and Telophase
II.
6. Prophase II The sister chromatids are still attached by their
centromeres. The spindle apparatus forms again and begins
to migrate and spindle fibers attach to the centromeres.
Draw the pop beads during Prophase II (Figure 4). Indicate
the alleles on each of the chromatids.
7. Metaphase II The replicated chromosomes align along the
equator, the centromeres lying on the equator. The spindle
fibers attach each chromatid to opposite spindle poles. Draw
the pop beads during metaphase II (Figure 4). Indicate the
alleles on each of the chromatids.
8. Anaphase II The sister chromatids separate, moving toward
the opposite poles. After the sister chromatids separate, each
is an individual (not replicated) chromosome. Cytokinesis
(cytoplasmic division) begins during anaphase II. Separate
the two lengths of pop beads at the magnet and pull them
toward opposite polls. Change the chalk circle so that it dips
inward in the center to illustrate cytokinesis. Draw the pop
beads illustrating anaphase II (Figure 4). Indicate the alleles
on each of the chromatids.
9. Telophase II The two chromosomes are at opposite poles.
The nuclear envelope forms around each set and cytokinesis
is completed forming four cells. Four daughter nuclei now
exist. Each nucleus contains one individual chromosome of
the homologous pair originally present within the parental
nucleus. Illustrate telophase with the pop beads, and with
the use of chalk, complete the nuclear membrane around the
beads and the plasma membrane of the new cells formed by
cytokinesis. Draw the result of telophase II (Figure 4).
Indicate the alleles in each cell.
Interphase (2n)
MEIOSIS I
Prophase I
Metaphase I
Anaphase I
Telophase I
(Continued)
*
*
Figure 4 Stages of meiosis
(Meiosis continued)
*
MEIOSIS II
*
Prophase II
Metaphase II
Anaphase II
Telophase II
Figure 4 Stages of meiosis (continued)

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