®2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1 BIO Lab 07: Meiosis Meiosis Jesus answering said….”But from the beginning of the Creation, God made them male and female. For this cause a man shall leave his father and mother; and shall cleave to his wife. And they two shall be in one flesh….What therefore God hath joined together, let not man put asunder.” Mark 10:6-9 Introduction In a previous lab, you examined the process by which a diploid (2n) parent cell divides to produce two daughter cells with the same number and the same kind of chromosomes. The process, mitosis, results in diploid (2n) cells and is typical of ordinary tissue growth. Meiosis is cell division in which a diploid (2n) parent cell divides to produce four daughter cells with half the number of chromosomes called the haploid (n) number. The daughter cells are specialized gametes designed to restore the diploid number at fertilization as shown. Not only is chromosomal number reduced in meiosis, but any given chromosome in the parent cell may differ from the same chromosome in the daughter cell due to one or more crossover events. In this lab, you will follow the movement of chromosomes through meiosis in order to create four haploid daughter cells. Definitions Definitions involved in meiosis: ❖ Allele – Alternate forms of the same gene found at the same location on a homologous chromosome ❖ Chiasma – The area on homologous chromosomes where crossover occurs ❖ Chromatid – One of two identical copies of chromosomes held together by a centromere, formed when a chromosome replicates itself during cell division. Also called “sister chromatids” ❖ Chromosome – Highly condensed structure of DNA surrounded by proteins found when cells are undergoing division to ensure that genetic information is divided equally between the two resulting daughter cells ❖ Crossover – A process of genetic exchange between homologous chromosomes occurring in the tetrad structure during meiosis I, resulting in recombinant chromosomes ❖ Diploid – Cells that have two copies of each chromosome, one from each parent (called 2n) ❖ Gamete – A cell containing a haploid number of chromosomes ❖ Gene – A DNA sequence on a chromosome coding for a specific protein ❖ Haploid – Cells that have one copy of each chromosome (called n) ❖ Homologous Chromosomes – One chromosome from each homologous pair comes from mother (maternal chromosome) and one comes from father (paternal chromosome). They are similar but not identical – each have genes in same order but alleles for each trait may differ. ❖ Ploidy – The number of copies of chromosomes in a cell. In animals, usually diploid (2n) or haploid (n).
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®2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1
BIO Lab 07: Meiosis
Meiosis Jesus answering said….”But from the beginning of the Creation, God made them male and female. For this
cause a man shall leave his father and mother; and shall cleave to his wife. And they two shall be in one
flesh….What therefore God hath joined together, let not man put asunder.” Mark 10:6-9
Introduction
In a previous lab, you examined the process by which a diploid (2n) parent cell divides to
produce two daughter cells with the same number and the same kind of chromosomes. The
process, mitosis, results in diploid (2n) cells and is typical of ordinary tissue growth.
Meiosis is cell division in which a diploid
(2n) parent cell divides to produce four daughter
cells with half the number of chromosomes
called the haploid (n) number. The daughter
cells are specialized gametes designed to restore
the diploid number at fertilization as shown.
Not only is chromosomal number reduced in
meiosis, but any given chromosome in the
parent cell may differ from the same chromosome in the daughter cell due to one or more
crossover events. In this lab, you will follow the movement of chromosomes through meiosis in
order to create four haploid daughter cells.
Definitions Definitions involved in meiosis: ❖ Allele – Alternate forms of the same gene found at the same location on a homologous chromosome
❖ Chiasma – The area on homologous chromosomes where crossover occurs
❖ Chromatid – One of two identical copies of chromosomes held together by a centromere, formed
when a chromosome replicates itself during cell division. Also called “sister chromatids”
❖ Chromosome – Highly condensed structure of DNA surrounded by proteins found when cells are
undergoing division to ensure that genetic information is divided equally between the two resulting
daughter cells
❖ Crossover – A process of genetic exchange
between homologous chromosomes occurring in
the tetrad structure during meiosis I, resulting in
recombinant chromosomes
❖ Diploid – Cells that have two copies of each
chromosome, one from each parent (called 2n)
❖ Gamete – A cell containing a haploid number of
chromosomes
❖ Gene – A DNA sequence on a chromosome
coding for a specific protein
❖ Haploid – Cells that have one copy of each
chromosome (called n)
❖ Homologous Chromosomes – One chromosome from each homologous pair comes from mother
(maternal chromosome) and one comes from father (paternal chromosome). They are similar but not
identical – each have genes in same order but alleles for each trait may differ.
❖ Ploidy – The number of copies of chromosomes in a cell. In animals, usually diploid (2n) or haploid
(n).
®2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2
BIO Lab 07: Meiosis
❖ Recombinant Chromatid – Chromatid produced when segments of DNA are exchanged at a cross
over event during Prophase I or Metaphase I
❖ Somatic Cells – Diploid cells not involved in gamete formation
❖ Tetrad – Four homologous chromosomes made up of two sister chromatids and formed during the
prophase of meiosis
Learning Objectives: • Model the steps of meiosis in order to gain a better understanding of the process
• Compare and contrast meiosis and mitosis events and processes
• Examine crossover and the effect it has on chromosomes in daughter cells
Materials Required: From Biology Kit Student Supplied
Chenille Stems (pipe cleaners) (4 lengths)
Beads, Color 1 (10)
Beads, Color 2 (10)
Safety
• Beads are a choking hazard. Keep away from small children. Do not put in mouth.
Preparation:
1. Build Paternal Chromosomes:
• You will need a total of 10 beads of
one color
• Use the diagram to the right to guide
your construction
• Chromosome 1:
▪ Place 2 beads on a pipe cleaner
▪ Tie a knot in the pipe cleaner to
model the centromere
▪ Place 1 remaining bead on the
end
▪ Secure both ends so the beads do
not fall off
▪ Duplicate this so that you have
two Paternal copies of
Chromosome 1
▪ See figure to the right
• Chromosome 2:
▪ Place 1 bead on a pipe cleaner
▪ Tie a knot in the pipe cleaner to model the centromere
▪ Place 1 remaining bead on the end
®2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3
BIO Lab 07: Meiosis
▪ Secure both ends so the beads do not fall off
▪ Duplicate this chromatid so that you have two Paternal copies of Chromosome 2
▪ See figure to the right
2. Build Maternal Chromosomes:
• You will need a total of 10 beads of a different color
• Use the diagram above to guide your construction
• Chromosome 1:
▪ Using 3 beads of a different color, construct Maternal Chromosome 1
▪ Duplicate this so that you have 2 Maternal copies of Chromosome 1
• Chromosome 2:
▪ Using 2 beads of the maternal color, construct Maternal Chromosome 2
▪ Duplicate this so that you have 2 Maternal copies of Chromosome 2
3. Let us review what you have:
• Sometime during Interphase, S-phase will occur, in which each chromosome will
duplicate
• The cell will have copies of each chromosome
• Using our organism today as an example, we have:
Duplicate copies (or sister chromatids) of Chromosome 1 derived from this
organism’s mother
Sister chromatids of Chromosome 1 derived from this organism’s father
These are called Homologous Pairs
Genes at equivalent points on the maternal gene and the paternal gene are called
homologous genes or alleles
• The figures below show two sets of homologous pairs of chromosomes
®2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4
BIO Lab 07: Meiosis
Experiment 1 – No Crossover Use your text and notes to review the important processes at each stage of Meiosis.
1. Assemble a tetrad
• Pair the homologous chromosome you have constructed into a tetrad
• Locate the cell diagrams following Experiment 2 below
▪ Use the cell outlines to place your models in, or as a model to draw your own cell
outline
• Locate Table 1 in Lab Report and use it to describe your models
2. Using the bead “chromosomes”, model each stage of meiosis and cytokinesis:
• Prophase I and II
• Metaphase I and II
• Anaphase I and II
• Telophase I and II
• Cytokinesis I and II
3. As you model each stage, use Table 1 to note your findings, especially:
• Major activities that occur in each step
• The correct number of chromosomes present in the cell for each phase
• The notable appearance or disappearance of structures such as:
▪ Diploid or haploid state
▪ Number of chromosomes in cell
▪ Centromeres
▪ Chromatin
▪ Sister chromatids
▪ Spindles and spindle fibers
▪ Centrioles
▪ Metaphase plate
▪ Nuclear envelope
▪ Cleavage furrow
▪ Other structures that appear or disappear
3. Perform Data Analyses and Conclusions
®2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 5
BIO Lab 07: Meiosis
Experiment 2 – Crossover Use your text and notes to review Crossover events during Meiosis.
1. Assemble chromosomes
• Reassemble the two homologous chromosomal pairs as you did before
• Locate Table 2 in Lab Report and use it for discussing your models
2. Model a Crossover Event at Prophase I
• Bring Homologous Pair 1 close together
• Create a chiasma
Cross ONE (and only one) sister chromatid of one pair with the
homologous sister chromatid of the second pair
• Exchange an equal number of beads between the two pairs
• Ensure that the resulting recombinant chromosomes are equal in
length but now have different combination of colors
Describe in detail the resulting homologous pair in Table II
3. Model the remaining stages of Mitosis and Cytokinesis:
• Prophase II
• Metaphase I
and II
• Anaphase I
and II
• Telophase I
and II
• Cytokinesis
4. As you model each stage
• Pay attention to the following:
Crossover event:
• Follow the new recombinant chromatids
• Note which cells the new recombinant chromatids end up in
• There are 4 cells at the end of meiosis, describe how they differ.
Make sure you indicate the correct number of chromosomes present in each cell
for each phase
• Describe the notable appearance or disappearance of:
Recombinant chromatid, haploid, diploid, spindles and spindle fibers, centrioles,