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UMUC
Biology 102/103
Lab 5: Meiosis
INSTRUCTIONS:

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carefully before completing the exercises/experiments and answering the
questions.
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Pre-Lab Questions
1.
Compare and contrast mitosis and meiosis.

Both mitosis and meiosis
are involved with the dividing of cells and the splitting of DNA between the new cells that are made.
They can also be parts of reproduction. In meiosis I, tetrad form and
crossing over occurs during prophase I. This does not occur during
mitosis. In metaphase I of meiosis, tetrads align at the spindle equator.
The paired chromosomes have a total of four chromatids each. In mitosis, dyads
align at the spindle equator. During meiosis two nuclear divisions are
required but in mitosis only one nuclear division required.
Mitosis
is the process, in the cell cycle, by which the chromosomes in the cell nucleus
are separated into two identical sets of chromosomes. Mitosis immediately
followed by cytokinesis resulting in two daughter cellscrating
two diploid cells that are genetically the same to each other and the parent
crating two diploid cells.
Meiosis
produces four daughter divisions and four daughter cells which results in four
haploid cells with half the chromosome number as the parent cell. During
meiosis there is crossing over of the DNA which means that the DNA on
two different chromosomes
can mix to create genetic diversity. This is why the daughter cells
are genetically not the same to each other and to the parent.

2. What major event occurs
during interphase?

During
interphase, the cell duplicates it DNA. The cell does most of its growing in
this stage. This phase also produces the components needed for cell division.
Interphase consists of three phases: one synthesis phase and two gap phases. During
early interphase the G1 (gap) stage growth occurs and in the late interphase
(the G2 stage). DNA replication takes place during mid-interphase the S
(synthesis) stage.

Experiment
1: Following Chromosomal DNA Movement
through
Meiosis

Data Tables
and Post-Lab Assessment
Trial 1 – Meiotic Division Beads Diagram:
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase I
Cytokinesis
Trial 2 – Meiotic Division Beads Diagram:
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase I
Cytokinesis

Post-Lab
Questions
1. Poloidy of the DNA at What
is the the end of meiosis I? What about at the end of meiosis II?
Meiosis
I is the reductional division because it halves the number of chromosome sets
per cell – a reduction from two sets (the diploid state) to one set (the
haploid state). The sister chromatids then separate during the second meiotic
division, meiosis II, producing haploid daughter cells.

2. How are meiosis I and
meiosis II different?
At
the end of meiosis I, both of the resulting daughter cells are haploid
(definitely not diploid). However, the chromosomes are still double-stranded. The
homologous pairs have already been separated. In humans, this means that the
original cell had 23 pairs of chromosomes, and the cells at the end of meiosis
I have 23 chromosomes (not pairs), each of which still have two sister
chromatids. At the end of meiosis II, there are a total of four daughter
cells, each of which is diploid. At this point, the sister chromatids have
separated from each other. In humans, this means that these gametes each have
23 chromosomes, each of which has one chromatid.

3. Why do you use
non-sister chromatids to demonstrate crossing over?
Crossing
over occurs between homologous chromosomes, which are not identical, as one
member of each pair of homologous chromosomes comes from the mother, and one
member comes from the father. Sister chromatids are identical and crossing over
would have no effect.

4.
What combinations of alleles
could result from a crossover between BD and bd chromosomes?

5. How many chromosomes
were present when meiosis I started?
There are 46 chromosomes at the beginning of meiosis
I.

6. How
many nuclei are present at the end of meiosis II? How many chromosomes are in
each?
There
are 4 nuclei and there are 2 chromosomes in each.

7. Identify two ways that
meiosis contributes to genetic recombination.

Crossing over
during prophase I, corresponding segments of non-sister chromatids are
exchanged and independent assortment of homologous chromosomes.
8. Why is it
necessary to reduce the number of chromosomes in gametes, but not in other
cells?
Gametes have
fewer chromosomes then other cells so that the offspring has the same amount of
chromosomes as the parents
9.
Blue whales have 44 chromosomes
in every cell. Determine how many chromosomes you would expect to find in the
following:

i. Sperm
Cell: 22

i.
Egg Cell: 22

iii.
Daughter Cell from Mitosis: 44

iv.
Daughter Cell from Meiosis II: 22

10.
Research and find a disease that
is caused by chromosomal mutations. When does the mutation occur? What
chromosomes are affected? What are the consequences?
The human body has 23
pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes. This
gives humans 46 chromosomes in total. Chromosomal genetic disorders occur when
chromosomes are partially or completely missing, altered or duplicated. An
example of a chromosomal genetic disorder is Down syndrome. Down syndrome is
the result of an extra, third copy of chromosome 21 being present in a person.
This extra chromosome results in extra protein production and upsets the body’s
balanced systems. During pregnancy chromosomal abnormalities can cause the
death of an embryo or fetus. Chromosomal disorders can result in mental retardation
or other developmental problems. Older pregnant women have a higher risk of
passing on chromosomal genetic disorders.

11.
Diagram what would happen if
sexual reproduction took place for four generations using diploid (2n) cells.
Experiment
2: The Importance of Cell Cycle Control
Data Tables
and Post-Lab Assessment
1.

2.

3.

4.

5.

Post-Lab
Questions
1.
Record your hypothesis from Step
1 in the Procedure section here.
I might
observe if all the chromosomes are normal except for one added chromosomes then
there will be an abnormality in the cell and it will shape different from the
rest.

2.
What do your results indicate
about cell cycle control?

3.
Suppose a person developed a
mutation in a somatic cell which diminishes the performance of the body’s
natural cell cycle control proteins. This mutation resulted in cancer, but was
effectively treated with a cocktail of cancer-fighting techniques. Is it
possible for this person’s future children to inherit this cancer-causing
mutation? Be specific when you explain why or why not.

4.
Why do cells which lack cell
cycle control exhibit karyotypes which look physically different than cells
with normal cell cycle.

5.
What are HeLa cells? Why are HeLa
cells appropriate for this experiment?