Name:_____________________________
Mitosis and Meiosis Study Guide
Mitosis:
DIPLOID
a. What does diploid mean?
A cell that has two matched sets of chromosomes in the cell nucleus, one set
from each parent (2n). (46 in humans)
b. Are most human cells diploid?
Yes. All somatic cells
c. How many pairs of homologous chromosomes are present in a human somatic cell?
23 pairs
d. What is the best description of homologous chromosomes?
(choose the best response)
(1) they are the same size and shape
(2) they contain the same types of genes in the same order
(3) they generally contain different versions (alleles) of many of their genes
(4) all of the above
e.. Define homologous chromosome.
Homologous chromosomes are chromosomes that are paired during meiosis. They consist of
four chromatids. One pair comes from the father and the other, from the mother
f. Contrast gene and allele.
Gene-A segment of the DNA that codes for a specific trait.
Allele-An allele is one of two or more forms of a gene (one from father and one from
mother)
INTERPHASE
a. How do sister chromatids differ from chromosomes?
Sister chromatids are two identical copies of a chromatid connected by a centromere.
(Copied during the S-Phase)
b. What is the centromere?
Links sister chromatids. Spindle fibers connect to the centromeres.
c. Contrast chromatin and chromosome.
Chromatin is thin threadlike genetic material that is present during most of the cell’s life
cycle.
A Chromosome is condensed genetic material that is present during mitosis and can be seen
by a microscope.
d. What is the main role of INTERPHASE?
Cell growth and development. It is most of the cell’s life cycle.
e. What occurs in the SPhase and why is it important?
DNA replication. The amount of DNA must double so that the cell has the appropriate
number of chromosomes after mitosis.
MITOSIS
PROPHASE
a. Are the two sister chromatids that are connected by a centromere identical to one
another or do they contain different alleles? Explain.
They are identical so that each cell will receive an exact copy of the DNA after mitosis.
b. As noted above, these structures are called replicated chromosomes (or, in many
books, simply chromosomes). Replicated chromosomes are quite different from the
unreplicated chromosomes seen earlier. Compare replicated chromosomes to
unreplicated ones (by filling in the blanks below).
(1) the amount of DNA in a replicated chromosome is__2___ times the amount
of DNA in an unreplicated chomosome
(2) the number of copies of each gene in a replicated chromosome is __2___
times the number of copies in an unreplicated chromosome
(3) each replicated chromosome contains _2____ (insert number) complete
copies of genetic info.
(4) the copies of genetic information in each chromosome are
__identical______________ (identical, homologous, or complementary)
c. Will the homologous replicated chromosomes pair with one another during mitosis?
Explain.
No. They line of independently from one another since the cell will receive an exact copy.
Homologous pairing only occurs during MEIOSIS.
d. A diploid human cell contains 46 unreplicated chromosomes in early interphase. How
many sister chromatids will be present in the human cell during prophase of mitosis?
92
f) Summarize the events of Prophase.
The chromatin condenses and turns into visible chromosomes. Remember that the DNA has
already replicated at this point!
The nucleus and nucleolus disappear.
Spindle fibers form and attach to the centrioles.
(This is the longest phase of mitosis)
METAPHASE
a. How many replicated chromosomes would be on the metaphase plane in a human
cell undergoing mitosis?
46
b. Summarize metaphase.
The chromosomes line of in the center of the cell.
Spindle fibers attach to the centromeres of the chromosomes.
ANAPHASE
a. What are daughter chromosomes?
The individual chromosomes that are pulled apart and will go in the nucleus of the two new
cells.
b. Are the two sets of daughter chromosomes, the one moving toward the left and the
other toward the right, identical or non-identical?
Identical
c. Are the two sets of daughter chromosomes identical to those in the parent cell?
Identical
d. What is accomplished by this process?
Two sets of identical chromosomes.
e. Summarize anaphase.
Sister chromotids are pulled apart by the spindle fibers into individual chromatids.
TELOPHASE
a. Summarize what happens in Telophase.
The nuclear envelope and nucleolus reform.
Chromosomes begin to uncoil.
Spindle fibers disappear.
CYTOKINESIS
a. Does the parent cell still exist?
No, but the two new cells are identical to the old parent cell.
b. Are the daughter cells identical or different from the parent cell?
Identical (except smaller)
d. Overall, what has been accomplished by mitosis?
One cell divides into two exact copies
Meiosis:
a. Summarize the events of Interphase I, Prophase I, Metaphase I, Anaphase I, and Telophase I.
Interphase: G1-Cell growth/development, S-phase: DNA replication, G2 prep for meiosis
Prophase I: Chromatin thickens into chromosomes, nucleus/nucleolus disappear. Synapsis
occurs to form tetrads. Crossing over of tetrads occurs to increase genetic variation.
Metaphase I: Homologous Chromosomes (tetrads) line up at the equator instead of individual
chromosomes. Independent Assortment insures genetic variation.
Anaphase I: Tetrads split. Sister chromatids remain attached.
Telophase I: Nucleus and nucleolus reappear.
NO INTERPHASE
Prophase II: same as prophase in mitosis
Metaphase II: same as mitosis
Anaphase II: same as mitosis
Telophase II: same as mitosis
Cytokinesis: same as mitosis except that 4 cells are produced by the two divisions instead of
2.
b. What are the differences in each phase of Meiosis I compared to Mitosis?
• Meiosis reduces the number of chromosomes by half.
• Daughter cells differ from parent, and each other.
• Meiosis involves two divisions, Mitosis only one.
• Meiosis I involves:
– homologous chromosomes pair up (tetrads).
– crossing over of non-sister chromatids.
– In Metaphase I, homologous pairs line up at metaphase plate.
– In Anaphase I, sister chromatids do NOT separate.
– End Product, separation of homologous pairs of chromosomes, rather than
sister chromatids of individual chromosome.
c. Describe the events of Prophase II, Metaphase II, Anaphase II, Telophase II, and Cytokinesis.
NO INTERPHASE
Prophase II: same as prophase in mitosis
Metaphase II: same as mitosis
Anaphase II: same as mitosis
Telophase II: same as mitosis
Cytokinesis: same as mitosis except that 4 cells are produced by the two divisions instead of
2.
d. How does Meiosis create haploid cells? What does haploid mean?
Meiosis replicates chromosomes in the Sphase of interphase, just as mitosis does. However
meiosis involves 2 cell divisions so as to reduce the number of chromosomes in half.
e. After meiosis, does the parent cell still exist?
No. 4 new and different cells exist.
f. How are the daughter cells related to one another?
They are not identical. They will each have a different combination of genetic material.
g. How are the daughter cells related to the parent cell?
They are not identical. Each cell has a different combination of the parent cell’s
chromosomes.
h. What happens to the number of chromosomes when a sperm and egg cell fertilize?
The combination of half + half gives the fertilized cell the diploid number of chromosomes.
i. What is a karyotype?
It is a picture of an individual’s chromosomes.
j. Explain how non-disjunction can cause genetic disorders like Downs syndrome.
During anaphase I, instead of the tetrad splitting both homologous chromosomes go to one
side. Therefore, after the first division one cell has both sets and the cell has none. After the
2nd division, 2 of the cells will have 2 chromosomes each and the other 2 cells will have zero.
When the sperm and egg meet, the fertilized cell will then have either 3 or 1 chromosomes
instead of the normal 2.
h. Overall, what has been accomplished by meiosis?
4 gametes that are each different from each other have been produced for reproduction. For
males, 4 sperm are created. Females will create only one egg, however, and the other 3 cells
(polar bodies) will be not be used. This is because the egg has to contain all of the cytoplasm
and organelles for the potential zygote since the sperm does not contain organelles.
Sample Questions: