BIO152: Mitosis & Meiosis
a review & introduction
Lecture 12
October 23
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Lecture 12 Outline
Pre test
Key terms
Cell cycle review (just the basics)
Mitosis
Meiosis
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Online resources:
meiosis & mitosis
Check out the animations
http://www.cellsalive.com/meiosis.htm
http://www.cellsalive.com/mitosis.htm
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Background review
Draw out each phase of
1.
Mitosis Freeman Figure 11.9 p 234-5
2.
Cell cycle– know the stages p 241:
a)
b)
c)
d)
3.
Mitosis
Gap 1
DNA synthesis (S)
Gap 2
Meiosis Figure 12.4
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Testing your understanding
If you can answer the following questions
(correctly!) you understand the basic
mechanism and importance of meiosis.
Don’t worry if you can not answer all of the
questions yet—you should by the end of this
section!
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Pre-test sample questions
1.
A human cell (2n) has 46 chromosomes. Following
mitosis, the daughter cells would each have a total
of ______ chromosomes (?n). After meiosis I, the
two daughter cells would have
_____chromosomes (?n), and after meiosis II
______ chromosomes (?n).
A.46 (2n), 46 (2n), 46 (2n)
B.46 (2n), 23 (n), 23 (n)
C.23 (n), 23 (n), 23 (n)
D.46 (2n), 12 (0.5n), 12 (0.5n)
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2. The process of meiosis produces four cells
with non-identical chromosomes. This
diversification occurs during:
A. telophase I
B. prophase I
C. metaphase II
D. prophase II
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3. Which of the following is unique to mitosis
and not a part of meiosis?
A.homologous chromosomes pair forming
bivalents
B.homologous chromosomes cross over
C.chromatids are separated during anaphase
D.homologous chromosomes behave
independently
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4. The Thompson seedless grape is triploid,
with three copies of each chromosome.
Which phase of cell division would you
expect triploid cells to be unable to complete.
A. meiosis I
B. S
C.meiosis II
D.mitosis
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5. The stage of meiosis where cells become
haploid.
A. prophase I
B. prophase II
C. anaphase I
D. anaphase II
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This is easier than it looks
6. Assume that a somatic (non-sex) cell of a human
contains about 13 picograms of DNA in the G1
phase. How many picograms of DNA would be
expected in a gamete (G1) produced by this
individual?
A. 6.5
B. 26
C. 13
D. 52
E. none of the above
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7. After telophase I of meiosis, what is the
chromosomal makeup of each daughter cell?
A. Diploid; and the chromosomes are each composed of
single chromatids.
B. Diploid; and the chromosomes are each composed of two
chromatids.
C. Haploid; and the chromosomes are each composed of
single chromatids.
D. Haploid; and the chromosomes are each composed of two
chromatids.
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This is a tricky one
8. A certain type of grass has a diploid chromosome number of 14.
A similar species of grass has a diploid chromosome number of
20. Hybridization between the two species results in sterile
hybrids that can, nonetheless, reproduce vegetatively (though
do not produce fertile offspring due to errors in meiosis). The
chromosome number in the somatic (non-sex) cells of those
hybrids would be
A. 17
B. 18
C. 9
D. 16
E. 20
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Ploidy
Ploidy = the number of sets of chromosomes.
Diploid organisms are those with two (di) sets (2n).
Haploid organisms are those with one set (n).
„
„
Gregor Mendel determined his peas had two sets of
alleles, one from each parent.
Human beings (except for their gametes), most
other animals, and many plants are diploid.
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Nuclear division by
mitosis or meiosis
Most cells in the eukaryote are produced by
mitosis. These are the somatic (or
vegetative) line cells (e.g., cells in the skin,
lung, muscle).
Cells that become gametes are referred to as
germ line cells. Only germ cells undergo
meiosis to produce gametes (eggs or
sperm).
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Cell Cycle review
„
„
„
„
G1 stage: GAP 1
S stage-"Synthesis"DNA replication
G2 stage: GAP 2
M stage- "mitosis"
phase
www.blc.arizona.edu/INTERACTI
VE/mitosis3.95/mitosis1.html
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What’s in a name?
Be able to define, identify, and compare
„ Chromosome versus chromatid
„ Homologous chromosomes
(maternal and paternal chromosome)
„
„
Sister chromatids versus non sister
chromatids
tetrad
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Chromsome and chromatid
http://staff.jccc.edu/pdecell/celldivision/chromoterm.html
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Chromatid vs. Chromosome
when two DNA molecules are joined together, each
molecule is called a chromatid and the two of the
molecules are called a duplicated chromosome.
When a DNA molecule(and proteins) is not attached to
another one then that single molecule of DNA is not
a chromatid but an unduplicated chromosome.
.
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[unduplicated]
Homologous chromosomes
http://www.apsu.edu/~Thomps
onJ/Anatomy
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Homologous chromosomes
http://staff.jccc.edu/pdecell/celldivision/chromoterm.html
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Gene, allele, locus
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Centromere
Pinched in region somewhere along the length
of the chromosome
„ region to which the spindle fibers attach to
the chromosome and it is in a characteristic
position that is constant for different types of
chromosomes.
„ contains a small ring of protein called a
kinetochore which is important in the
movement of chromosomes during mitosis
and meiosis.
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Mitosis review
Mitosis is the nuclear division of ordinary
somatic cells
www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html
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„
Mitosis review
http://www.apsu.edu/~ThompsonJ/
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Cytokinesis: cell division
Plant cells: cell plate forms dividing cell into two
cells
Animal cells: cleavage furrow forms in middle of
cell and pinches inward until cell divides into
two cells.
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Meiosis
Purpose:
1.
keep chromosome number constant across
the generations
2.
ensure that each gamete contains only one
member of each homologous pair
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Meiosis Overview
Two successive nuclear divisions occur:
Meiosis I (Reduction)
Meiosis II (Division).
Meiosis produces 4 haploid cells.
(Mitosis produces 2 diploid cells. )
Meiosis I reduces the ploidy level from 2n to n
(reduction) while Meiosis II divides the remaining set
of chromosomes in a mitosis-like process (division).
Most of the differences between the processes
occur during Meiosis I.
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www.ncbi.nlm.nih.gov/About/primer/genetics_cell.html
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http://www.accessexcellence.org/RC/VL
/GG/meiosis.html
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Comparison of meiosis & mitosis
[eukaryotic cells]
Homologous
chromosomes
Chromosome #
Meiosis
Mitosis
Pair until anaphase I
independent
Reduced
Identical # in
daughter cells
(haploid daughter cells)
Genetic identity
of daughter cells
New assortment +
Recombination by
crossing over
identical
DNA synthesis
Before first division
Before each
division
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Autosomal chromosomes &
Sex Chromosomes
„
„
Autosome refers to those chromosomes that
are not involved in sex determination. (e.g.,
human diploid cells have 22 pairs of
autosomes and 1 pair of sex chromosomes).
Sex chromosomes are chromosomes
involved in a major way in sex determination.
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Sex determination
Humans : two X chromosomes (XX) females X
chromosomes and a Y chromosome (XY)
males.
Not the same in other organisms e.g.,
birds the females are XY and the males are XX!
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Sex chromosomes often
lack homology
X and Y chromosomes are not strictly
homologous.
►[in humans] X chromosome is much bigger
than the Y chromosome & most of the genes
on the X chromosome do not have
corresponding genes on the Y chromosome.
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Next lecture:
Recombination:
1. Independent assortment of homologues
2. Crossing over between non-sister
chromatids during Prophase I
Meiosis has large impact on variation
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