Transcript CELL DIVISION

CELL DIVISION
Mitosis
Why do cells divide?
• Growth
• Repair
• Replace
• Reproduction
Mitosis
• Interphase
• Growth
• Cell activities (make
•
•
•
•
proteins, transport
nutrients,eliminate waste)
Nucleus is visible
Genetic material is called
chromatin (long thin strands)
Replication of DNA
Sister chromatids joined by
centromere
Mitosis
• Prophase
• Chromatin coils into chromosomes
• Nuclear membrane disappears
• Centrioles migrate to poles
• Spindle fibers form
Mitosis
• Metaphase
• Chromosomes (composed of sister chromatids) align at the
equator, that are attached to spindle fibres
Mitosis
• Anaphase
• Centromeres divide and sister chromatids
(chromosomes) separate and move to opposite poles
Mitosis
• Telophase
• New nuclear membranes
• Spindle disappears
• Chromosomes unwind
Cytokinesis
• Cytoplasm is divided in half
• cleavage furrow (animal)
• cell plate (plant)
Animal Cells
Plant Cells
Animation and Real Footage
• http://www.youtube.com/watch?v=VlN7K1-9QB0
• http://www.youtube.com/watch?v=rgLJrvoX_qo&feature=related
• http://www.youtube.com/watch?v=Q6ucKWIIFmg
CELL DIVISION
Meiosis
The need for meiosis (do not copy)
• During mitosis, the complete set of chromosomes is duplicated. Every new cell
produced by mitosis receives a full set of genes that control its development.
• Sexual reproduction, introduces a new problem. Suppose that an egg nucleus
contains one full set of chromosomes. Let the symbol N represent the number of
chromosomes in this set. Then the sperm nucleus will bring another set, another
N.
• EGG
• N
+
+
Sperm ------------------ ZYGOTE
N
---------------- 2N
• When the egg and sperm unite, the zygote will contain 2N – a double set of
chromosomes. Suppose the process of mitosis were to maintain this double set of
chromosome in every cell of the embryo and eventually the adult. At the next
fertilization, if the number of chromosomes doubled again then
• 2N
+
And again
• 4N
+
2N ----------------4N
4N-----------------8N
• You see that eventually there would be too many chromosomes for the space in
the nucleus.
Meiosis
• Is a special kind of nuclear duplication of sex cells
• The double set of chromosomes (2N or diploid number) is
reduced to a single set. The number of chromosomes in
the single set is called the HAPLOID NUMBER (N).
• Both the egg and sperm contain the haploid number. In
humans the diploid number is 46 the haploid number is 23
(46/2= 23). Egg and sperm cells contain 23
chromosomes.
Two Types of Cell Division
• Handout
ACTIVITY Cut & Paste Meiosis
Things you need to know before you begin
- Meiosis resembles mitosis, both processes begin with chromosomes
duplicating, thickening and shortening
- There is a difference in the way the duplicated chromosomes line up in
the middle of the cell. The chromosomes line up in matching pairs. Some
chromosomes may break and exchange parts with their partners
- A second cell division immediately follows the first. Result 4 Haploid cells
which are formed from the one original cell
Label Centromere, nuclear membrane, sister chromatids, tetrad,
Crossing Over, cleavage furrow, spindle fibres, Prophase I & II,
Metaphase I & II, Anaphase I & II, Telophase I & II, Cytokinesis,
4 haploid cells
Sexual Reproduction
• Genetic diversity is created through 3 process:
• Fertilization
• Crossing over
• Random Assortment
The family of Sissy Spacek and Jack Fisk exhibits genetic variation.
Sexual reproduction produces variation in the gametes and unique
combinations of genes in the offspring.
Fertilization
• Given the number of different
individuals in the population,
the number of different
combinations of parents is
vast.
• Any of a number of different
gametes can fuse to make a
zygote and each one would
be unique.
Crossing Over
• Prophase I of meiosis
• Homologous
chromosomes form tetrads
• During synapsis pieces of
the chromosomes are
exchanged
• Maternal and paternal
genes are carried on the
same chromosome now
Random Assortment
• There are numerous patterns of alignment during
Metaphase I
• Maternal and paternal homologues segregate randomly
Meiosis
• Reproduction (plants, fungi,
animals)
• Produces gametes (haploid)
• Fertilization forms a zygote
(diploid)
• DNA replicated once, cell
divides twice
•
http://www.youtube.com/watch?v=AgEqWPyO8z0&feature=r
elated
Meiosis
• FEMALES
• Begins during 3-5th month of fetal development
• Continues from puberty to menopause
• One large egg cell and 3 polar bodies
Meiosis
• MALES
• Begins before birth
• From puberty until death or damage
• Temperature and age dependent
Determining Sex/Gender
• All eggs and sperm carry 23 chromosomes (human)
• Autosomes are #1-22
• Sex chromosome is #23
• Eggs contain X
• Sperm may contain either X or Y
CELL DIVISION
Atypical or Abnormal Cell Division
Mitosis Gone Awry
• Mutations in the genes
that control cell division
trigger an abnormal cell
cycle.
• Accumulation of these
mutations due to
environmental stimuli
leads to tumour growth.
• Carcinogens, radiation
and viruses can all cause
mutations.
http://www.youtube.com/watch?NR=1&v=Hm03rCUODqg
Breast cancer cells dividing
(3 days time lapse)
Mutations in somatic
cells aren’t passed to
offspring
Damage to Chromosome Structure
• Large scale mutations that damage chromosome structure can
occur when something unusual happens during crossing over.
Translocation – the transfer of a chromosome segment to a nonhomologous chromosome.
Deletion - occurs when a chromosome segment breaks off,
resulting in the loss of some genes
Duplication – occurs when part of a chromosome is repeated
Inversion – occurs when a piece of a chromosome is rotated so
that the order of genes in the segment is reversed.
Atypical Meiosis
• NONDISJUNCTION – the uneven separation of
homologous chromosomes during Anaphase.
Mutations in gametes
• Mutations in meiosis are inherited by offspring though no
disorder was evident in the parent
• By age 42, 90% of a woman’s eggs are chromosomally
abnormal. Thus, at age eighteen, 1:2,000 live births
results in Down Syndrome. By age 42 that rises to 1:25
Trisomy 21
• Down Syndrome – there is an extra chromosome in either
the egg or sperm making 47 in the zygote
Genetic Screening
• Amniocentesis –
withdraw fluid and
cells from the
amniotic sac
surrounding the
fetus to look at
chromosomal
abnormalities
http://video.about.com/pregnancy/Am
niocentesis.htm
Trisomy 8,9,13,16,18
• http://www.youtube.com/watch?v=-QJF0Cs4f9s
• March is Trisomy Awareness month. I photographed this
series of portraits at the SOFT (Support for Families with
Trisomy 18, 13 and Related Disorders) conference in
Roanoke, Virginia during July 2009. I am trying to raise
awareness that while only 10% of these kids survive their
first year the ones that do live a rich life. Expectant
parents are often told that Trisomy is incompatible with life
and I am trying to share their unique beauty through these
digital images. These children and young adults do not
pose for photographs but can be captured being
themselves, living in the moment. Most are non-verbal so
I see it as an honor to help tell their stories visually.
• http://www.youtube.com/watch?v=-u2nbfgpP3U
Activity
• Quick Lab pg. 122 (construct and Analyze Karyotypes
• Homework pg. 120 #1~3