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Transcript
Chapter 11,12,15 Cellular Basis of Reproduction and Inheritance
Introduction
300 ENDANGERED PLANTS in Hawaii
Cyanea kuhihewa
the single know plant flowered, scientists tried to promote sexual reproduction in this lone plant, the
process that involves fertilization-the union of a sperm and egg. If successful the fertilized egg divides into
two cells then 4 eventually forming an embryo then a seed. upon germination the embryo may develop into
a juvenile and later into an adult plant. Development from a fertilized egg inot a new adult organism is one
phase of an organisms life cycle –the sequence leading from the adults of one generation to the aults of the
next generation. The other phase of the life cycle is reproduction, the forming of new individuals from
preexisting ones. Reproduction involves the creation of new offspring carrying the genetic material, as DNA,
from their parents Sperm and egg carry carry one set of genetic information—one copy of the organisms
genome. The offspring inherit traits from two parents providing genetic diversity. The attempt failed and
now botanists are trying asexual reproduction , the production of offspring by a single parent resulting in
offspring geneticall identical to the parent. Cell division is at the heart of reproduction. Cells becoming
more cells for the organisms various structures and a special kind of cell division that produces the sperm
and eggs.
Asexual reproduction
single parent
pass on ALL genes
genetically identical to parent
clone
rare genetic differencesby mutation
Sexual reproduction
two parents
pass on 1 / 2 genes
unique combination of genes from both parents
greater genetic variation- offspring vary
genetically from siblings and parents
Cell theory-- Virchow all cells come from preexisting cells; ---therefore cells must be able to divide
cell division produces
*in unicellular organisms cell division is reproduction
*in multicelluar organisms cell division allows for:
growth / development
replace damaged / dead cells
cell division requires chromosome [genome all genetic information] replication.
A fertilized egg, after 6 divisions, will produce an embryo containing _____ cells
Prokaryotes-bacteria reproduce by binary fission
loop of genetic material is copied, one copy moves to the opposite end of the cell
the cell elongates as the chromosome duplication process continues
the plasma membrane grows inward dividing the cell into two daughter cells
Eukaryotic cell division-[for growth in multi-cellular organisms and to replace worn out or damaged cells, in
unicellular organisms it results in reproduction]
larger more complex chromosomes composed of genetic material + protein = chromatin
usually they are thread-like ---not a loop
when a cell prepares to divide its chromosomes coil up forming visible chromosomes
the number of chromosomes depends on the species, humans 46, dog 78
when a eukaryote prepares to divide:
chromosomes are duplicated and proteins attach as needed
each chromosome is now two identical copies of DNA called sister chromatids
they are joined by a structure called the centromere
8.4c
Cell cycle
Interphase -----> G 1 phase -----> S phase ----------> G 2 phase ----------> M phase ----------> Interphase
Interphase represents most of the cell cycle-the cell is doing its assigned tasks a time of high metabolic
activity—increases supply of proteins, creates more organelles and grows in size. Duplication of
chromosomes happens. Interphase comprises 90% of the cell cycle
1)
2)
3)
G1 phase - first growth phase
S phase - synthesis (DNA synthesized, chromosomes duplicate}
G2 phase - second growth phase {1+ nuclei and 2 centrosomes}
M phase--shortest part of the cell cycle, composed of:
1) mitosis nuclear division
2) cytokinesis, cytoplasmic division
Very accurate process; 1 error in every 200,000 divisions [yeast]
Mitosis—CREATES TWO GENETICALLY IDENTICAL CELLS
1. Prophase
nucleoli disappears
chromatin coils tightly
duplicated chromosomes –(chromatids) connected by the centromere
spindle forms from microtubules
2. Pro-metaphase
nuclear envelope fragments
microtubules reach equator and attach to centromeres and kinetochores = agitation
protein “motors” on microtubules move chromosomes to center of the cell
3. Metaphase
chromosomes line up
opposite spindle fibers attach to chromosomes; one from each pole
4. Anaphase
centromeres separate splitting sister chromatids from each other
motor proteins of the kinetochores, using ATP, walk the daughter chromosomes toward the two
poles while the cell elongates
spindle fibers shorten moving one copy of each daughter chromosome to each pole
5. Telophase
cell elongation continues
nuclei reform
nucleoli reform
chromosomes uncoil ----> chromatin
cytokinesis has begun during telophase
Cytokinesis
in animal cells
*cleavage furrow
*ring of actin myofilaments shortens
*pinch the cell in two
in plant cell
*cell plate - at midline
*forms 2 membranes
*new cell wall forms between them from materials from carried in vesicles made by the golgi
Factors affecting cell division--timing issues wound repair, versus continuous skin replacement
Anchorage dependence-a cell must often be in contact with a surface to divide
density dependent inhibition when a single layer of cells or cells touch , removed cells are
replaced, analogous to cutting your skin
cause? lack of proteins called growth factors
a protein secreted by cells that stimulate other cells to divide.
nutritional status lack of certain nutrients can prevent cells from dividing
Growth Factors
Protein signals that cells respond to. Most cells are anchored and bathed by nutrient solution from
the blood. This would include the possible presence of proteins that stimulate cell division.
The Sequential events of the cell cycle suggest there is a control system-e.g. washing machine knob
Each event seems to require a chemical stimulus.
There are checkpoints in the cell cycle with stop and go signals. The model is signal transduction
meaning binding of a messenger to an integral protein of the plasma membrane that relays a message to a
protein that performs a specific activity inside the cell.
Three major checkpoints
In G1, G2 and M internal and external signals indicate if cell processes are complete. When the
control system gets a go-ahead signal the cells enters the next phase.
In G1 if the signal is not received the cell will enter a non-dividing stage called In Go [area of intense
research because of potential impact on cancer treatments]
8.9b
cancer, Growing out of control—claims the lives of 1 out of every 5 persons in the U.S. cancer is a disease
of the cell cycle
cancer cells:
don’t respond to control mechanisms e.g. density dependent inhibition; proceed past checkpoints;
synthesize own growth hormones-external source not required.
invade other tissues
can disrupt and destroy other tissues
cells immortal--continue to divide, [normal cells divide 20-50 times]
transformation converts normal cells to cancer cells [usually destroyed by the immune system]
if the cell evades destruction it may form a tumor – abnormally growing mass of cells
benign - do not migrate--can be removed
malignant – migrates to other places
carcinomas from internal/external coverings-skin; sarcomas from support tissue-bone/muscle; leukemias
and lymphomas from blood forming tissues-bone marrow, lymph nodes.
Treatments
surgeryRadiation which damages DNA especially in cancer cells which have lost the repair mechanisms.
chemotherapy for wide spread cancers-disrupt specific steps in te cell cycle
e.g. taxol freezes mitotic spindle [found in bark of Pacific yew tree]
e.g. Vinblastin from the periwinkle plant prevents spindle from forming
effects-nausea from affect on intestinal cells, hair loss from hair follicle cells, infection from affect on immune
system.
Locations for Mitosis: growth [root tip], cell replacement [bone marrow], asexual reproduction [budding in
hydra]. All cells genetically identical to original cell.
Chromosomes: homologous pairs
same size, shape, contain the same genes [e.g. hair color, blood type]
homo---means the same
the gene for freckles is located on a particular chromosome at a specific locus
the other chromosome has a gene for freckles at the same locus
the two homologues may have different version one promoting and one that does not-they may
carry different versions of the same gene say coat color C, c and eye color B, b in mice.
The exception
X and Y chromosomes do not carry the same genes
females one homologous pair XX
males one X and one Y
XY
most genes on the X do not have counterparts on the tiny Y
called sex chromosomes
Gametes have a single set of chromosomes--haploid
Human body cells [autosomes] have two sets of chromosomes--diploid
Life cycle-------- of sexually reproducing organisms
zygote--diploid
(46 chromosomes)
fertilization
mitosis
growth
development
repair
cells--diploid
(46 chromosomes)
sperm--haploid
(23 chromosomes)
ovum --haploid
(23 chromosomes)
meiosis-reduces chromosome number by 1/2
Meiosis is a special type of cell division reduces chromosome number by half
C
B
___________________
C
B
___________________
can produce 2 different gametes
c
b
___________________
c
b
___________________
Meiosis consists of two cell divisions producing 4 unique cells [gametes]
crossing over
homologous chromosomes pair up, synapsis, and exchange genetic material.
C
B
___________________
C
b
___________________
can change this to 4 different gametes
c
B
___________________
c
b
___________________
Independent orientation of chromosomes [independent assortment]
Be able to compare mitosis and meiosis!
fertilization joining of sperm and egg returns diploid number
Random genetic recombination of gametes
Three sources of genetic variability
crossing over
independent orientation of chromosomes-metaphase l
random fertilization
Errors in meiosis
Karyotype a photograph of an organisms chromosomes.
Humans 23 pairs of chromosomes, last pair will not match for males XY.
Blood obtained, centrifuged, cells separated, hypotonic solution solution added, red blood cells
burst-white blood cells swell but don’t burst, centrifuged to remove red cell material, white blood
cells preserved and stained, photographed, chromosomes arranged by size and shape.
1.
Non-disjunction-chromosomes do not correctly separate in anaphase. Results in a cell
missing or containing chromosomes n + 1, n – 1.
the embryo form from this cell has too many chromosomes or is missing chromosomes.
2n + 1; 2n – 1
Why? meiosis starts in the ove before birth and finishes when the ova is fertilized…maybe the
restarting process is not fully activated----Downs syndrome is 2n + 1 an extra chromosome #21
XXY
XYY
XXX
XO
1/700 children
kleinfelter syndrome—male, sterile, small testes, possible female characteristics
normal male
XXXY, XXYY, etc. possible retardation
normal female
Turner syndrome—female, sterile, little secondary sex characteristics
Barr Bodies
in females one X chromosome is inactivated--visible as a barr body
therefore 1 / 2 of a female’s cells use one X; the other 1 / 2 use the other Mosaic pattern
Pataus Syndrome
1 / 5000
2n + 13
eye, brain, circulatory, cleft palate
Edwards Syndrome
1 / 10,000
2n + 18
<:
every system
die first year
Cri du Chat
part of # 5 missing
Aneuploidy---incorrect number of chromosomes
Alterations of chromosomes
single chromosome alterations
deletion--missing part of the chromosome
duplication--the missing part from one chromosome joins with the homologous partner
inversion--part breaks off then reattaches backwards
two non-homologous chromosomes
reciprocal translocation-chronic myelogenous leukemia
between #9 and #22 activated cancer causing gene.