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Transcript of CHAPTER 8 The Cellular Basis of Reproduction and Inheritance Sexual reproduction mitosis asexual...
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CHAPTER 8
The Cellular Basis of Reproduction and InheritanceSexual
reproduction
mitosis
asexual reproducti
on
meiosis
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Prokaryotic vs. Eukaryotic• Binary fission• Cell divides in half• Chromosome
replicates & attaches to plasma membrane
• 2 copies will be separated by growth that occurs between them
• 2 identical cells form
• Genes grouped into chromosomes (long thread-like structures)
• Cell duplicates chromosomes as well as genes
• Mitosis occurs• Duplicated
chromosomes are evenly distributed into 2 daughter nuclei
• cytokinesis
Sect 8.3
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Chromosomes
•Consists of a long DNA molecule (represents thousands of genes)
•Also consists of proteins (structure, helps control gene activity)
Sect 8.4
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• This DNA-protein complex is chromatin• Chromatin is organized into a long, thin fiber• Fiber is coiled & folded to form the chromosome• Gene – a unit of information on a chromosome
- consists of DNA- can be passed along to offspring
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•All cells in the body (somatic) have the same # of chromosomes (46)
•Except for sperm & eggs (sex cells – 23)
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•When chromosomes replicate, they form 2 identical structures called sister chromatids (joined by a centromere)
•When the sister chromatids separate during mitosis, each goes into a daughter cell
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Cell Cycle (summary)
•Cell doubles its amount of cytoplasm including organelles
•DNA is duplicated•Nucleus & its contents divide
by mitosis•Cytoplasm is divided
between 2 daughter cells
Sect 8.5
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Cell Cycle (Interphase)• Lasts 90% of
total time for cell cycle
• Divided into 3 phases:
- G1 Phase (1st gap) period of interphase before DNA synthesis begins (growth in size, proteins, organelles)
- S Phase (synthesis) when DNA synthesized
- G2 Phase (second gap) period after DNA synthesis begins but before mitosis begins (proteins synthesized essential to cell division)
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Cell Cycle (M Phase)
•10% of cell life•Mitosis – nucleus & contents
divide •Cytokinesis – cytoplasm
divides which generates 2 daughter cells
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Cell Cycle (Phases of Mitosis)
•Prophase•Prometaphase•Metaphase•Anaphase•Telophase/Cytokinesis
Sect 8.6
p. 130-131
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Prophase• Chromatin
tightens & thickens (chromosomes now visible)
• Each duplicated chromosome is seen as 2 identical sister chromatids joined by a centromere
•Nucleus disappears
•Microtubules form a radial array called an aster around each centriole
•Mitotic spindle forms
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Prometaphase • Nuclear envelope disappears & spindle enters nucleus
• Bundles of microtubules extend from pole to equator
• Centromeres have kinetochores to which kinetochore fibers are attached
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Metaphase
•Centriole pairs are now at opposite poles
•Chromosomes line up on the metaphase plate (a plane between the 2 poles)
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Anaphase• Paired
centromere of each chromosome moves apart-sister chromatids are now free of each other-each chromatid is now a chromosome
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•Spindle moves the chromosomes to opposite poles
•Poles move farther apart•Each pole now has a
complete set of chromosomes
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Telophase•Polar fibers
elongate•Nuclear
envelopes are formed from earlier fragments from the parent cell
•Nucleolus reappears•Mitosis is complete
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Cytokinesis(animals – cleavage)
•Shallow groove in cell surface near old metaphase plate (called cleavage furrow)
•Contractile ring of microfilaments is found on cytoplasm side of furrow
-ring contracts & shrinks in diameter
-Cleavage furrow deepens until parent cell pinches in two
Sect 8.7
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Cytokinesis(plants – no cleavage
furrow)•Cell plate forms across
midline of parent cell•Double membrane is formed•Fusion of each of these 2
membranes w/plasma membrane results in the formation of 2 daughter cells
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What affects mitosis?
Normal Cell Division – 3 factors:
Anchorage Dependent – cells must be “anchored” to a solid surface to divide; keeps cells separated from their normal surroundings from dividing inappropriately
Sect 8.8
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Density-Dependent Inhibition – rate of cell division decreases as cell population becomes denser
Growth Factors – proteins secreted by certain body (somatic) cells that stimulate other cells to divide
p. 133
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Cell-Cycle Control Systems
•It is a cyclically operating set of proteins (mostly growth factors) in the cell that triggers & coordinates major events in the cell cycle.
•Major checkpoints in G1, G2, and M:
- G1 checkpoint seems to be most critical in many cells (gives go-ahead to start cell-cycle & divide, non-dividing cells are stuck at G1
checkpoint called Go)
Sect 8.9
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-G2 checkpoint gives go-ahead to start M phase
-M checkpoint go-ahead signals that the proper attachment of the spindle fibers to the chromosomes & prompts the separation of the sister chromatids
-What is signal transduction?* Protein that receives signals for specific activities
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Uncontrolled Cell Growth- can produce excessive growth resulting in an abnormal mass called a tumor• Benign =
abnormal mass of normal cells that normally remain at their original site
• can usually be removed by surgery
• Malignant = mass of cancer cells that can spread beyond their original site to neighboring cells (growth) or other sites of the body (metastasis – circulatory system)
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Cancer cells do not have a properly functioning cell-cycle.
• Carcinomas – cancers of the external & internal linings of body (skin, linings of intestines)
• Sarcomas – cancers of tissues that support body (bone, muscle)
• Leukemias & Lymphomas – cancer of blood-forming tissue (bone marrow, spleen, lymph nodes)
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Treatment for Cancer• In radiation
therapy, cancer cells are most likely dividing at any given time & will destroy cells by disrupting cell division w/out injuring normal cells
• Chemotherapy uses the same strategy as radiation therapy but uses chemicals instead
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Sexual & Asexual Reproduction
• When offspring results from 2 parents
• Offspring has a unique combination of genes inherited from BOTH parents
• When an individual inherits all its genes from a SINGLE parent
• Consists of simple division or budding
Sect 8.11
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Sexual Life Cycle (human)
•Each somatic cell = 46 chromosomes
•Chromosomes differ from each other in size, position of centromere, staining pattern
•Matched in pairs (this creates a karyotype)
Sect 8.12
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•Chromosomes that make up a pair are called homologous chromosomes
- same size & have same centromere position
- each carries genes controlling same inherited trait but possibly different versions
-genes for a certain trait are located in a particular place - locus
blue
green
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•23rd pair of chromosomes is the sex chromosomes
- XY for males
- XX for females
•All other chromosomes are called autosomes
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Chromosome Numbers
•Humans inherit 2 sets - maternal = 23 - paternal = 23•Cells containing 2 sets are
diploid or 2N•Cells containing 1 set are
haploid or 1N
Sect 8.13
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•Gametes are haploid cells
- they are reproductive cells, either sperm or egg
•Each sperm or egg has single set of 22 autosomes plus 1 sex chromosome•Fertilization occurs when egg & sperm unite & create a zygote
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•Production of gametes requires a special type of division
- use reduction division called meiosis
- reduces chromosome number by half
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Meiotic Cell Division
Meiosis I - Prophase I - Metaphase I - Anaphase I - Telophase I/
Cytokinesis
Meiosis II - Prophase II - Metaphase II - Anaphase II - Telophase II/
Cytokinesis
Sect 8.14
p. 138-139
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Meiosis I
• Produces haploid gametes in diploid organisms
(Prophase I)
•Homologous chromosomes come together as pairs
- each is made of 4 chromatids
- each forms a tetrad
- 90% of meiotic cell division
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- crossing over of genetic material can occur (segments of non-sister chromatids can exchange places)
- spindle forms
- nuclear envelope & nucleolus disappear
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(Metaphase I)
•Tetrads line up on the metaphase plate
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(Anaphase I)•Homologous pairs separate & go to opposite poles (only tetrad splits)
(Telophase I/ Cytokinesis)•Cytoplasm divides making 2 daughter cells•Interkinesis occurs (rest time)
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Meiosis II
(Metaphase II)
•Chromosomes line up on the metaphase plate
(Prophase II)Spindle moves chromosomes toward the equator
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(Anaphase II)
•Centromeres of sister chromatids separate
•Individual chromosomes move to poles
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(Telophase II/ Cytokinesis)•Nuclear envelope reforms•4 daughter cells are made (each has ½ the number of chromosomes of parent)
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Comparing Mitosis & Meiosisp. 140
• Behavior of chromosomes is same
• 2 daughter cells that are each 2N
• Behavior of chromosomes is same
• 4 daughter cells that are each N
• Very different than mitosis because of tetrad
Sect 8.15
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Genetic Variation
•Independent Assortment•Random Fertilization•Crossing Over
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Independent Assortment
•Orientation of homologous pairs relative to the 2 poles is random (there are 2 possibilities)
•The first meiotic division results in independent assortment of maternal and paternal chromosomes into daughter cells
Sect 8.16
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•In humans, the number of combinations of maternal or paternal chromosomes is 223 = 8 million
•There are 2N possible combinations where N is the haploid number
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Random Fertilization
•An egg cell represents 8 million different possibilities
•A sperm cell represents 8 million different possibilities
•A zygote will have 64 trillion diploid combinations
Sect 8.17
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Crossing Over
• Identical regions of chromatids are exchanged
- results in a change in genetic material
- this is known as genetic recombination
• Produces combinations different from those originally inherited
Sect 8.18