Ch 12 The Cell Cycle & Mitosis

Ch 12 The Cell Cycle & Mitosis
What did the brother cell say when the sister cell stepped on him? Mitosis.

Cells come from ________________ cells
This statement tells us that cells reproduce and the way they do this is through cell ________________ (p.218 Figure 12.1). Roles in Life: _________________ Amoeba: divides and forms a duplicate Plants: some can divide and form offspring Sexual Reproduction: organisms develop from a single cell (zygote) Renewal and Repair Dying, ________, or torn cells. Cell Cycle: life of a cell from the time it is formed from a dividing _________ cell until its own division into two cells. Cell division is ________ of the cell cycle PRE-EXISTING DIVISION REPRODUCTION WORN PARENT PART

Cell Division: results in genetically ________________ daughter cells
Organization of Genetic Material (______) __________: the entire amount of genetic material (DNA) Length of DNA is very large (2 m of DNA in human cells: __________ greater than a cell’s diameter). This DNA must be copied _________ division. The reason DNA replication is not a problem is because DNA is packed into chromosomes made of ________________ (DNA wrapped around ___________) Each species has a certain number of _________________ in each cell nucleus. IDENTICAL DNA GENOME 250,000 x BEFORE CHROMATIN PROTEINS CHROMOSOMES

Ex: Humans have ___ chromosomes (2 sets of 23, one from each parent).
Two types of cells: ___________ (body) cells: all cells that are not reproductive (sex) cells. Ex: Humans have ___ chromosomes (2 sets of 23, one from each parent). ____________ (sex/reproductive cells): sperm and egg cells Ex. Human gametes have half as many chromosomes as somatic cells: one set of ______ chromosomes. SOMATIC 46 GAMETES 23

Distribution of Chromosomes During Cell Division
When not in division, each chromosome is in the form of chromatin, but ________________ (coils) to chromosomes after duplication so they are __________. Each duplicated chromosome has two ___________ chromatids Two chromatids, each containing an identical DNA molecule are attached at the ________________. CONDENSES VISIBLE SISTER CENTROMERE

In cell division, the two sister ________________separate into two nuclei, one at each end of the cell. Once the sister chromatids separate, they are considered individual __________________. Each nucleus has a group of chromosomes ________________to the original. Mitosis: division of the _____________ (chromosomes split into 2 identical sets) Cytokinesis: division of the ________________ (division of the two nuclei into two cells) Example: ______ (46 chromosomes): 23 chromosomes (______) chromosomes (______) Mitosis and ________________produce the trillions of somatic cells that make up human bodies and continue to generate cells. Meiosis: yields _________________ daughter cells that have only one set of chromosomes. Only occurs with __________. This will be covered in Ch. 13. CHROMATIDS CHROMOSOMES IDENTICAL NUCLEUS CYTOPLASM BABY MOM DAD CYTOKINESIS NON-IDENTICAL GAMETES

Phases of the Cell Cycle
________________ (M) Phase (when division occurs)- ___________ part of the cell cycle that includes: _________ ______________. cell cycle animation MITOTIC SHORTEST MITOSIS CYTOKINESIS

90 Interphase (in ____________ cell divisions)- accounts for ____% of the cell cycle Where the cell _________ and copies its chromosomes to prepare for division Three Subphases: ____ Phase (“first gap)- protein and ________________ (mitochondria and chloroplast) synthesis (double cell size) S Phase (“________________”)-___________________ are duplicated (DNA synthesis only in S phase) ___ Phase (second gap”)- continued growth Sequence (remember): ________________ (G1, S, G2), M phase mitosis: prophase, ___________________, metaphase, anaphase, telophase cytokinesis BETWEEN GROWS G1 ORGANELLE SYNTHESIS CHROMOSOMES G2 INTERPHASE PROMETAPHASE

Consists of fibers (__________________ and proteins).
Mitotic Spindle Involved in many events of mitosis and begins to form in the ________________ during prophase. Consists of fibers (__________________ and proteins). The spindle microtubles lengthen by including more subunits of ________________. CYTOPLASM MICROTUBULES TUBULIN

Mitotic Spindle Assembly:
Starts at the ________________ centrosome- a nonmembranous organelle that organizing the cell’s microtubules during the cell cycle In animal cells, two ________________ are located at the center of the centrosome but are not essential to cell division. Ex: ________ don’t have centrioles ________________is when the centrosome replicates to form two which stay together near the nucleus. The two move apart during prophase and __________________ as spindle microtubules grow from them. At the end of prometaphase, the two centrosomes are on ____________ ends of the cell. An _________ which looks like a sun burst of microtubules from each centrosome. CENTROSOME CENTRIOLES PLANTS INTERPHASE PROMETAPHASE OPPOSITE ASTER

Chromosomes Each chromatid of a chromosome has a ________________-a structure of proteins that appear at specific sections of chromosomes at the centromere. Kinetochores are where microtubules connect to pull sister ________________ apart The centrosome’s two kinetochores face in ____________ directions. During prometaphase, some of the spindle microtubules attach and are called kinetochore microtubules. The next event is like a ________________ that ends in a draw: the chromosomes move and finally stop when the centromeres of all the duplicated chromosomes are on a plane __________ between the spindle’s two poles. This plane is the metaphase _______. At this time there are some microtubules that are not attached to kinetochores but overlap and interact with other _______________________ microtubles. KINETOCHORE CHROMATIDS OPPOSITE TUG OF WAR MIDWAY PLANE NONKINETOCHORE

Moving apart Starts when the proteins holding the sister chromatids become ________________ allowing the sister chromatids to become separate chromosomes. These chromatids will move toward opposite sides of the cell. The region of overlap between the microtubules is reduced as ATP is used to push the microtubules apart. This ________________ the cell. At the end of anaphase, duplicate groups of chromosomes arrive at ____________ ends of the now longer parent cell. During telophase, nuclei reform and cytokinesis begins and the spindle disassembles. INACTIVE ELONGATES OPPOSITE

Summary of the Cell Cycle mitosis animation Interphase
Nuclear envelope is ________________ The nucleus has at least one ________________ Two centrosomes have formed and will be next to each other (animal cells will have ______________). In the nucleus, ________________ is seen PRESENT NUCLEOLI CENTRIOLES CHROMATIN

Chromatin has condensed into __________________.
Prophase Chromatin has condensed into __________________. Duplicated chromosomes appear as identical sister chromatids joined at _________________. Nucleoli disappear. Mitotic spindle forms as centrosomes move apart. as microtubules emerge from the centrosomes, _________ can also be seen. CHROMOSOMES CENTROMERES ASTERS

Nuclear envelope ___________ down.
Prometaphase Nuclear envelope ___________ down. Chromosomes become more ________________. Microtubules from the mitotic spindle _________ even more. Each sister chromatid has a ________________ located at the centromere. Kinetochore microtubule: ________ chromosomes Nonkinetochore microtubules interact with other nonkinetochore microtubules (from _____________ side). BREAKS CONDENSED EXTEND KINETOCHORE MOVE OPPOSITE

Metaphase (longest stage of mitosis)
Centrosomes are at ________________ poles of cell Chromosomes line up in the middle of the cell (metaphase __________) The kinetochore of sister chromatids are connected to microtubules from the opposite pole. OPPOSITE PLANE

Anaphase- shortest stage of mitosis
____________ protein cleaved allowing sister chromatids to move apart allowing each to become a separate chromosome. The two chromosomes move toward opposite ends of the cell as kinetochore microtubules ___________. The nonkinetochore microtubules ____________ which elongate the cell At the end, the two ends of the cell have an _________ amount of complete chromosomes. COHESION SHORTEN LENGTHEN EQUAL

______ nuclei form in the cell.
Telophase ______ nuclei form in the cell. Nuclear envelopes form from parent cell’s nuclear envelope ____________. ________________ reappear Chromosomes become less condense (________________) Mitosis is complete (2 complete, ___________ nuclei) TWO FRAGMENTS NUCLEOLI CHROMATIN IDENTICAL

Cytokinesis Division of cytoplasm usually starts in late _____________. Two ________________ cells appear shortly after mitosis ends. Animal cells form a cleavage ___________ which pinches the cell (cytoplasm) in two. Plant cells form a ________________ which divides the cell (cytoplasm) in two. TELOPHASE DAUGHTER FURROW PLATE

Cleavage Furrow (animals)
Cytokinesis in Detail Cleavage Furrow (animals) First sign is a shallow groove in the cell surface near the old metaphase plate. It deepens until the parent cell is pinched in two producing two separated cells with their own organelles, etc.

Cell Plate (plants) Cell wall materials carried in the ___________ collect in the cell plate as it grows. The cell plate grows until its membrane _______ with the plasma membrane along the perimeter of the cell. Two daughter cells result, each with its own plasma membrane and cell ______. VESICLES FUSES WALL

Binary Fission ________________ reproduction of single-celled eukaryotes, such as the amoeba includes mitosis and occurs by a type of cell division called binary fission, meaning "division in half.' Prokaryotes (bacteria and archaea) also reproduce by binary fission, but the prokaryotic process does not involve ________________. ASEXUAL MITOSIS

Evolution of Mitosis Hypothesis: mitosis had its origins in ________________ prokaryotic mechanisms of cell reproduction. Support: Some of the proteins involved in bacterial binary fission are related to eukaryotic ________________ that function in mitosis. As eukaryotes evolved, with larger genomes and nuclear envelopes, binary fission, seen today in bacteria, somehow led to ________________. Possible hypothesis for the stepwise evolution of mitosis. Figure p.237 SIMPLER PROTEINS MITOSIS

What controls the cell cycle?
Cell Cycle is controlled by specific ________________ molecules in the cytoplasm. Experiment: Two cells in different phases of the cell cycle were fused to form a single cell with two nuclei. If one of the original cells was in the S phase and the other was in G1, the G1 nucleus immediately entered the ___ phase Similarly, if a cell undergoing mitosis (M phase) was fused with another cell in any stage of its cell cycle, even G1, the second nucleus immediately entered ___________, with condensation of the chromatin and formation of a mitotic spindle SIGNALING S MITOSIS

Cell Cycle Control System
Definition: a ________________ operating set of molecules in the cell that both triggers and coordinates key events in the cell cycle. Checkpoint- a control point where stop and go-ahead signals regulate the cycle. Animal cells usually have built-in stop signals that ________ the cell cycle at checkpoints until overridden by go-ahead signals. Signals report whether cellular processes that should have occurred have occurred and whether or not the cell cycle should ________________. Three major ________________ are found in the G1,G2, and M phases CYCLICALLY PAUSE PROCEED CHECKPOINTS

For many cells, the G1 checkpoint ("_______________ point") in mammalian cells, seems to be the most important: if a cell receives a go-ahead signal at the G1 checkpoint, it will usually ________ the cell cycle. If a go-ahead signal is not given, it will exit the cycle, switching into a ________________ state called the G0 (G ZERO) phase. (most cells in G0 phase). Example: Think a ____________ machine. Timing device: the cell cycle control system works on its own, according to a built-in clock. Internal and External ______________: Washers have an internal sensor that detects when the water is present and external adjustment such as pressing the start button. RESTRICTION FINISH NONDIVIDING WASHING REGULATION

______________________ molecules: Protein Kinases and Cyclins
Protein kinases- enzymes that activate or inactivate other proteins by _______________________ them Protein kinases- give the go-ahead signals at the G1 and G2 ________________. Many kinases that drive the cell cycle are present at a ________________ concentration in the growing cell, but are usually in an ___________ form. To be active, such a kinase must be attached to a ________________ (gets its name from its cyclically fluctuating concentration) CELL CYCLE CONTROL PHOSPHORYLATING CHECKPOINTS CONSTANT INACTIVE CYCLIN

Because of this requirement, these kinases are called cyclin-dependent kinases, or Cdks. The activity of a Cdk rises and falls with changes in the __________________ of its cyclin partner. Figure 12.16a shows the fluctuating activity of MPF, the cyclin-Cdk complex that was discovered first (in frog eggs). Peaks of MPF activity correspond to peaks of __________ concentration The cyc1in level rises during the S and G1 phases The initials MPF stand for "________________ -promoting factor”; but we can think of MPF as "M-phase-promoting factor” because it triggers cell’s passage through G2 checkpoint to M phase. CONCENTRATION CYCLIN MATURATION

Internal and External Signals
_______________ Signal at the M phase checkpoint: __________________ In ______________, sister chromatids do not _______________ until all the chromosomes are properly attached to the spindle at the metaphase plate. It is the __________________ that send a signal that delays anaphase. When the kinetochores of all chromosomes are ______________, the sister chromatids can _____________. This allows daughter cells to have an ____________ amount of chromosomes. INTERNAL ANAPHASE ANAPHASE SEPARATE KINETOCHORES ATTACHED SEPARATE EQUAL

_______________ Factors that limit cell division
Cells will fail to _____________ if an essential nutrient is left out of the culture. ______________ factors are needed for division. Growth factors are ______________ released by cells that stimulate cell division. Platelet-derived growth factor (______) p. 231 Figure 12.17 Made by blood cells called ________________. Demonstrates that PDGF is _____________ for the division of fibroblasts in culture. PDGF sends a signal that allows cells to pass ______ checkpoint to divide. EXTERNAL DIVIDE GROWTH PROTEINS PDGF PLATELETS REQUIRED G1

Density-dependent _____________ (effect of an external physical factor)
Phenomena where crowded cells stop ____________ (p. 232: Figure 12.18a) Cells normally divide until they form a __________ layer on the surface of the container then they ________ dividing. If cells are __________, the cells around the empty space __________ until the space is filled. It was first thought that ____________ contact sent a signal to stop division but growth factors has a larger effect: When a cell population reaches a certain ____________, the nutrients available are insufficient so cell division stops. Anchorage dependence- to divide, cells must be ____________ to a (stable) surface such as a dish or extracellular matrix of a tissue. INHIBITION DIVIDING SINGLE STOP REMOVED DIVIDE PHYSICAL DENSITY ATTACHED

Loss of Cell Cycle Control in Cancer Cells
Cancer cells do _______ follow the regulations/signals like normal cells and divide excessively and invade other tissues. Cancer cells lack ____________________________________, anchorage dependence, and do not stop dividing when growth factors are depleted. Example: p. 233 Figure 12.19 Hypotheses why: Cancer cells do not need growth factors. Cancer cells make their own growth factors. Cancer cells can display growth factor’s signal despite the lack of growth factors. Abnormal cell cycle control system. (more in Ch. 19) NOT DENSITY-DEPENDENT INHIBITION

Other differences between normal and cancer cells
When/if cancer cells stop division, it is ____________ instead of at checkpoints. Cancer cells can divide _______________ if they have a continual supply of nutrients. Ex. HeLa cells RANDOM INDEFINITELY

Behavior of Cancer Cells
Transformation (change in DNA) occurs when a single cell in a tissue ______________ from a normal cell to a cancer cell. The __________ system can destroy it but if the cancer cell avoids destruction, it can continue to grow and form a tumor- a mass of abnormal cells within a “normal” tissue. ________________ tumor- abnormal cells remain at the original site No serious problems and can be removed by surgery. _______________ tumor- abnormal cells invasive enough to impair the functions of one or more organs. Someone with a malignant tumor is said to have cancer. TRANSFORMS IMMUNE BENIGN MALIGNANT

Malignant tumors: may have unusual numbers of ___________________ ________________ may be disabled- may not function in a constructive way May lose or destroy attachments to neighboring cells and the ECM to spread into nearby tissues. Can also secrete molecules that cause ___________________to grow toward the tumor. Tumor cells can separate and enter the blood vessels to travel to other parts of the body where they can form a new tumor. ________________- spread of cancer cells to locations away form original site. CHROMOSOMES METABOLISM BLOOD VESSELS METASTASIS

Treatment: Localized tumors may be treated with high-energy _________________ Radiation damages _______ in cancer cells much more than normal cells because cancer cells have lost the ability to repair such damage. ____________________- drugs toxic to actively dividing cells are given through the circulatory system to treat suspected metastatic tumors. Chemotherapeutic drugs interfere with steps of the cell cycle Example: Taxol freezes the mitotic spindle which stops actively dividing cells from going beyond metaphase. Side effects of chemotherapy are from the drug’s effects on normal cells. Nausea is caused by effects on intestinal cells, hair loss on follicle cells, and increased susceptibility to infection on immune system cells. RADIATION DNA CHEMOTHERAPY

Chapter 13- Meiosis and Sexual Life Cycles

Introduction Heredity or _________________- transmission of traits from one generation to the next Heredity passes down inherited similarities and genetic _________________. _________________- study of heredity and hereditary variation. INHERITANCE VARIATION GENETICS

Acquisition of Genes Parents pass down coded information in the form of _________ to their offspring. It is the genes that account for family ______________ such as eye color, freckles, etc. Our genes program the specific __________ that emerge as we develop from fertilized eggs into adults. In order to pass down hereditary traits, ________ must first be replicated. In animals, ___________ (reproductive cells) are what pass genes from one generation to the next. _________________: the uniting of male and female gametes (sperm and egg) which passes genes of both parents to the ____________. GENES SIMILARITIES TRAITS DNA GAMETES FERTILIZATION OFFSPRING

_________________ consist of a single long DNA coiled with proteins.
__________ genes are located on a chromosome ________: a gene’s specific location along the chromosome Asexual Reproduction (p. 239 fig 13.2) Definition: organisms produce offspring that are _________________to them (all the genes are passed). Offspring are all identical: ___________. Example: Hydra- can reproduce by budding (_________) CHROMOSOMES MANY LOCUS IDENTICAL CLONES MITOSIS

Sexual Reproduction Definition: two parents give rise to offspring that have unique _________________ of genes inherited from the parents. Offspring are genetically _________________from siblings and parents. Allows genetic _____________. Why different than asexual reproduction? Behavior of _________________ during the gamete life cycle. COMBINATIONS DIFFERENT VARIATION CHROMOSOMES

BIRTH KARYOTYPE PAIRS HOMOLOGOUS SIMILAR TRAIT SAME AMNIOCENTESIS
Sexual Life Cycles Life cycle- generation to generation occurrences in the reproductive history of an organism from _______________ to having its own offspring. _________________- display of 46 human chromosomes from a single cell in mitosis. Chromosomes are arranged in __________, according to size and structure. ___________________ chromosomes (_________________): the two chromosomes have the same length, centromere position, staining pattern. Both carry genes that control the same ____________. Ex. Eye color gene exists at the __________ locus as on the other chromosome (genes may not be identical i.e. freckles) Karyotyping can be done using cells collected by chorionic villus (placental tissue) sampling or ____________________ for pre-natal diagnosis of chromosome _________________. Used to _______ for chromosome abnormalities and genetic disorders Controversy…. BIRTH KARYOTYPE PAIRS HOMOLOGOUS SIMILAR TRAIT SAME AMNIOCENTESIS ABNORMALITIES TEST

Sex chromosomes- X and Y chromosomes determine an individual’s _____
Sex chromosomes- X and Y chromosomes determine an individual’s _____. All other chromosomes are called _________________. XX- female XY-male X is much ________ than Y. Only small parts of X and Y are ________________. Most genes on the X do not have _________________ on the Y and vice versa. SEX AUTOSOMES LARGER HOMOLOGOUS COUNTERPARTS

Why do we have homologous pairs of chromosomes?
We inherit one from each ____________. Total: 23 (mom) + 23 (dad) n- the number of chromosomes in a __________ set. _________ cell- any cell with two chromosome sets and also a diploid number of chromosomes (2n) Example: Humans- Diploid number is 46 and _____ = 46 Haploid cell- any cell with a _________ chromosome set and also a haploid number of chromosomes (n) Example: Humans- Haploid number is 23 and n = 23 The 23 consist of 22 _________________ and a single sex chromosome. Unfertilized egg cell (________) contains an X chromosome while sperm cell can contain _________________ chromosome. Figure 13.4 PARENT SINGLE DIPLOID 2n SINGLE AUTOSOMES OVUM X OR Y

Human Life Cycle Starts when a haploid sperm cell from the father _______ with the haploid ovum cell from the mother. The fusing of the gametes ends in fertilization, the fusion of their __________. The fertilized egg, _______________, is diploid because of the fusion of the two ______________ sets. As the zygote develops into a mature adult, ____________ generates all the somatic cells by passing both chromosome sets and all the genes. FUSES NUCLEI ZYGOTE HAPLOID MITOSIS

Why not divide by mitosis
The only human cells not produced by mitosis are the __________ which generate in the gonads (ovaries in females and testes in males). Why not divide by mitosis ____________________________________________ Gametes use ____________: a type of cell division which _________________ the number of sets of chromosomes from two to ______ in gametes to prepare for the doubling during fertilization. (_____________ division from diploid to haploid) GAMETES MITOSIS PRODUCES IDENTICAL CELLS MEIOSIS HALVES ONE REDUCTION

Meiosis summary Meiosis overview
Before division, chromosomes are _________________ (_________________). After chromosome replication, there are two _________________ cell divisions: Meiosis I and Meiosis II. Results in ___________ daughter cells instead of two like mitosis. Each daughter cell has ___________ as many chromosomes. Review: Sister chromatids- two copies of one chromosome attached at the centromere and make up one duplicated _________________ Homologous pairs are individual chromosomes that were inherited from _________________ parents and are not _________________. They are similar (same gene location) but not identical. REPLICATED COPIED CONSECUTIVE FOUR HALF CHROMOSOME DIFFERENT CONNECTED

Steps of Meiosis Interphase Chromosomes replicated during the S phase but remain _________________. Each replicated chromosome consists of two identical sister _________________ connected at the centromere. _________________ replicates, resulting in two. UNCONDENSED CHROMATIDS CENTROSOME

Meiosis I Prophase I (usually occupies >_____% of time in meiosis) Chromosomes begin to _________________. Homologous chromosomes pair along lengths and are lined so genes are _________________. ___________________occurs: DNA molecules in non-sister chromatids break at corresponding places and ____________ each other (switch locations). ______________ occurs where a synaptonemal complex forms between homologous chromosomes which holds the chromosomes together tightly. The synaptonemal complex breaks down in late prophase and each chromosome pair becomes visible as a ______________ (a group of four chromosomes) 90 CONDENSE ALIGNED CROSSING OVER REPLACE SYNAPSIS TETRAD

(Prophase I continued)
Each tetrad has at least one _________________ (plural: chiasmata)- a criss-crossed region where crossing over occurred. The chiasmata hold the homologous chromosomes _________________ until anaphase I. Just like in mitosis, _______________ move apart, spindle microtubules form, the nuclear envelope breaks down, and the nucleoli disappear. In late prophase I, the kinetochores of each homologous chromosome attach to _________________ from the poles, then they are moved towards the _________________ plate. CHIASMA TOGETHER CENTROSOMES MICROTUBULES METAPHASE

Metaphase I The pairs of homologous chromosomes (__________) are lined up on the metaphase plate with one chromosome of each pair facing each pole. Both chromatids of a _________________ are attached to kinectochore microtubules from one pole; the other homologue to the microtubules from the opposite pole. TETRAD HOMOLOGUE

Anaphase I Chromosomes move toward the poles, guided by _________________ (microtubules lengthen). Sister chromatids remain attached at the _________________ and move toward a pole. Homologous chromosomes (each contain sister chromatids) move towards _________________ poles. SPINDLE CENTROMERE OPPOSITE

Telophase and Cytokinesis
At the start of telophase I, each half of the cell has a complete ___________ set of chromosomes (each has 2 sister chromatids). Cytokinesis occurs at the __________ time as telophase I and forms two haploid daughter cells. Sometimes chromosomes _________________ and nuclear envelope and nucleoli reform. HAPLOID SAME DECONDENSE

Meiosis II Prophase II _________________ forms. During late prophase chromosomes still have two chromatids move toward the metaphase II plate. SPINDLE

Metaphase II Chromosomes line up on the _________________ plate. The two sister chromatids are not _________________. Kinetochores of sister chromatids are attached to microtubules from opposite poles. METAPHASE IDENTICAL

Anaphase II _________________ of each chromosome separate and chromatids come apart. Sister chromatids (of now individual _________________) move toward opposite poles. CENTROMERES CHROMOSOMES

Telophase II and Cytokinesis MEIOSIS OVERVIEW 2
_________________ form, chromosomes _________________ and _________________ occurs. Meiotic division of one parent cell produces _______ daughter cells, each with a haploid set of _________________. Each of the four daughter cells is __________ from the other daughter cells and parent cell. NUCLEI DECONDENSE CYTOKINESIS FOUR CHROMOSOMES UNIQUE

Mitosis Meiosis Conserves number of chromosome sets Reduces number of chromosome sets from two to one (diploid to haploid) Produces daughter cells genetically identical to parent cell and each other. Produces cells that genetically differ from parent cell and each other. Synapsis and crossing over occur. Tetrad is visible and chiasma forms (due to crossing over) Tetrads on the metaphase plane rather than individual replicated chromosomes. Separation of homologues in anaphase I of meiosis. Sister chromatids stay attached unlike in mitosis where they separate.

2n 2^23 ~ 8 million Genetic Variation: Three Mechanisms
__________________ Assortment independent assortment Independent assortment: the sorting of maternal and paternal _______________ into daughter cells independently of every other pair (occurs during __________________ I). This results from the ___________ orientation of homologous chromosomes during metaphase I. Each chromosome (paternal or maternal) may line up with its maternal or paternal homologue (______% chance for each). Each daughter cell represents _____ outcome of all possible combinations of maternal & paternal chromosomes. The number of possible combinations when chromosomes sort independently is ______. How many possible combinations for humans? INDEPENDENT HOMOLOGUES METAPHASE RANDOM 50 ONE 2n 2^23 ~ 8 million

Crossing over The example above suggests that each chromosome in a gamete is __________________ paternal or maternal, but that is not accurate because of crossing over. Crossing over produces __________________chromosomes, individual chromosomes that carry genes (DNA) from two different parents. Beginning in prophase I, homologous chromosomes pair along the lengths. Crossing over- one maternal and one paternal _______________ of a homologous pair are broken at the same place and rejoined to each other’s DNA. They ____________ places or cross over. In metaphase II, chromosomes contain at least one recombinant chromatid that will go through independent assortment (no longer ______________). crossing over animation COMPLETELY RECOMBINANT CHROMATID TRADE IDENTICAL

Random Fertilization Due to independent assortment during meiosis, a sperm or egg represents one of 8 __________________possible chromosome combinations. The fusion of egg and sperm produces a zygote with one of ~ 64 __________________combinations. This does not account for crossing over… which make the combinations even greater. MILLION TRILLION

Evolutionary Significance?
Natural selection

Ch 12 The Cell Cycle & Mitosis

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