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CLEMSON / Genetics / GEN 3000 / Who came up with the cell theory?

Who came up with the cell theory?

Who came up with the cell theory?


School: Clemson University
Department: Genetics
Course: Fundamental Genetics
Professor: Kate tsai
Term: Fall 2015
Tags: Genetics
Cost: 25
Name: Gen 3000 Week 1 Notes
Description: These notes will be on our first exam on 1/27/2016!
Uploaded: 01/17/2016
6 Pages 39 Views 5 Unlocks

Chapter 1: Intro to Genetics  

Who came up with the cell theory?

People Terms Key Points Questions/Answers

∙ Genetics: experimental science of heredity and the variation of inherited characteristics. I  ∙ First signs of Genetics  

o Domestication of animals  

o Hindu writings said to avoid choosing spouses with undesirable traits to make  sure your children would not have the same traits.

∙ Early ideas on human reproduction and heredity  

o Pangenesis: gemmules carry information from the body to the reproductive  organs. The gemmules would tell the reproductive system that the offspring needs  to have certain traits. This led to support the inheritance of acquired  

How did charles darwin come up with the theory of evolution?


o Inheritance of acquired characteristics: Greek believed that skills would pass  off to offspring through gemmules.  

∙ Robert Hooke: discovered the cell using a microscope.  

∙ Newer ideas on human reproduction and heredity based on discovery of cell o Preformationism: inside the egg or sperm is a miniature adult version called  homunculus. Once fertilized, the homunculus will grow into a bigger version.  o Blending inheritance: blending of the traits of both parents. Neither parent is  giving all of the information to the offspring, it is a blend.  If you want to learn more check out When did the field of medical ethics start?

∙ Schwann and Schleiden: came up with the cell theory.

What is the correlation between genome size and organism complexity?

o Cell Theory: cell divides to offer up more cells. Cells always come from other  cells and are not created on their own.  

∙ Charles Darwin: came up with the theory of evolution through natural selection.  Believed that heredity was the fundamental of evolution.  

o Believed that heredity information is passed down to offspring. This allows for  evolution to occur through natural selection. Undesirable traits will be passed  down and those individuals will be killed off due to natural selection and other  with desirable traits passed on will continue on in life.  

o Darwin’s theory was at a population level. People did not understand his idea due  to not being able to understand genetics at a molecular or family level. He left the  basic ideas unexplained.  

∙ Gregor Mendel: Father of genetics. Chromosomes are still unknown during his time. He  discovered the basic principles of genetics. He used pea plants and analyzed the trends of  the offspring. He was not recognized for his work at the time, people did not understand  it or ignored it.  If you want to learn more check out How important is experience in approach to psychology?

∙ Walter Flemming: observed chromosomes dividing.  

o This discovery allowed for chromosomes to be researched more.  

o It was discovered that chromosomes contain hereditary information and are found  in the nucleus.  

∙ August Weismann: disproved inheritance of acquired characteristics. Proposed new  theory  

o Experiment: cut the tails of rats for multiple generations. If the inheritance of  acquired characteristics theory was true, then the offspring would inherit not  having a tail, since the parents lose it.  

People Terms Key Points Questions/Answers

o Proposed Germ-plasma theory: reproductive system cells contain complete set  of genetic information. The cells are already programed and are responsible for  what offspring characteristics are formed.  

▪ Closest to what we have now

o Modern Genetics: modern genetics mostly occurred during the 90s  

Chapter 2: Mitosis and Meiosis  Don't forget about the age old question of How do countries affect each other in the global economy?

∙ Three major groups of life: Eubacteria (true bacteria), Archaea, and Eukaryotes  ∙ Prokaryotes consist of: Eubacteria and Archaea  

Prokaryotic Cells Eukaryotic Cells 

Nucleus No Yes 

Cell Diameter Small in size Large in size 

Genome Usually one circular DNA Multiple linear DNA 

DNA Not complex Complex and has histones 

Membrane Bounded  Organelles 

None present in cell Some present in cell 

Cytoskeleton Does not contain it Contains it 

∙ No correlation between genome size and organism complexity

∙ The development of the microscope: allowed for differentiation between cells and to be  able to see what is within a cell, such as the membrane bounded organelles  ∙ Bacterial DNA: takes up most of a cell, can be found throughout the bacterial cell  ∙ Eukaryote Chromosome (DNA with proteins): compacted DNA in the nucleus of the  cell. Chromosome is the most compact DNA during cellular division  Don't forget about the age old question of What are the sources of microorganisms in food?

∙ Chromosomes + proteins = Chromatin

∙ Viruses are not cells: pass genetic information and creates new viruses with the help of a  host cell. Cannot reproduce independently  

∙ Prokaryotic cellular reproduction: binary fission  

o Binary Fission: chromosomes replicate -> plasma membranes split -> two  identical cells form

∙ Eukaryotic cellular reproduction: two sets of chromosomes/cell through sexual  reproduction  We also discuss several other topics like How are hormones produced?

o Diploid: 2n, two sets of genetic information  

▪ In most eukaryotic cells

o Haploid: n, one set of genetic information  

▪ Found in gametes (sex cells)

o Humans have 23 pairs

o Homologous pairs: pairs of chromosomes that are alike in structure. Can have  some differences (such as alleles), but are the same in the broad sense.  ▪ Allele: gene for a specific trait such as hair color or eye color  If you want to learn more check out What does anthropology focus on?

∙ Chromosome Structure

People Terms Key Points Questions/Answers

o Telomere: cap on the ends of chromosomes for protection. Example: there is a  cap on the end of shoelace to keep the shoelace from unraveling, it is the same  concept.  

o Centromere: lose chromosomes without it. The connection spot for kinetochore.  Also is used for identification  

o Kinetochore: instrumental for movement, the chromosomes will not be able to  move without it  

∙ Centromere identification

o Arms of chromosomes are distinguished by where the centromere is o P arm: the shorter arm of the chromosome  

o Q arm: the longer arm of the chromosome  

o Metacentric: the arms are almost equal in size  

o Submetacentric: the p arm is slightly smaller than the q arm  

o Acrocentric: the p arm is significantly shorter the q arm  

o Telocentric: the p arm is almost nonexistent  

∙ The Cell Cycle: the cycle that a cell undergoes when dividing.  

o Interphase: Where the growth of the cell occurs. G1-G2. Cannot see the  chromosomes in this stage.  

o G1 Phase: growth of cell. First stage of cell cycle, starting point  

o G0 Phase: halted stage, cell cannot divide. Can reenter G1 phase or stay for an  extended period of time in this phase  

o G1/S Checkpoint: cell must pass this checkpoint before continuing to the next  phase. Once beyond this phase, the cell is committed to dividing.  

o S Phase: Where DNA synthesis occurs  

o G1 Phase: Growth point of the cell, creates enough cytoplasm for division, makes  sure DNA is fully replicated  

o G2/M Checkpoint: Complete checklist of the cell. Is there enough cytoplasm? Is  :  

o M Phase: Nuclear and cell division, Mitosis takes place  

o Cytokinesis: Actual division of the cell into two complete cells. Can reenter the  cell cycle after this stage. This occurs at the same time as the last stage of mitosis  (telophase)  

o Cancer: can be caused if the cell cycle is not maintained. If cells divide that are  not supposed to, it increases the risk of cancer/spread of cancerous cells.  o Cells spend most time in the interphase stage

∙ Mitosis: Prophase -> metaphase -> anaphase -> telophase  

o Mnemonic Device: Please Meet Anna Today  

o Prophase: Chromosomes condense  

▪ Long squiggly lines become short stiff looking lines in homologous pairs.  Are able to distinguish the chromosomes from each other. You have one  of the homologous pair from mom, and the other of the homologous pair is  from dad.  

▪ Centrosomes move to the sides of the cell and the mitotic spindle forms  from the centrosomes. This occurs only in animals, not plants  

▪ Nuclear envelop starts to disappear  

o Prometaphase: Nuclear envelope disappears completely  

People Terms Key Points Questions/Answers

▪ The microtubules stretch out and reach the chromatids. They connect to  the kinetochore  

o Metaphase: Chromosomes arrange in a straight line.  

▪ The chromosomes arrange independently in the middle of the cell in a  straight line (side by side), this line is called the metaphase plate

o Anaphase: Sister chromatids move to opposite poles  

▪ Spindle fiber pulls on the kinetochore causing the sister chromatids to split  and move in opposite directions. This is called disjunction

o Telophase: Chromosomes arrive at the poles and the nuclear membrane reforms.  ▪ Two nuclei are in one cell during this phase. This is a short period of time  and happens before cytokinesis occurs.  

▪ Can no longer see the chromosomes  

▪ If done correctly, two cells are an exact copy  

▪ Cytokinesis occurs at the same time of this phase. Once the nuclear  membrane reforms, the cytoplasm starts to split and creates two separate  cells. This occurs by pinching in the sides.  

∙ How do Chromosomes move?

o Spindle fibers are a moving mechanism that attaches to the chromosomes at  the kinetochore.

o Spindle fiber is made up of individual units called tubulin subunits. Tubulin  subunits can be added to expand the length of the spindle fiber causing the fiber to  move forward (away from centrosomes) or can be taken away to shorten the  length of the spindle fiber causing the fiber to move backwards (towards  centrosomes). This is how the spindle fibers are able to move chromosomes  ∙ Where does the force to move chromosomes come from?

o Depolymerization of tubulin at the positive end. This causes the microtubules  to shorten  

o Molecular Motors: Tells the microtubules to either add or take away tubulin  subunits to lengthen/shorten the fiber as needed  

∙ Why do some drugs specifically target spindle fibers?

o If the movement of chromosomes is prevented, then the cell cannot divide. This  causes the cell to freeze or possible even die. This can stop bad (cancerous) cells  to divide and stops the spread of the disease.  

∙ What could happen if the spindle fiber breaks and the process of splitting the sister  chromosomes stops?

o If the cell continues to divide, there can be a loss or an excess of chromosomes.  For example: if there is a loss of a sex chromosome due to the breaking of the  spindle fiber, it can develop into turner syndrome  

∙ What regulates the cell cycle?

o The cell cycle is regulated by proteins. Cells have a specific protein pattern that  helps the cell to know what stage needs to take place of the cell cycle.  

o MPF = cyclin B + CDK  

▪ Cyclin B and CDK work together to form MPF. All of these impact the  cell cycle and the stages that take place.  

People Terms Key Points Questions/Answers

▪ For example: Cyclin B drops builds up slowly during interphase and then  drops off during mitosis, this continues. If it did not drop off, it may push  the cell to divide when the cell is not ready.  

Mitosis Meiosis 

Number of Nuclear  


Number of Chromosomes in  the End 

Single nuclear division takes  place 

The two cells created have  the same number of  

chromosomes as the parent  cell

Two nuclear divisions takes  place 

The four cells created have ½  of the number of  

chromosomes as the parent  cell

Types of Cells Created Two genetically identical  cells 

Four genetically variable cells  (will be discussed later) 

∙ Meiosis: gives unique cells that are haploid. Are in the gametes  

o Middle Prophase I: chromosomes begin to condense. And spindle fibers form.  Much like Mitosis prophase  

o Late Prophase I: homologous chromosomes pair together this action is called  synapsis. 1 of the homologous chromosomes will be from mom and the other is  from dad. Crossing over of the homologous pairs occurs. Nuclear membrane  breaks down  

▪ Crossing Over: chromosomes get stuck together and form a chiasma (the  allele that the crossing over takes place at). It is a type of intertwining  

between two nonsister chromatids  

∙ Allows for genetically different cells

∙ Example: Chromosome 1 from dad will intertwine with  

chromosome 2 from mom. A physical break down of the  

chromosomes takes place at a certain point and the pieces rejoin  

with the other chromosome. This causes chromosome 1 from dad  

to have part of chromosome 2 from mom. Makes all cells unique.

∙ What would happen if crossing over occurred between two  

sister chromatids?

o Nothing genetically would be wrong with the  

chromosomes, but the cells would no longer be genetically  


o Metaphase I: The homologous pairs of the chromosomes move dependently to  each other and align on the metaphase plate. Microtubules connect to the  kinetochore of a pair.  

o Anaphase I: homologous pairs are separated. One copy of each pair is on  opposite poles. (Example: pair from dad is on one pole, pair from mom is on the  other). This is when the cell becomes haploid due to the reduction of  chromosomes!!  

o Telophase I: Chromosomes reach the spindle poles and condense, the nuclear  membrane finishes reforming, and the cytoplasm divides the cell into two. o Prophase II: chromosomes re-condense and the nuclear membrane begins to be  broken down.

o Metaphase II: Chromosomes align on the metaphase plate but they move  independently, microtubules attach to the kinetochores (this is like metaphase I,  

People Terms Key Points Questions/Answers

the only difference is the chromosomes moving dependently vs. independently of  each other).,  

o Anaphase II: sister chromosomes are pulled apart from each other and are now  chromosomes

o Telophase II: chromosomes arrive at the poles, nuclear membrane reforms, and  the cytoplasm divides making the two cells into four

o Products of Meiosis: all four cells are haploid, each have one copy of chromatid,  each genetically unique cells

∙ Cells are genetically distinct from Meiosis because…

o Crossing over of nonsister chromatids  

o Random distribution of chromosomes during anaphase I (When pulled apart,  there is not a set pole for one to go, can line up in different orders).

∙ How is meiosis different in males and females?  

o In males: Once starts it is a continuous process, standard meiosis

o In females: long drawn out process, only completes if fertilization takes place, not standard meiosis.

▪ During meiosis I, the cytokinesis phase does not divide cytoplasm  equally. This produces a polar body (polar body is too small and will not  continue in meiosis process).  

▪ The secondary oocyte continues on with meiosis II.  

▪ During meiosis II, the cytokinesis phase does not divide cytoplasm  equally. This produces another polar body (polar body again is too small  and will not become an ovum and will not be fertilized.

▪ Females do not get four in the end, only get one.

▪ Why create polar bodies with not enough cytoplasm?  

∙ The egg needs as much nutrition as possible so it will get the extra  cytoplasm for fertilization.

∙ Plant cycle: plants go between diploid (sporophyte) and haploid (gametophyte). o From meiosis two megaspores are created that are haploid, one is male and the  other is female. They then fertilize and create a zygote that becomes a sporophyte  and this is diploid. It then goes back to meiosis.

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