A- Cell Reproduction Notes.pdf
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Cellular Reproduction Chapter 16 Check this out!: https://www.ncbi.nlm. nih.gov/books/NBK22 266/ Cellular Reproduction There are 2 main types of cells in the human body that we will discuss throughout Biology 30. 1. Somatic cells: body cells; each has 2 sets of similar chromosomes...
Cellular Reproduction Chapter 16 Check this out!: https://www.ncbi.nlm. nih.gov/books/NBK22 266/ Cellular Reproduction There are 2 main types of cells in the human body that we will discuss throughout Biology 30. 1. Somatic cells: body cells; each has 2 sets of similar chromosomes diploid = 2n 2. Germ cells: any line of cells that give rise to gametes (eggs in females and sperm in males), have a single set of chromosomes haploid =n Asexual Cell Reproduction Called asexual because no new combination of genetic material occurs – all new cells produced contain the same genetic material as the original cell. occurs in many organisms, as well as our somatic cells: Growth Repair Replace old cells Sexual Cell Reproduction introduces genetic variation results in the combination of genetic information from two parental cells requires a reduction in the chromosome number for each gamete n + n = 2n Occurs in our germ cells Watch Amoeba Sisters: https://www.youtube.com/watch?v=fcGDUcGjcyk Sexual Cell Reproduction Called “sexual” because a combination of cellular material occurs – new cells produced contain genetic material from two combining cells. What is the advantage to this? What would happen to the total number of chromosomes in the egg and sperm had the same number of chromosomes as all your body cells? Haploid – Diploid Life Cycle Gametes (egg and sperm) have 23 single chromosomes haploid number (n) When the ova is fertilized by the sperm, the original number of chromosomes (46 = 2n) is restored by forming a zygote All plants and animals have a characteristic number of Organism Diploid number (2n) chromosomes in their Cat 38 somatic (body) cells Dog 78 called the diploid Horse 64 Donkey 62 number (2n). Yeast 32 In humans the diploid Wheat 42 number is 23 pairs Ant (sp. Myrmecia pilosula) 1 (2x23) for a total of 46 Fern (sp. 1260 chromosomes. Ophioglossum reticulatum) 2n = 46 The chromosomes in humans are numbered from 1-22. These are called autosomes and exist in pairs (one from your mom and one from your dad). Both autosomes contain genes for the same types of characteristics and are the same size and shape Known as homologous chromosomes The last “pair” of chromosomes (#23) determines biological sex at birth (sex chromosomes) If it is a homologous pair (2x chromosomes) then the individual is female at birth. If the pair is made of one rod shaped and one hook shaped chromosome (an x and a y) then the individual is male at birth. The “x” and “y” chromosomes carry information for many different characteristics, not just those related to biological sex. The Cell Cycle The cell cycle does not start and stop, but continues – different cells may go through the cycle at a different pace. Parent cell Daughter Cell Interphase – Resting Phase Up to 90%(!!) of the cell cycle. Divided into three separate phases: 1. G1 phase: (Gap 1 or Growth 1) – general growth & organelle replication Interphase 2. S phase (synthesis): Replication of genetic material (DNA) need 2 copies of each strand of DNA, one for each new cell (called sister chromatids) DNA exists as chromatin during interphase because uncoiled DNA is easier to transcribe in order to synthesize proteins Interphase – Resting Phase 3. G2 phase (Gap 2 or growth 2): structures associated with cell division are replicated as well as rebuild energy stores Genetic Material Watch out for the “c’s”! DNA is found in a different form depending on the stage of the cell cycle: Chromatin – long, thin threadlike material - present in this state during interphase Chromosomes – small, condensed, may be found as individual chromatids or as linked identical sister chromatids connected at the centromere after replication. Cell Death and the Aging Process Cells in the body divide at different rates, and have different life spans Number of times a cell can divide appears to as specialization Some very specialized cells (mature muscle, red blood cells, nerve cells) no longer divide and remain in G1 forever Cells appear to have a finite # of cell divisions built in – maximum life span remains at ~115 yrs WHY can’t cells continue reproducing forever? Cancer Defined as the rapid, uncontrolled division of cells Cancer cells have lost the ability to differentiate and carry out cell processes Cancer cells spend most of their time in mitosis, rather than in interphase doing their jobs Cancer TEDEd - How do cancer cells behave differently from healthy ones? A tumor is a mass of undifferentiated cells which interferes with the normal functioning of the surrounding tissues. Tumors are believed to be the result of one transformed cell Metastasis - the spreading of cancer cells through the body, create tumors in new location Cancer Prevention focuses on the elimination of carcinogenic/teratogenic/mutagenic substances that damage DNA and are thought to damage the cell’s ability to control cell division (diet, tobacco, UV rays) Treatments are focused on processes that can stop or slow down mitosis, gene therapy that “turn on” the immune system to attack cancerous cells and surgery to remove the cancer Cell Division – Somatic Cells Two main processes: 1. Mitosis – division of the genetic material into two nuclei. (follows interphase) 2. Cytokinesis – division of the cytoplasm and organelles into two separate cells Mitosis and Cytokinesis - LearnAlberta Mitosis Allof the cells produced by mitosis are IDENTICAL in genetic makeup to the original cell the chromosome # doesn’t change (diploid cells) DNA exists as chromosomes – coiled & condensed, chromosomes are more easily moved around and separated equally Amoeba Sisters Mitosis Video: https://www.youtube.com/watch?v=f-ldPgEfAHI Mitosis – Prophase nuclear membrane disappears DNA strands shorten & thicken; chromatin chromosomes Each chromosome has 2 sister chromatids that are joined by a centromere centrioles separate & move to opposite poles of the cell, spindle fibers start to appear Mitosis – Prophase Prophase Mitosis – Metaphase Spindle fibers attach to the centromeres and guide the chromosomes to line up at the equator (center of the cell) One sister chromatid faces each pole Mitosis – Anaphase Sister chromatids separate at the centromeres and move to opposite poles of the cell, pulled by spindle fibres the same number of single-copy chromosomes should be at each pole Mitosis – Telophase chromosomes at opposite ends of the cell Uncondense to form chromatin Nuclear envelope reappears around each set of chromosomes Spindle fibres disappear Cytokinesis Division of cytoplasm and organelles into two cells in plant cells, a cell-plate forms first between the two masses of chromatin, the cell plate will eventually form the cell wall in animal cells, the cell membrane pinches in along the cell equator and continues to deepen until the cell is pinched in two (called cleavage) Cytokinesis Cytokinesis Can you identify cells in the various stages of mitosis on this root tip image? Quantity of DNA in a Cell During the Cell Cycle 2x46 DNA Cytokinesis Content DNA Synthesis 46 G1 S G2 P M A T G1 Cycle Phase Meiosis Meiosis– special form of cell division occurring only in the reproductive tissue (germ cells) of sexually reproducing organisms where haploid (n) gametes are formed, having half the DNA content of the original sex-forming cell. Involves two cell divisions (instead of the one in mitosis) leading to four haploid cells formed (instead of two diploid in mitosis) Stages of Meiosis Meiosis I (“Reduction Division”) - the chromosome # is reduced from 2n n Interphase G1,S, and G2. Replication of chromosomes. Prophase I Contents of the nucleus become visible (DNA strands shorten & thicken; chromatin chromosomes) Nuclear membrane disappears Centrioles separate & move to opposite poles of the cell, spindle fibres start to appear Prophase I Homologous chromosomes pair up side by side (synapsis) so that the same genes are next to each other forming a tetrad The homologous chromosomes will criss-cross over each other (forming a chiasma), and occasionally break and exchange segments (called crossing over) identical segment sizes are exchanged Metaphase I Homologous chromosomes move to the center of the cell, centromeres on the equator, side by side. The order that chromosomes line up with their homologous pair increases the diversity of genetic variation in the gametes (independent assortment) Anaphase I Homologous pairs separate not sister chromatids separating at the centromere!!! Chromosomes move to opposite poles of the cell called: segregation There should be 23 doubled chromosomes at each pole (each chromosome remains double stranded) Telophase I Chromosomes at opposite ends of the cell Chromosomes don’t uncondense to form chromatin Nuclear envelope occasionally reappears (in some cells) Cytokinesis occurs 2 cells, each has 23 chromosomes REDUCTION DIVISION! Meiosis II Essentially the same as mitosis except cell is now haploid Prophase II centrioles separate & move to opposite poles of the cell, spindle fibers start to appear Metaphase II Chromosomes align at the center of the cell, centromeres on the equator Spindle fibres attach to the centromeres Anaphase II Sisterchromatids separate at the centromeres Chromatids move to opposite poles of the cell There should be 23 single chromosomes (ie. 23 chromatids) at each pole Telophase II Chromosomes at opposite ends of the cell Uncondense to form chromatin Nuclear envelope reappears Followed by Cytokinesis (cleavage) Amoeba Sisters Meiosis : https://www.youtube.com/watch?v=VzDMG7ke69g Meiosis vs Mitosis Draw! Practice practice practice (lots of questions + answer keys to try on D2l – I suggest you print the practice) Videos (Khan academy, amoeba sisters (https://www.youtube.com/watch?v=zrK dz93WlVk ), crash course). SO, where does the variation come from? 1. Crossing over during Prophase I 2. Independent assortment (meiosis 1): for organisms with just 3 chromosome pairs (2n=6), there are 8 possible assortments of chromosomes (23) In humans, with 23 pairs of chromosomes, 8 388 608 different gametes could be formed due to the random/independent assortment of genes during meiosis 1. http://www.learnalberta.ca/content/seb30/html/interactiveL auncher.html?interactive=ComparisonMeiosisMitosis.swf Gametogenesis – p. 569 The formation of ova and sperm from meiosis Cells that have gone through meiosis do not ever divide again…they have a job to do (specialized) Spermatogenesis Spermatogenesis is the production of mature sperm and occurs from puberty through life in males Sperm are designed for movement (little cytoplasm or organelles), lots of cell division, 4 small sperm produced http://www.learnalberta.ca/content/seb30/html /interactiveLauncher.html?interactive=Spermato genesis.swf Oogenesis Oogenesis is the development of ova (mature, unfertilized egg cells) Eggs are designed to nourish the zygote – only one ovum is produced per oocyte the other 3 polar bodies sacrifice their cytoplasm to produce one large egg In females, meiosis begins before birth and is suspended in prophase I from birth until puberty Starting at puberty, a single primary oocyte usually completes meiosis I each month The second meiotic division only completes if fertilization occurs Compare and contrast Spermatogenesis Oogenesis 1. diploid germ cells in a 1. Oogonium is the starting male’s testicles called diploid germ cell spermatogonia 2. Hundreds of millions of 2. Each oogonium divides by mitosis to form two sperm produced regularly, primary oocytes (this occurs constantly happening in female fetus) 3. At puberty the spermatogonia divide by 3 months old fetus has over mitosis. One of the 2 million primary oocytes daughter cells replenish the spermatogonia 4. Primary oocyte starts population, the other meiosis but are frozen in develops into a primary prophase I until puberty spermatocyte Typical Genetic Sex Determination The sex of a zygote is determined by the sex chromosomes (the X & Y chromosomes) The Y-chromosome contains a gene known as TDF (Testes Determining Factor) Any zygote with a Y chromosome is therefore male (XY) A zygote with two X chromosomes is female To see a TedEx about atypical sex chromosome and other reproductive anomalies, see the following link: https://go.ted.com/CAq7 Molly Webster: The weird history of the "sex chromosomes" https://go.ted.com/6F7T Random fact Mulesare sterile because they cannot form gametes- there are no homologous pairs to synapse during prophase I (horse 2n=64, donkey 2n=62, mule 2n=63) Problems During Cell Division (Meiosis I or Meiosis II) Nondisjunction – when chromosomes don’t separate during anaphase – one of the daughter cells produced during that separation will be lacking information, the other one will have too much. “Chromosomal mutations”. After fertilization: if there is one too many chromosomes, one pair will be a triplet trisomy if there is one too few chromosomes, one pair will be a singlet monosomy Nondisjunction and Fruit Seedlessfruits are made by manipulating chromosome number so that meiosis is impossible (usually creating a triploid number) Ploidy Some plants have a large ploidy number and cross breeding these can results in sterile offspring: Ex: Watermelon A = 8n Watermelon B = 6n If these watermelon go through meiosis (recall: reduction division – reducing their regular ploidy by half), 1. What will be the ploidy of their offspring? 2. Will it be fertile (be able to produce its own offspring)? answer 8n / 2 = 4n (sex cell) 6 n /2 = 3 n (sex cell) Combine the sex cells 4n+3n = 7n - therefore sterile (can’t do meiosis properly because odd number of chromosomes). Karyotyping To evaluate the chromosomal composition of cells in an embryo, fetus or full-grown organism, a karyotype is made – rapidly dividing cells are isolated and stained, then the chromosomes from cells in metaphase are analyzed Chromosomes are cut out and matched according to the banding patterns Karyotyping Atypical karyotyping will show the result of non-disjunction during meiosis or mitosis (important in cancer research and diagnosis) Karyotyping will also determine typical sex at birth pair #23 (the “sex chromosomes” – if XY male, if XX female Human disorders due to chromosomal issues Most non-disjunctions during gametogenesis will produce sperm/ova resulting in a nonviable fetus that will spontaneously abort (miscarry) during early development If the nondisjunction still allows the fetus to develop to term, a group of disorders may result Biology 30 Image Collection Down’s Syndrome Affects 1 in 700 children born Frequency correlates with the age of the mother (and maybe the father?) Results from an extra chromosome 21 (trisomy 21) Characteristic facial features, short stature, heart defects, susceptibility to respiratory infection, and mental retardation Average lifespan is shorter Sexually underdeveloped and sterile Klinefelter Syndrome An extra X chromosome in a male (XXY) Occurs 1 in every 2000 live births Have male sex organs, but man is sterile Often includes breast enlargement and other feminine characteristics Normal intelligence Turner Syndrome Contain only 1 X chromosome (X0) Occurs 1 in every 5000 births Appear female however sex organs do not mature at adolescence, and secondary sex characteristics fail to develop Sterile, short stature Normal intelligence Cri du chat Other chromosomal abnormalities are a result of an addition or deletion of an arm of a chromosome: Deletion of a part of chromosome 5 Occurs 1 in every 20 000 live births Characteristic cry similar to a meowing cat Feeding problems, low birth weight, severe cognitive, speech and motor delays Diversity of Reproductive Strategies exists… Alternation of Generations https://www.youtube.co m/watch?v=iWaX97p6y9 U Moss life cycle 1. What process happens at the point labelled A? 2. What is the ploidy (diploid or haploid) of the spores in the diagram to the left? 3. What process produces the sperm and egg in the moss life cycle 4. What is the process at B? (spore to multicellular gametophyte) Answers 1. fertilization (meeting of sperm and egg – produces the diploid zygote). 2. spores are haploid – meiosis is reduction division going from 2n n 3. mitosis – because haploid gametophyte undergoes mitosis to make haploid sperm OR egg cells. 4. mitosis – single cell spore (n) does mitosis (nn) to produce a multicellular gametophyte Asexual Reproductive Strategies Many simple organisms (ex. Bacteria, paramecium, yeast), fungi and plants use asexual reproduction rather than sexual reproduction. What advantage does this have? Parthenogenesis https://www.youtube.com/watch?v=1mS 10pRK8rE Science, Tech, and Society Cancer Cloning Twins Stem cells Cloning https://www.youtube.com/watch?v=FjBgLIE7514 https://www.youtube.com/watch?v=tELZEPcgKkE Twins – Natural Clones Identical twins form when a cell breaks free from the undifferentiated embryo and develops on its own Identical twins are clones of each other – they share the same DNA http://publications.nigms.nih.gov Fraternal Twins Fraternaltwins form when two eggs are fertilized and implant at the same time These twins may appear different http://www.inkycircus.com because they do not have identical DNA Stem cells Pluripotent: A cell able to develop into a # of specialized cells, such as a neuron or muscle cell Totipotent A cell able to give rise to all parts of the embryo and adult, as wells as extraembryonic membranes Significant for research Embryonic Stem Cells Can Become Any Tissue in the Body (totipotent) Cultured Laboratory Stem Cells Blastocyst Scientific manipulations entice stem cells to become specialized tissues (blood, muscle, brain etc.). Blood Cells Muscle Cells Neuron (Brain) Cells Potential of stem cell research Cloning organs from adult stem cells – to reduce rejection of donated tissue and wait time for donated organs. Bone marrow transplants of stem cells Used to test medical treatments in the lab Understanding factors for growth and development There are numerous therapeutic potential benefits of stem cell research. Check out this paper if you are interested: https://royalsocietypublishing.org/doi/full/10.1098/r stb.2009.0149#d3e538
