Biology 30: Cell Division Ch. 16 PDF

BIOLOGY 30 Cell Division Unit C: Chapter 16  TOPIC 1: MITOSIS ○ somatic cells vs. sex cells ○ autosomes vs. sex chromosomes ○ chromosomes vs. chromatin ○ homologous chromosomes vs. sister chromatids ○ haploid (n) vs. diploid (2n) ○ stages of interphase: G1, S, G2 ○ stages of mitosis: p...

BIOLOGY 30 Cell Division Unit C: Chapter 16  TOPIC 1: MITOSIS ○ somatic cells vs. sex cells ○ autosomes vs. sex chromosomes ○ chromosomes vs. chromatin ○ homologous chromosomes vs. sister chromatids ○ haploid (n) vs. diploid (2n) ○ stages of interphase: G1, S, G2 ○ stages of mitosis: prophase, metaphase, anaphase, telophase ○ cancer, cloning, and stem cells ○ telomeres & aging Textbook pgs. 556-571  Why do Cells Divide? 1. Replace damaged cells. 2. Growth of organism. 3. Reproduction. From the moment of fertilization, cells are continuously growing, dying, and being replaced… 2 Types of Cell Division ○ 1. Mitosis ○ Somatic cells (body) ○ Two identical daughter cells ○ 2. Meiosis ○ Sex cells (gametes) ○ Sperm and egg ○ ½ number of chromosomes Asexual Reproduction (Mitosis) – a single individual (like a yeast cell CELL CYCLE: MITOSIS or amoeba) is the sole parent and passes copies of all its genes to Question: With little to no genetic differences, how its offspring without the fusion of would a simple disease affect a gametes – process of MITOSIS. population of asexual organisms? The daughter cell’s genes are virtually exact copies of the parent’s genome – gives rise to a clone. NOTE: Genetic difference do occasionally arise in asexual reproduction due to changes in the DNA called mutations. Sexual Reproduction (Meiosis) – two parents give rise to offspring that have unique combinations of genes inherited from the two parents. ○ There are variations in family resemblance, not exact replicas – because of the process of MEIOSIS. ○ During meiosis, there is a shuffling of genes when gametes cells are created – this is called CROSSING-OVER. ○ Due to crossing-over, the population has more genetic diversity – higher chance of survival when environmental conditions change (NATURAL SELECTION).  Chromosomes Histones: proteins that provide structural support for the chromosome ○ Chromosome: Condensed organized structure of DNA. ○ Chromatid: Arm of Chromosome. ○ Centromere: Region in middle of chromosome where sister chromatids attach. ○ Exists in single chromatids. ○ Chromatin: ○ DNA + proteins (histones) ○ Sister Chromatids: Two identical chromatids. ○ Only occurs after Replication. ○ Attached at centromere.  Chromosome duplication Sister Centromere chromatids Chromosome distribution to daughter cells Homologous Chromosome: ○ Pair of chromosomes with the identical features. ○ One from mom, one from dad. Karyotype  Karyotypes Karyotypes: a display of chromosome pairs ordered by size and length Pair of homologous duplicated chromosomes Note: in actual karyotypes it is difficult to see the sister chromatids in each pair Sister Chromatids Karyotypes ○ A picture of an individual’s chromosomes In order Autosomes 1 – 22 and Sex Chromosomes X & Y ○ get this picture, the chromosomes are isolated, stained, and examined under the microscope ○ Most often, this is done using the chromosomes in the white blood cells (easily stainable) ○ Each will vary in length, location of their centromere and staining properties Centromere Sister chromatids Pair of homologous chromosomes 5 A Human Karyotype An Abnormal Mouse Karyotype Chromosomes and Karyotypes Amoeba Sisters https://www.youtube.com/watch?v=mBq1ULWJp_M  Chromosome Number varies from species to species… Bananas = 22 Humans = 46 Dogs = 78 Ferns = 1260 More chromosomes DOES NOT necessarily result in higher intelligence or complexity Human Chromosomes ○ Human cells contain 46 single chromosomes = to 23 pairs ○ 22 pairs of autosomes (any chromosome that is not a sex chromosome ○ 1 pair of sex chromosomes – either XX or XY) o Homologous chromosomes are chromosomes with the same gene sequence as one another; one homologue is of maternal origin, and the other is of paternal origin. o Although homologues carry the same set of genes, they may carry different forms of the each gene (a.k.a alleles) o Because human cells carry two pairs of each chromosome, we are said to be diploid  Human somatic cells are diploid, or “2n” Human gametes (sex cells) are haploid, or “n” 2n = 46 n = 23 Some organisms, such as earthworms, contain more than two homologous chromosomes in each cell. These organisms are said to be polyploid. 3n = 54 n = 18 ○ Cells are the end of mitosis are diploid and have the same number of chromosomes. ○ Human body cells have 46 chromosomes. Complete the following table of chromosome number in various species Species Number of Number of homologous Number of Chromosomes in diploid chromosome pairs in chromosomes in haploid cells (2n) diploid cells cells (n) Fruit Fly 2n = 8 1. 4 pairs 2. n = 4 Leopard Frog 2n = 26 3. 13 pairs 4. n = 13 Housefly 5. 2n = 12 6. 6 pairs n=6 Monkey 7. 2n = 42 8. 21 pairs n = 21 Bat 9. 2n = 44 22 pairs 10. n = 22 Chicken 11. 2n = 78 39 pairs 12. n = 39 King Crab 13. 2n = 208 104 pairs 14. n = 104 Camel 2n = 70 15. 35 pairs 16. n = 35 Goat 17. 2n = 60 18. 60 pairs n = 30 Armadillo 19. 2n = 64 20. 32 pairs n = 32 The Cell Cycle Cell Division: The process by which a cell divides and creates new daughter cells. ○ 1. Mitosis: Division of somatic (body) cells. ○ 2. Meiosis: Division of gametes (sex) cells. Cell Cycle Each new cell, or daughter cell, must contain the same genetic information as the original cell, or parent cell (occurs through DNA replication and cell division) parent cell: DNA is this genetic information. It is found within the nucleus of each and every cell in the body.  Preparing for Cell Division – the chromatin becomes highly compact, and the chromosomes are visible with a light microscope – Early in the division process, chromosomes duplicate – Each chromosome appears as two sister chromatids, containing identical DNA molecules – Sister chromatids are joined at the centromere, a narrow region Copyright © 2009 Pearson Education, Inc. Chromatin: Unpackaged DNA in the nucleus of the cell Mitosis Rap ○ https://www.youtube.com/watch?v=pO sAbTi9tHw  The Cell Cycle Goal: to produce daughter cells with the same DNA as the parent cell Divided into two Phases: 1. Interphase: Normal cellular functions, replication occurs. Growth Stage 2. M-Phase (Mitosis and Cytokinesis) Cell divides DNA and cytoplasm to produce two new daughter cells.  INTERPHASE S G1 (DNA synthesis) sis e G2 in s k si to y ito C M M IT PHA OTIC SE (M) Interphase Each cell goes through three phases before it actually divides: 1. G1 Phase (cell growth) 2. S Phase (DNA replication) 3. G2 Phase (preparation for division) Cell continues to grow. Interphase is followed by cellular division, or “M phase”. ○ Interphase ○ Dark nucleus in middle. ○ Chromosomes have not condensed yet. ○ “Think Dark Center” Division Stage (M-Stage) 2 processes involved: 1. Mitosis – division of the nucleus 2. Cytokinesis – division of the cytoplasm Mitosis (Amoeba Sisters) ○ https://www.youtube.com/watch?v=f-l dPgEfAHI  Mitosis Mitosis is performed by all autosomes. It is a form of cell division that produces daughter cells that are identical to parent cells. The extent of repair varies from organism to organism Mitosis Mitosis & Growth  Mitosis After DNA replication (interphase), cells go through four stages of mitosis before cytokinesis can occur:  1. PROPHASE At this stage, each pair of homologous chromosomes has been duplicated, so the cell contains twice as much DNA than normal: o Chromatin condenses to form chromosomes o Nuclear membrane breaks down o Centrioles move to opposite poles of the cell and spindle fibres begin to form (spindle fibres are required to eventually pull the duplicated chromosomes apart) Early & Late Prophase in a Plant Cell 2. METAPHASE o Spindle fibres attach to the centromere of each chromosome, guiding them to the equator of the cell o Duplicated chromosomes line up in single file, forming the “metaphase plate” Metaphase in a Plant Cell  3. ANAPHASE o Spindle fibres shorten and sister chromatids are pulled apart from one another; centromeres split o Two opposing poles are formed, each with a complete diploid set of DNA Anaphase in a Plant Cell  Quick Review Homologues vs. Sister Chromatids Sister chromatids – two identical chromatids held together by a centromere Homologous pairs (homologues) -in every diploid cell each chromosome has a partner. The two resemble each other in size, shape and type of genetic information contained but not in form of genetic information  Homologous chromosomes are not identical to one another, because they carry different forms, or alleles, of the same genes. - They have several other characteristics in common, such as their length, centromere location, and banding pattern. 4. TELOPHASE o Chromosomes reach opposite poles of the cell o Spindle fibres break down o Chromosomes begin to unwind into chromatin o Nuclear membrane forms around each new set of genetic info. Telophase – Plant & Animal Cells Cytokinesis o Cytoplasm splits to form two identical daughter cells with the same genetic content as the original parent cell o Daughter cells are now in G1 of interphase Cytokinesis –division of the cytoplasm ○ In animal cells ○ Cell membranes begin to pinch together from the o/s inward forming the cleavage furrow ○ In plant cells ○ The cell plate begins to appear midway across the cell forming from the inside outward Cytokinesis in an animal cell. Cleavage Furrow  Telophase and cytokinesis in plant cells looks a bit different… o Because plant cells contain a rigid cell wall, cytoplasm will not furrow and pinch off o Instead, a cell plate forms between the two daughter nuclei, eventually developing into a cell wall  Wall of Cell plate Daughter parent cell forming nucleus Cell wall New cell wall Vesicles containing Cell plate Daughter cells cell wall material  Mitosis & Cell Division in Plants ○ Basically mitosis and cell division in plant cells is similar to that in animal cells. The two main differences are: 1. Plant cells do not have centrioles (still form a spindle) 2. Plants form a cell plate rather than a cleavage furrow. By the end of telophase cellulose & protein have been added to form a new cell wall. Mitosis in Plant Cells:  If you were to look at a sample of healthy tissues under a microscope, most of the cells you would observe would likely be in interphase/early prophase… Why??? ○ 95% of cell cycle in Interphase. ○ 5% of cell cycle in Mitotic Phase. Can you identify stages of MITOSIS in the image below? Check Points (cell control System) ○ Proteins in cell regulate how much a cell goes through mitosis. ○ Checkpoints within cell cycle ○ If the Cell does not pass a check point, the cell will not divide. What would happen if cells were constantly dividing? No Control CANCER Cancer & the Cell Cycle Uncontrolled cell division may be caused by exposure to mutagens, or agents which change an organism’s genetic material. Mutagens may be physical, chemical, or biological in origin. Mutagens that specifically lead to the formation of cancerous cells are further classified as carcinogens. Carcinogens: Cancer-causing substances that can lead to a mutation in DNA. Examples Radiation UV from the sun and tanning lamps X-rays: medical and dental Smoking/Chewing Unhealthy chemicals in cigarettes. Unhealthy Drinking/Eat Alcoholic beverages, processed foods, etc. Environmental Car exhaust, fumes, work chemicals  The uncontrollable Cancer Cells growth of cancer cells can lead to a tumor (a mass of tissue formed by abnormal cells) Benign tumor: cells are abnormal, but not considered to be cancerous (yet) Cells remain at only the tumor site and are unable to spread elsewhere in the body Malignant tumor: mass of cancerous cells that lose their anchorage dependency and can leave the tumor site Metastasis: when cells separate from the tumor and spread elsewhere in the body Treatment ○ Chemotherapy: treatment that uses powerful chemicals to kill fast-growing cells in your body ○ Surgery: Removal of Tumor ○ Radiation Therapy: Use of radiation to kill cancer cells. ○ Immunotherapy: Training of your immune system to fight cancer. Applications of the Cell Cycle: Cloning Cloning is the process of forming identical offspring from a single cell or tissue of a parent organ. Cloning is a form of asexual reproduction. Many species utilize this form of reproduction (e.g. plants, bacteria, hydra) A form of cloning also results in the production of twins; if a single fertilized egg accidentally undergoes mitosis and splits in two, identical or monozygotic twins occur, each with the exact same DNA. Non-identical or dizygotic twins form when two eggs are ovulated at once, and are fertilized by different sperm. Dizygotic twins do not share the same genetic information. Animal Cloning Technology Organisms can be artificially cloned as well…  Stem Cell Research Most cloning-based research has focused on cloning individual cells, tissues and organs from stem cells (cells that have not yet become specialized)… What might be some useful applications of this research???  Stem Cell Ethics Only a zygote is truly totipotent; it is considered unethical to obtain stem cells from this source. Pluripotent stem cells, however, can easily be obtained from adult tissues. https://www.genome.gov/25020028/cloning-fact-sheet/  Mitosis and Aging Telomeres are caps found at the end of each chromosome. Every time a cell divides, its telomeres shorten. Eventually, the telomeres become so short that a cell will no longer be able to undergo mitosis, and cell death occurs. Telomere length thus serves as a sort of “molecular clock” for cellular aging. https://www.cnet.com/news/nasa-twins-study-scott-ma rk-kelly-space-station-telomeres/  Telomeres that do not shorten with each cell division may be indicative of cancerous cells… http://med.stanford.edu/news/all-news/2018/04/telomerase-expressing-liver-cells-regenerate-the-organ.html  Long-Term Consequences? https://www.newscientist.com/article/dn3393-dolly-the-sheep-dies-young/ Mitosis overview: Questions Human cells have 46 chromosomes. By the end of interphase – How many chromosomes are present in one cell? – 46 – How many chromatids are present in one cell? – 92 (each chromosome has been duplicated and consists of a pair of chromatids joined at the centromere) By the end of metaphase How many chromosomes are present in one human cell? ○ 46 How many chromatids are present in one human cell? ○ 92 By the end of anaphase – How many chromosomes are present in one human cell? – 92 Once the sister chromatids separate, they are considered to be individual chromosomes – How many chromatids are present in one human cell? – 0  By the end of telophase How many chromosomes are present in one nucleus within the human cell? ○ 46 chromosomes Are the nuclei identical or different? ○ identical By the end of cytokinesis How many chromosomes are present in one human cell? ○ 46 How many chromatids are present in one human cell? ○ 0 (Chromatids will not be present until after the next S phase.)  TOPIC 2: MEIOSIS ○ Reduction of chromosome number ○ Stages of meiosis ○ Crossing over & independent assortment ○ Mitosis vs. meiosis: similarities & differences ○ Nondisjunction Textbook pgs. 572-586 Meiosis Amoeba Sisters ○ https://www.youtube.com/watch?app= desktop&v=VzDMG7ke69g Meiosis ○ Meiosis: Cell division where the number of chromosomes is halved to produce sex cells. ○ Produces 4 haploid cells ○ Two divisions. ○ Humans ○ Diploid: 46 ○ Haploid: 23 Meiosis: Formation of Gametes Homologous Chromosomes: Chromosomes that have the same length and centromere position. Same genes in same locations. ○ Alleles: Alternative forms of genes. ○ Gene for eye color, allele for brown or blue eyes. ○ Autosomal Chromosomes: All of the chromosomes that don’t determine the sex of an individual. ○ Humans have 22 Pairs of autosomal chromosomes. ○ Sex Chromosomes: Pair of sex chromosomes. ○ XX: Female ○ XY: Male Two Key Outcomes of Meiosis 1. Reduction Division: formation of daughter cells with fewer chromosomes than the parent cell 2. Recombination: there is a different combination of genes (genetically distinct from each other)  Meiosis The outcome of meiosis is different than that of mitosis in three ways: 1) Produces four daughter cells rather than two 2) Daughter cells have fewer chromosomes than parent cells 3) Daughter cells have chromosomes with different combinations of genes compared to those in parent cells Phases of Meiosis ○ Two Divisions ○ Meiosis I and II ○ Normal Interphase occurs in Meiosis I, but not II.  Meiosis Phases of Meiosis – 4 Stages (prophase, metaphase, anaphase and telophase) ** there is going to be TWO complete rounds of the above phases known as: MEIOSIS I & MEIOSIS II Introduction to Meiosis ** Pay attention to the key stages and features of each stage * https://www.youtube.com/watch?v=16enC385R0w&t=6s  PROPHASE I Like in mitosis, meiosis begins with interphase, or DNA replication. Entering prophase I, then, the cell contains two pairs of homologous chromosomes… o Chromatin condenses to form chromosomes, spindle fibres form, nuclear membrane dissolves, etc. o Homologous chromosomes align (“synapsis”) for crossing over Crossing over or “mixing” of genes: Exchange of genetic material between non-sister chromatids of homologous chromosomes during Meiosis I. that results in recombinant chromosomes during sexual reproduction Chromatids are no longer identical. Increases genetic diversity of offspring. (Happens ONLY during prophase I of meiosis) METAPHASE I o Spindle fibres attach to the centromere of each chromosome o Instead of lining up in single file as they do in mitosis, chromosomes line up as homologous pairs, so that chromosomes of maternal and paternal origin will end up at opposing poles o The orientation of each pair of homologous chromosomes is independent of the orientation of the other pairs (independent assortment)  Independent Assortment: alleles of two (or more) different genes get sorted into gametes independently of one another (the allele a gamete receives for one gene does not influence the allele received for another gene) Increases gamete diversity due to number of potential chromosome combinations Genetic Variation Independent assortment of each tetrad creates , 223 or 8,388,608 combinations for one person. 70,368,744,000,000 combinations are possible after fertilization. With fertilization and crossing-over, 4,951,760,200,000,000,000,000,000,00 0 combinations are possible.  ANAPHASE I o Spindle fibres shorten, pulling homologous chromosomes apart o Sister chromatids remain together, so that each new pole has a full set of DNA  TELOPHASE I o Homologous chromosomes begin to uncoil, spindle fibres disappear o Cytoplasm is divided and a nuclear membrane forms around each new set of chromosomes o Each new cell is haploid because they contain either the maternal or paternal set of homologous chromosomes o After cytokinesis, the two daughter cells would have genetically different chromosomes after meiosis I Let’s Review Meiosis I  MEIOSIS II ▪Cells move from meiosis I to meiosis II without copying their DNA. (Interphase does NOT occur before entering prophase II) ▪Meiosis II is a shorter/simpler process than meiosis I, think of meiosis II as “mitosis for haploid cells” o Cells proceed through prophase, metaphase, anaphase, and telophase once more o The result is four haploid daughter cells with a single copy of each chromosome  Meiosis reduces the chromosome number from diploid to haploid ○ Meiosis II follows meiosis I without chromosome duplication (no interphase) ○ Each of the two haploid products enters meiosis II ○ Events in the nucleus during meiosis II Copyright © 2009 Pearson Education, Inc. Prophase II ○ Chromosomes condense ○ Nuclear membrane disintegrates ○ Centrioles migrate and form spindle/asters ○ No synapsis/crossing over ○ Events in the nucleus during meiosis II Metaphase II – Duplicated chromosomes align at the cell equator Anaphase II – Sister chromatids separate and chromosomes move toward opposite poles Copyright © 2009 Pearson Education, Inc.  Telophase II – Chromosomes have reached the poles of the cell – A nuclear envelope forms around each set of chromosomes – With cytokinesis, four haploid cells are produced Question – How many chromosomes are present in one human cell? – 23 – How many chromatids are present in one human cell? – 0 Copyright © 2009 Pearson Education, Inc. Genetic Variation ○ Meiosis ○ Creates genetically different cells. ○ Doesn’t have to rely on mutations alone for evolution. ○ Two Genetic Variations ○ Crossing Over ○ Independent Assortment ○ Genetic variation creates better chances for a species to survive. ○ The main goal of sexual reproduction is to create a larger diversity of organisms in a species. ○ Huge evolutionary advantage.  Phases of Meiosis ○ At the beginning of Meiosis II, cells are haploid. ○ Cells still contain sister chromatids. ○ Meiosis II and Mitosis are very similar. ○ Cells are haploid at end. ○ DNA is different from cell to cell.  MITOSIS MEIOSIS Parent cell Site of MEIOSIS I (before chromosome duplication) crossing over Prophase I Prophas e Tetrad formed Duplicated by synapsis of Chromosom Chromosom chromosome homologous e e (two sister chromosomes duplication 2n = 4 duplication chromatids) Chromosomes Tetrads Metaphase align at the Metaphase I align at the metaphase plate metaphase plate Anaphase Anaphase I Telophase Sister chromatids Telophase I separate during Homologous anaphase chromosomes separate (anaphase I); Haploid sister chroma- n=2 tids remain Daughter together cells of meiosis I No further 2n 2n chromosomal MEIOSIS II Daughter duplication; cells sister of mitosis chromatids separate n n n n (anaphase II) Daughter cells of meiosis II Each haploid cell formed after telophase II will proceed through cytokinesis to form gametes… In males, this process is referred to as spermatogenesis, and results in the formation of four viable sperm cells Spermatogenesis ○ Products of Meiosis are haploid gametes ○ Produces sperm  Spermatogenesis: 2n 2n n n n  Oogenesis (eggs) ○ Starts with a diploid cell ○ Unevenly divides cytoplasm (asymmetrical cytokinesis) ○ Produces one ovum  In females, the cytoplasm is not equally divided amongst gametes, resulting in a single viable ovum and three polar bodies: This process is referred to as oogenesis  Oogenesis: 2n 2n n n  Why does female gametogenesis involve unequal division of the cytoplasm? Zygote receives all the cytoplasm from the egg, so it needs as much as possible Nondisjunction ○ Failure of chromosomes to separate that results in gain or loss of chromosomes.  Nondisjunction: When things go wrong Nondisjunction during meiosis I and meiosis II have different outcomes; however, both produce gametes with either too few or too many chromosomes, resulting in either trisomy (2n+1)or monosomy (2n-1) upon fertilization. Start Video at 3:47 Warning: Some of the next slides contain images of individuals with genetic disorders. These images are meant to educate, not to make fun of an individual’s appearance.  MONOSOMY: one chromosome is lost  Turner’s Syndrome (XO) ○ Develop as a girl. ○ Physical irregularities ○ Short Stature ○ Wide neck ○ Ovaries don’t develop correctly. ○ Low hairline on back of head. ○ Minimal breast development ○ Infertile. ○ Shorter Life expectancy. ○ 1 in 5,000 females.  Klinefelter’s syndrome (XXY) ○ Develops as a male. ○ Physical irregularities ○ Absent, delayed or incomplete puberty. ○ Less muscle ○ Less facial and body hair ○ Enlarged breast tissue ○ Smaller male genitalia ○ Usually average academic capabilities. ○ Infertile. ○ 1 in 1,000 babies ○ 70% of cases go undiagnosed. TRISOMY: gaining of an extra chromosome  Incidence of Down Syndrome with maternal age: o As a woman ages, her probability of producing eggs with an extra copy of chromosome 21 increases dramatically. This is thought to happen because centromeres become “sticky” with age, meaning that nondisjunction will occur more readily o Trisomy 21 can also be caused by nondisjunction in sperm cells Cell Division and Conception of Twins ▪ While most women release only a single secondary oocyte at times another secondary oocyte can also be released ✔ IF BOTH are fertilized and implanted FRATERNAL TWINS are born ✔ IF a SINGLE zygote divides into TWO separate bodies, then IDENTICAL TWINS are born  Mitosis Meiosis ○ One Division ○ Two Divisions ○ Creates two diploid ○ Creates four cells haploid cells ○ Cells are ○ Cells are genetically genetically identical different ○ Creates somatic ○ Create germline cells cells.  TOPIC 3: ALTERNATION OF GENERATIONS ○ Reproductive strategies ○ Alternation of generations ○ Sporophyte vs. gametophyte Textbook pgs. 579-580  REPRODUCTIVE STRATEGIES ○ Mitosis is involved in asexual reproduction, ○ Meiosis is involved in sexual reproduction ○ Most organisms’ life cycles involve both processes  Reproductive Strategies The human life cycle relies on regular patterns of meiosis and mitosis. However, other organisms rely on alternative reproductive strategies… Asexual Reproduction ○ Offspring arise from and inherit the genes of a single parent ○ Does not involve meiosis, reduction division, or fertilization. ○ Types: ○ Binary fission ○ Vegetative reproduction ○ Budding ○ Fragmentation ○ Parthenogenesis  → Binary Fission o Method of reproduction utilized by bacteria o Allows for rapid growth of identical populations through asexual reproduction o offspring are genetically identical. Advantages? Disadvantages?  → Conjugation o Also utilized by bacteria o Plasmids (another source of DNA) are transferred from one cell to another through pili o Creates cells with new genetic combinations (sexual reproduction)  → Budding A form of asexual reproduction in which a complete but miniature version of the parent grows out from the parent’s body; the newly formed clone separates only once it matures Commonly utilized by metazoans such as corals, sponges, and hydra → Vegetative Reproduction New individuals are formed without the production of seeds or spores (Example formation of miniaturized plants called plantlets & reproducing plants from “cuttings”)  → Parthenogenesis A form of asexual reproduction in which an unfertilized egg develops into an adult Parthenogenesis occurs naturally in many plants, some invertebrates (Example: water fleas, aphids, stick insects, some ants, bees and parasitic wasps), & vertebrates (Example: some reptiles, amphibians, fish, very rarely birds). In bees, the queens lay unfertilized eggs (which become the drones) and fertilized eggs (which become the workers) → Spores Form of asexual reproduction which allows parents to disperse their offspring over long distances o Often dispersed by wind or water o May be haploid or diploid o Some spores are actually the product of sexual reproduction (meiosis rather than mitosis), resulting in an alternation of generations  “ALTERNATION OF GENERATIONS” The life cycle of some plants consists of two generations… 1. A diploid generation, or sporophyte 2. A haploid generation, or gametophyte Through meiosis, the sporophyte (or spore-making body) produces multiple haploid spores, which spread and develop without fertilization. Each spore grows into a plant body called the gametophyte (or gamete-making body), which produces male and female gametes. Upon fertilization, gametes develop into another sporophyte, and the cycle repeats. General model for alternation of generations:  Many plants spend the majority of their lives in one phase or the other… Conifers, for example, spend most of their lives in the diploid generation. The tree itself is this diploid sporophyte, while the cones contain the haploid gametophytes.  Rather than alternating between haploid and diploid generations, some organisms simply alternate between sexual and asexual reproduction (e.g. cnidarians): Mitosis Meiosis