Cell division is the process by which a parent cell divides into two or more daughter cells. Cell division usually occurs as part of a larger cell cycle.
1. Cell Division Mitosis & Meiosis Image: Cell Division, Wikipedia From the Virtual Cell Biology Classroom on ScienceProfOnline.com
2. Eukaryotic Cell Cycle – Cell grows. – DNA is replicated. – Mitotic cell division produces daughter cells identical to the parent. – Repeat. The timing of replication and cell division is highly regulated. Image: Cell cycle by Richard Wheeler From the Virtual Cell Biology Classroom on ScienceProfOnline.com
3. Eukaryotic Cell Cycle 2 major phases: • Interphase (3 stages) – DNA is not condensed • Mitosis (4 stages + cytokinesis) – Nuclear division & division of cytoplasm – DNA condensed Image: Cell cycle by Richard Wheeler From the Virtual Cell Biology Classroom on ScienceProfOnline.com
4. Interphase Non-dividing state with 3 sub-stages: Gap 1 – cell grows in size – organelles replicated Synthesis – replication of DNA – synthesis of proteins associated with DNA Gap 2 – synthesis of proteins associated with mitosis Image: Cell cycle by Richard Wheeler; Interphase in Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
5. Mitosis Division of somatic cells (non-reproductive cells) in eukaryotic organisms. A single cell divides into two identical daughter cells. Daughter cells have same number of chromosomes as does parent cell.
6. Packing for the move… When the cell is not dividing… • DNA molecules are in extended, uncondensed form = chromatin • Cell can only replicate and transcribe DNA when it is in the extended state. When the cell is preparing for division… • DNA molecules condense to form chromosomes prior to division. • each chromosome is a single molecule of DNA • easier to sort and organize the replicated DNA into daughter cells From the Virtual Cell Biology Classroom on ScienceProfOnline.com
7. Mitosis 4 sub-phases: 1st – Prophase 2nd – Metaphase 3rd – Anaphase 4th – Telophase followed by Cytokinesis Image: Mitosis diagram, Marek Kultys From the Virtual Cell Biology Classroom on ScienceProfOnline.com
8. 1. Prophase chromatin condensing nucleus chromosomes nucleolus Three Major Events centrioles 1. chromosomes condense 2. spindle fibers form 1. (spindle fibers are specialized microtubules radiating out from centrioles) 3. chromosomes are captured by spindle From the Virtual Cell Biology Classroom on ScienceProfOnline.com
9. 2. Metaphase • chromosomes align along the equator of the cell, with one chromatid facing each pole centrioles chromosomes spindle fibers Images: Metaphase drawing, Henry Gray's Anatomy of the Human Body; Metaphase Onion Cell Drawing & Photo, Source Unknown
10. 3. Anaphase • sister chromatids separate • spindle fibers attached to kinetochores shorten and pull chromatids towards the poles. • free spindle fibers lengthen and push the poles of the cell apart Images: Anaphase drawing, Henry Gray's Anatomy of the Human Body; Anaphase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
11. 4. Telophase • spindle fibers disintegrate • nuclear envelopes form around both groups of chromosomes • chromosomes revert to their extended state • cytokinesis occurs, enclosing each daughter nucleus into a separate cell Images: Telophase drawing, Henry Gray's Anatomy of the Human Body; Telophase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
12. Cytokinesis – Plant vs. Animal Cell • Plant cells undergo cytokinesis by forming a cell plate between the two daughter nuclei. • Animal cells undergo cytokinesis through the formation of a cleavage furrow. A ring of microtubules contract, pinching the cell in half. Images: Telophase drawing, Henry Gray's Anatomy of the Human Body; Ciliate dividing, TheAlphaWolf; Telophase Onion Cell Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com
13. Genetics Terminology SEXually reproducing eukaryotes have two types of body cells… Made you look! 1. somatic cells 2. sex cells (a.k.a. gametes, germline) Image: Superficial human anatomy, Mikael Häggström& Rainer Zenz; Sperm & egg, Wikipedia From the Virtual Cell Biology Classroom on ScienceProfOnline.com
14. What is cell division of gametes called? Meiosis - A single germ cell divides into four unique daughter cells. - Daughter cells have half the # of chromosomes as parent cell, so they are considered haploid. Image: Overview of Meiosis, National Institutes of Health From the Virtual Cell Biology Classroom on ScienceProfOnline.com
15. Genetics Terminology: Ploidy Refers to the number of sets of chromosomes in cells. ● Haploid – one copy of each chromosome – designated as “n”, the number of chromosomes in one “set” – gametes ● Diploid – two sets of chromosomes (two of each chromosome) – designated as “2n” – somatic cells Diploid organisms receive one of each type of chromosome from female parent (maternal chromosomes) and one of each type of chromosome from male parent (paternal chromosomes) From the Virtual Cell Biology Classroom on ScienceProfOnline.com
16. Genetics Terminology: Homologues Chromosomes exist in homologous pairs in diploid (2n) cells. Exception: Sex chromosomes (X, Y). All other chromosomes (autosomes) have homologues. From the Virtual Cell Biology Classroom on ScienceProfOnline.com
17. Karyotype • Q: How many homologous pairs are in each karyotype? • Q: How is the bottom karyotype different from the top two? From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Karyotype, National Human Genome Research Institute
18. Sexual Reproduction • Fusion of two gametes to produce a single zygote. • Introduces greater genetic variation, allows genetic recombination. • Zygote has gametes from two different parents (except in cases of self- fertilizing organisms). Rose + Greg = Steven Images: Rose, Greg, and Steven, Steven Universe From the Virtual Cell Biology Classroom on ScienceProfOnline.com
19. Sexual reproduction in humans … • At fertilization, 23 chromosomes are donated by each parent. (total = 46 or 23 pairs). • Gametes (sperm/ova): – Contain 22 autosomes and 1 sex chromosome. – Are haploid (haploid number “n” = 23 in humans). • Fertilization results in diploid zygote. – Diploid cell; 2n = 46. (n = 23 in humans) • Q: Most cells in the body are produced through what type of cell division? (Remember, only gametes are produced through meiosis) Image: Superficial human anatomy, Mikael Häggström& Rainer Zenz; Sperm & egg, Wikipedia From the Virtual Cell Biology Classroom on ScienceProfOnline.com
20. Meiosis - Sex Cell (Gamete) Formation In meiosis, there are 2 divisions of the nucleus: meiosis I & meiosis II Image: Overview of Meiosis, National Institutes of Health From the Virtual Cell Biology Classroom on ScienceProfOnline.com
21. From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Meiosis diagram, Marek Kultys
22. Meiosis & Sexual Reproduction Life Cycle * Mitosis * * From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Animal Life Cycle, Dr. T’s Bio 328 Genetics
23. Genetic Variation in Diploid Organisms Fusion of sperm and egg results in unique …but not only because the young are a product of two individuals with different genetic makeup. Meiosis also “shuffles” the genes so that the an individual’s gametes are genetically different from one another. How is this shuffling accomplished? From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Meiosis diagram, Marek Kultys
24. Genetic shuffling of Meiosis I In addition to a new combination of chromosomes resulting from fertilization, there are also events in Meiosis I that shuffle the genes. 1. Crossing over in Prophase I. 2. Independent assortment in Metaphase I. From the Virtual Cell Biology Classroom on ScienceProfOnline.com
25. Crossing Over • Homologues break at identical locations, then rejoin opposite partners. • This creates new combinations of the alleles on each chromosome. • Occurs randomly several times on every chromosome. • Results in mixing of the genes you inherited from your parents. From the Virtual Cell Biology Classroom on ScienceProfOnline.com
26. Independent Assortment
27. Variation from genetic recombination • Independent assortment of chromosomes – meiosis introduces genetic variation – gametes of offspring do not have same combination of genes as gametes from parents • random assortment in humans produces 223 (8,388,608) different combinations in gametes new gametes from Mom from Dad offspring made by offspring
28. Mitosis vs. Meiosis • 2n • 1n • Daughter cells different • Clone from parent cell and from • Same genetic each other. information in parent • Daughter cells have ½ the cell and daughter cell. number of chromosomes • Give me another one as somatic cell. just like the other one! • Shuffling the genes (Mix it up!) From the Virtual Cell Biology Classroom on ScienceProfOnline.com
29. Image: Mitosis diagram & Meiosis diagram, Marek Kultys From the Virtual Cell Biology Classroom on ScienceProfOnline.com
30. Drawing and Labeling Chromosomes Centromere Sister Sister Chromatid Chromatid Unreplicated Uncondensed Replicated Chromosome Uncondensed Chromosome (chromatin) (chromatin) From the Virtual Cell Biology Classroom on ScienceProfOnline.com
31. Drawing & Labeling Homologous Chromosomes Unreplicated, Replicated, Condensed, Condensed, Homologous Chrom Homologous osomes Chromosomes From the Virtual Cell Biology Classroom on ScienceProfOnline.com
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