Eukaryotic Cell Cycle & Cell Division (Notes)

Chapter 14 – How Eukaryotic Cells Sort and Transmit Chromosomes: Mitosis and Meiosis Chapter Outline 1. The eukaryotic cell cycle 2. Mitotic cell division 3. M...

Chapter 14 – How Eukaryotic Cells Sort and Transmit Chromosomes: Mitosis and Meiosis Chapter Outline 1. The eukaryotic cell cycle 2. Mitotic cell division 3. Meiosis 4. Sexual reproduction 5. Variations in chromosome structure and number Remember blue font color marks important ideas and bold marks terms to master 14.1 The Eukaryotic Cell Cycle Section 14.1 Learning Outcomes 1. Describe how sets of chromosomes are examined microscopically 2. Define the following terms and sketch examples of each: sister chromatids, diploid cell, haploid cell, homologous chromosomes 3. Describe the phases of the eukaryotic cell cycle 4. Explain how cyclins, cdks, and checkpoints regulate progression through the eukaryotic cell cycle 14.1 The Eukaryotic Cell Cycle Cell division, the reproduction of cells, is a highly regulated process The cell cycle is a series of events that results in cell division; it is highly regulated so cell division occurs at the appropriate time Loading… 14.1 The Eukaryotic Cell Cycle Chromosomes Are Inherited in Sets and Occur in Homologous Pairs When cells prepare to divide, the chromosomes become compact enough to be seen with a light microscope A karyotype reveals the number, size, and form of chromosomes in an actively dividing cell  14.1 The Eukaryotic Cell Cycle Chromosomes Are Inherited in Sets and Occur in Homologous Pairs Human genome: 23 pairs 46 total 22 autosomal pairs 1 sex pair Loading… Diploid Haploid 14.1 The Eukaryotic Cell Cycle Chromosomes Are Inherited in Sets and Occur in Homologous Pairs Homologs / Homologous chromosomes Same DNA sequences in the same order Packages of genes Gene locus Two Alleles at each Gene Locus Sets up a “back up” system in case you inherit a “nonfunctional” copy from one parent This Photo by Unknown Author is licensed under CC BY-SA  14.1 The Eukaryotic Cell Cycle Dividing cells progress through a series of phases Cells may also exit the cycle and remain in G0, a non- dividing phase 14.1 The Eukaryotic Cell Cycle The Cell Cycle Is a Series of Phases That Lead to Cell Division G1 (first gap) phase is a period when cells typically grow; environmental conditions and signaling molecules can direct a cell to progress through the cell cycle S (synthesis) phase is the period of DNA replication; after replication the 2 duplicate copies of each chromosome stay joined to each other and are called sister chromatids G2 (second gap) phase is a period when a cell synthesizes the proteins necessary for chromosome sorting and cell division; some growth may occur M phase is a period of division; mitosis divides one cell nucleus into two nuclei and cytokinesis divides the cytoplasm 14.1 The Eukaryotic Cell Cycle Cyclins and Cyclin-Dependent Kinases Advance a Cell through the Cell Cycle 14.1 The Eukaryotic Cell Cycle Cyclins and Cyclin-Dependent Kinases Advance a Cell through the Cell Cycle Checkpoints regulate the advancement of a cell through the cell cycle 14.2 Mitotic Cell Division Section 14.2 Learning Outcomes 1. Explain how the replication of eukaryotic chromosomes produces sister chromatids 2. Describe the structure and Loading… function of the spindle apparatus 3. Name the phases of mitosis and describe the key events that occur during each phase 4. Sketch the phases of mitosis for a diploid cell with a total of 8 chromosomes (4 homologous pairs) 14.2 Mitotic Cell Division During mitotic cell division, a cell divides to produce two new cells that are genetically identical to the original cell (and genetically identical to each other) Original cell is the mother cell; new cells are daughter cells Process involves mitosis and cytokinesis Mitotic divisions are used for asexual reproduction and for growth and development of multicellular organisms 14.2 Mitotic Cell Division Eukaryotic Chromosomes Are Replicated and Compacted to Produce DNA is replicated in Pairs Called S phase beforeSister Chromatids Mitosis. The copy is “stapled” to the original. This will be helpful when moving chromosomes around in mitosis. The identical copies are called sister chromatids. One replicated chromosome contains two sister chromatids. 14.2 Mitotic Cell Division The Spindle Apparatus Organizes and Sorts Chromosomes During Cell Division The spindle apparatus organizes and sorts the chromosomes during cell division; it is composed of microtubules In animal cells, microtubule growth and organization start at two centrosomes (aka microtubule organizing centers) A single centrosome duplicates during interphase Centrosomes separate from each other during mitosis and each defines a pole of the spindle apparatus Centrosomes in animal cells have centrioles; however centrioles are not found in many other eukaryotic species 14.2 Mitotic Cell Division The Transmission of Chromosomes in Eukaryotes Requires a Sorting Process Known as Mitosis Big goal of Mitosis: Line up those replicated chromosomes… Snap them apart, sending one chromatid to one daughter cell and the other chromatid to the other daughter. 14.2 Mitotic Cell Division The Transmission of Chromosomes in Eukaryotes Requires a Sorting Process Known as Mitosis 14.2 Mitotic Cell Division The Transmission of Chromosomes in Eukaryotes Requires a Sorting Process Known as Mitosis 14.2 Mitotic Cell Division The Transmission of Chromosomes in Eukaryotes Requires a Sorting Process Known as Mitosis The process of cytokinesis, which divides the cytoplasm to produce 2 distinct daughter cells, occurs differently in plant and animal cells In animal cells, a cleavage furrow forms which constricts (like a drawstring) to separate the cells In plant cells, vesicles from the Golgi move along microtubules to the center of the cell and coalesce to form a cell plate New cell wall will form from the cell plate 14.3 Meiosis Section 14.3 Learning Outcomes 1. Describe the processes of synapsis and crossing over 2. Name the phases of meiosis and describe the key events that occur during each phase 3. Sketch the phases of meiosis for a diploid cell with a total of 8 chromosomes (4 homologous pairs) 4. Compare and contrast mitosis and meiosis, focusing on key steps that account for the different outcomes of these two processes 14.3 Meiosis and Sexual Reproduction In humans, specialized cells within the reproductive organs (ovaries and testes) undergo Meiosis to produce gametes (sperm and egg cells) 14.3 Meiosis and Sexual Reproduction Meiosis I Separates Homologous Chromosomes Like mitosis, meiosis begins after a cell has progressed through the G1, S, and G2 phases of the cell cycle Like mitosis, the sorting of chromosomes during meiosis occurs as a series of stages called prophase, prometaphase, metaphase, anaphase, and telophase Meiosis I separates homologous chromosomes from each other The pairing of homologous chromosomes is a distinguishing feature of meiosis Meiosis II separates sister chromatids from each other 14.3 Meiosis and Sexual Reproduction Meiosis I Separates Homologous Chromosomes 14.3 Meiosis and Sexual Reproduction Meiosis I Separates Homologous Chromosomes Cytokinesis follows meiosis I Meiosis I has produced 2 haploid cells; these cells do not have pairs of homologous chromosomes anymore There is no S phase between meiosis I and meiosis II Meiosis II separates sister chromatids during anaphase whereas meiosis I separates bivalents during anaphase 14.3 Meiosis and Sexual Reproduction Meiosis II Separates Sister Chromatids The sorting events of meiosis II include prophase II, prometaphase II, metaphase II, anaphase II, telophase II 14.3 Meiosis and Sexual Reproduction Mitosis and Meiosis Differ in a Few Key Steps Mitosis produces 2 diploid daughter cells that are genetically identical Meiosis produces 4 haploid daughter cells that are genetically diverse 14.4 Sexual Reproduction Section 14.4 Learning Outcomes 1. Explain how meiosis enhances genetic diversity among gametes 2. Compare and contrast the advantages and disadvantages of sexual reproduction 3. Distinguish between diploid- dominant, haploid-dominant, and alternation of generations life cycles 14.4 Sexual Reproduction Sexual Reproduction Provides a Mechanism for Greater Genetic Diversity in Offspring Sexual reproduction involves two haploid gametes (generated by meiosis) fusing together to form a diploid cell called a zygote A potential advantage of sexual reproduction is that is allows for greater genetic variation in offspring (which can be acted upon by natural selection, allowing faster adaptation to the environment) Meiosis enhances genetic diversity through random alignment of homologous chromosomes and though crossing over For humans there are over 8 million (223) possibilities for the alignment of the chromosomes For any diploid species, the number of random alignments equals 2n where n equals the number of chromosomes per set Compared with asexual reproduction, disadvantages of sexual reproduction include need for two types of gametes, specialized body parts, and ability to find mates (all of which require energy) 14.4 Sexual Reproduction Sexually Reproducing Species Produce Haploid and Diploid Cells at Different Times in Their Life Cycles A life cycle is a sequence of events that produces another generation of organisms For sexually reproducing organisms, the life cycle involves an alternation between haploid and diploid states Different organisms vary in regards to the amount of time they spend in haploid versus diploid states Most animal species are classified as diploid-dominant species, meaning most of the life cycle is spent in the diploid state 14.4 Sexual Reproduction Sexually Reproducing Species Produce Haploid and Diploid Cells at Different Times in Their Life Cycles Many fungi and some protists are haploid-dominant species, meaning most of the life cycle is spent in a haploid state The “mature” multicellular organism is composed of haploid cells Loading…  14.4 Sexual Reproduction Sexually Reproducing Species Produce Haploid and Diploid Cells at Different Times in Their Life Cycles Plants and some algae exhibit an alternation of generations, spending similar amounts of time in diploid and haploid states The sporophyte is a multicellular diploid organism and the gametophyte is a multicellular haploid organism  Let’s practice Question 8 A type of organism that exhibits alternation of generations is ) an animal ) a mammal ) a fungus ) a plant ) both a and b are correct 14.5 Variation in Chromosome Structure and Number Section 14.5 Learning Outcomes 1. Describe how chromosomes vary in size, centromere location, and number 2. Identify the 4 ways that the structure of chromosomes can be changed 3. Compare and contrast changes in the number of sets of chromosomes and changes in the number of individual chromosomes 4. Sketch examples of the following phenomena: triploid, tetraploid, monosomy, trisomy 14.5 Variation in Chromosome Structure and Number Variations in chromosome structure and number can have major effects on organisms Several human diseases are caused by chromosomal changes Changes in chromosome number and structure have been important in the evolution of new species Some types of chromosome variation are normal and some are abnormal 14.5 Variation in Chromosome Structure and Number Natural Variation Exists in Chromosome Structure and Number Chromosome composition within a given species tends to remain relatively constant, although composition differs across species Humans 2 sets of 23 chromosomes (total of 46) Dog 2 sets of 39 chromosomes (total of 78) Fruit fly 2 sets of 4 chromosomes (total of 8) Tomato 2 sets of 12 chromosomes (total of 24) Features used to classify and describe chromosomes include size, location of the centromere, and banding patterns 14.5 Variation in Chromosome Structure and Number Mutations Can Alter Chromosome Structure Banding patterns of eukaryotic chromosomes are used to detect changes in chromosome structure that occur as a result of mutation Chromosomal mutations involve breaking and rejoining the chromosomes; mutations are classified as deletions, duplications, inversions, and translocations Deletions and duplications change the total amount of genetic material in a chromosome A deletion removes part of a chromosome A duplication causes part of the chromosome to be repeated 14.5 Variation in Chromosome Structure and Number Mutations Can Alter Chromosome Structure Inversions and translocations are chromosomal rearrangements An inversion changes the direction of the genetic material along a single chromosome A translocation attaches a segment of one chromosome to a different chromosome Translocations can be simple or reciprocal 14.5 Variation in Chromosome Structure and Number Variation Occurs in the Number of Chromosome Sets and the Number of Individual Chromosomes Variations in chromosome number can be categorized based on: The number of sets of chromosomes The number of particular chromosomes within a set Organisms that are euploid have chromosomes that occur in one or more complete sets Diploid (2n) 2 complete sets Polyploid 3 or more complete sets Triploid (3n) 3 complete sets Tetraploid (4n) 4 complete sets 14.5 Variation in Chromosome Structure and Number Variation Occurs in the Number of Chromosome Sets and the Number of Individual Chromosomes Aneuploidy is different than euploidy refers to an alteration in the number of just one chromosome An extra copy of a particular chromosome causes trisomy (2n +1) Lacking a copy of a chromosome causes monosomy (2n -1) 14.5 Variation in Chromosome Structure and Number Variation Occurs in the Number of Chromosome Sets and the Number of Individual Chromosomes A change in chromosome number can occur because of nondisjunction, the abnormal sorting of chromosomes during cell division Nondisjunction during meiosis can generate aneuploid gametes that have too many or too few chromosomes 14.5 Variation in Chromosome Structure and Number Changes in Chromosome Number Have Important Consequences In animals, deviations from diploidy are usually lethal A few exceptions: male bees are haploid whereas female bees are diploid, and there are some polyploid species of amphibians and reptiles There are some cases of survivable aneuploidies Typically trisomies for smaller chromosomes with fewer genes 14.5 Variation in Chromosome Structure and Number Changes in Chromosome Number Have Important Consequences In animals, deviations from diploidy are usually lethal Why? for many genes the level of gene expression correlates with the number of gene copies 3 copy (instead of 2) 150% of the normal amount of product, which typically interferes with normal cell function There are some cases of survivable aneuploidies Typically trisomies for smaller chromosomes with fewer genes 14.5 Variation in Chromosome Structure and Number Changes in Chromosome Number Have Important Consequences In contrast to animals, plants commonly exhibit polyploidy which is important in agriculture Polyploid plants often have characteristics that are helpful to humans large, robust, adaptable Ex: the wheat we use to make bread is hexaploid (6n)  Let’s practice Question 10 A person who is born with Patau Syndrome carries 3 copies of chromosome 13 in his or her cells. Which of the following terms is an inaccurate description of this genetic condition? ) euploid ) trisomy 13 ) triploid ) Aneuploid ) A, B, C ) A, D ) B and C