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Lecture6BIO155 - BIO155 Cellular Reproduction Dr Jessica...

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Unformatted text preview: BIO155 Cellular Reproduction Dr. Jessica Pamment Overview Overview • • • • Relevance of cellular reproduction The cell cycle Mitosis Meiosis Functions of Cell Division • In unicellular organisms a single division produces two new organisms • In multicellular organisms many rounds of division are required to make a new individual • Division required throughout life of multicellular organisms to replace old/damaged cells The Functions of Cell Division The 100 µm 200 µm 20 µm (a) Reproduction (b) Growth and development (c) Tissue renewal Asexual Reproduction by Mitosis Asexual Reproduction by Mitosis Asexual reproduction Asexual Reproduction Asexual Reproduction • Organisms that reproduce by asexual reproduction make exact copies of themselves reproduction • Only mitosis takes place during asexual • Takes place in prokaryotes, unicellular eukaryotes and some multicellular organisms • Produces clones (genetically identical individuals) Asexual Reproduction in hydra 0.5 mm Parent Bud (a) Hydra Eukaryotic Chromosomes • Humans have approx. 21,000 genes/cell • Genes are located on chromosomes • Humans contain 46 chromosomes in each cell (except gametes, these contain 23) Eukaryotic Chromosomes Eukaryotic 20 µm The amazing feats of DNA packaging! • In a mammalian cell…. • The DNA, if stretched out, is 2 m in length • The nucleus is approx. 6 µ m • This means the DNA is 333, 333 times longer than the nucleus is in diameter!!! DNA Packaging DNA Packaging in a eukaryotic chromosome Level 1 Level 2 Level 3 Levels of DNA Packaging • DNA is wrapped around proteins to make chromatin • Chromatin is coiled further into chromosomes Chromosome Chromosome Duplication and Distribution The Cell Cycle The Cell Cycle • Is the life of a cell from when it is just formed until it undergoes its own division • Duration varies from between organisms Phases of the Cell Cycle Phases of the Cell Cycle • i. ii. • Mitotic phase: Mitosis (division of nucleus) Cytokinesis (division of cytoplasm) Interphase: accounts for 90% cycle Cell grows & chromosomes duplicate The The Eukaryotic Cell Cycle Chromosome Changes During Cell Division Chromosome Mitosis in an Animal Cell Mitosis G2 of Interphase Prophase Prometaphase Metaphase Anaphase Telophase and Cytokinesis Cytokinesis in animal cells 100 µm Cleavage furrow Contractile ring of microfilaments Daughter cells (a) Cleavage of an animal cell (SEM) Vesicles forming cell plate Wall of parent cell Cell plate 1 µm New cell wall Daughter cells (b) Cell plate formation in a plant cell (TEM) Cytokinesis in animal/plant cells • http://video.search.yahoo.com/search/vide o;_ylt=A0SO8Zr1AbNMkHUA3sP7w8QF;_ ylu=X3oDMTBncGdyMzQ0BHNlYwNzZW FyY2gEdnRpZAM­? p=cleavage+furrow+in+animal+cells&fr=yf p­t­892&ei=utf­8&n=21&tnr=18&y=Search Video of mitosis Video of mitosis • http://video.search.yahoo.com/video/play? p=mitosis&ei=UTF­8&fr=yfp­t­ 203&tnr=21&vid=000114826801 Mitosis in Plant Cell Mitosis Nucleus Chromatin condensing Chromosomes Cell plate 10 µm 1 Prophase 2 Late prophase 3 Metaphase 4 Anaphase 5 Telophase Control of Eukaryotic Cell Cycle Control of Eukaryotic Cell Cycle • Regulation is at the molecular level • Signaling molecules in the cytoplasm control the cell cycle • The cell cycle is regulated at certain checkpoints by both internal and external signals phases • Major checkpoints found at G1, G2, and M G1 checkpoint G1 Control system S M G2 M checkpoint G2 checkpoint Cancer cells Cancer cells • Have defective checkpoints • Lack density­dependent inhibition • Lack anchorage dependence • Can divide indefinitely with sufficient nutrient supply • Single cell undergoes transformation transformed cell, it can proliferate Cancer Development Cancer Development • If body’s immune system doesn’t destroy • Tumor is mass of abnormal cells • Benign tumor­ cells remain in original site, is not aggressive • Malignant tumor­ cells become invasive and patient has cancer The Growth and Metastasis of a Malignant Breast Tumor Tumor Cancer Treatments Cancer Treatments • Surgery • Radiation therapy for localized tumors • Chemotherapy for metastatic tumors­ uses drugs to destroy cancer cells Half of all Americans will develop cancer during their lifetime. Cancer Prevention and Survival Cancer Prevention and Survival • Cancer can strike everyone • Some people are genetically predisposed • Lifestyle can reduce your chances • Regular checkups for prevention Biology and Society • The recent availability of genetic tests for susceptibility to some types of cancer has led some patients to take extreme measures, such as having a mastectomy when there is a risk, though not a certainty, of developing breast cancer. Issues to consider • Is the doctor responsible for educating the patient about all of the preventive and diagnostic measures? • Should the patient’s wishes always be followed, regardless of the outcome? • How accurate would the testing have to be for you to decide to go ahead with a mastectomy? Summary Summary • Cell division results in two genetically identical daughter cells • Cell division is used by unicellular organisms to reproduce and by multicellular organisms to grow and repair tissues and mitotic phases • The cell cycle consists of the interphase G1 Cytokinesis Mitosis MITOTIC (M) PHASE G2 S Prophase Telophase and Cytokinesis Anaphase Metaphase Prometaphase Summary Summary • The eukaryotic cell cycle is regulated by a molecular control system • Checkpoints are found at 3 different phases • Loss of cell cycle controls results in cancer cells Mitosis and Meiosis • The type of cell division responsible for asexual reproduction is MITOSIS • The type of cell division responsible for the formation of gametes (egg and sperm) in sexually reproducing organisms is called MEIOSIS BIO155 Meiosis Dr. Jessica Pamment Fig. 8-10 Overview Overview • Role of meiosis in sexual reproduction • Comparison of meiosis and mitosis • What happens when meiosis goes wrong • Genetic variation produced in sexual life cycles contributes to evolution Sexual Reproduction Sexual Reproduction • Parents pass on genes to their offspring as a result of fertilization of their gametes phenotype • The inherited genes result in the observed • Genes are passed on in gametes Chromosomes in Human Cells Chromosomes in Human Cells • Somatic cells have 46 chromosomes, 23 pairs • Each chromosome pair is a made up of 2 homologous chromosomes • Set of chromosomes is made up of a pair of sex chromosomes and 22 pairs of autosomes • Gametes have 23 chromosomes Karyotyping Karyotyping APPLICATION TECHNIQUE 5 µm Pair of homologous replicated chromosomes Centromere Sister chromatids TECHNIQUE 5 µm Pair of homologous replicated chromosomes Centromere Sister chromatids One duplicated chromosome Terminology Terminology • Number of chromosomes in a single set n • Cell with two chromosome sets is a diploid • Diploid number for humans is 2n= 46 • Gametes contain a single set, n • Gametes are haploid cells • Each sexually reproducing species has a characteristic diploid and haploid number Describing Chromosomes Describing Chromosomes Key 2n = 6 Maternal set of chromosomes (n = 3) Paternal set of chromosomes (n = 3) Two sister chromatids Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes The Human Life Cycle Haploid gametes (n = 23) Egg cell n n Sperm cell MEIOSIS FERTILIZATION Multicellular diploid adults (2n = 46) MITOSIS and development 2n Diploid zygote (2n = 46) Key Haploid (n) Diploid (2n) Meiosis Meiosis • A form of cell division • Preceded by replication of chromosomes • Consists of two consecutive cell divisions, meiosis I and II • Results in four daughter cells, each with one set of chromosomes Meiosis Meiosis Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Diploid cell with replicated chromosomes Meiosis Meiosis Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Diploid cell with replicated chromosomes Meiosis I 1 Homologous chromosomes separate Haploid cells with replicated chromosomes Meiosis Meiosis Interphase Homologous pair of chromosomes Chromosomes replicate Homologous pair of replicated chromosomes Diploid cell with replicated chromosomes Meiosis I 1 Homologous chromosomes separate Meiosis I I 2 Sister chromatids separate Haploid cells with unreplicated chromosomes Mechanisms of Genetic Variation in Mechanisms of Genetic Variation in Sexually Reproducing Organisms 1. Independent Assortment 1. Crossing Over 1. Random Fertilization The Meiotic Division of an Animal Cell The Meiotic Division of an Animal Cell Meiosis I: separates homologs Meiosis II: separates chromatids Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Summary of Meiosis Summary of Meiosis • Chromosome sets reduced from diploid to haploid • The two stages of cell divisions produces four haploid daughter cells • During meiosis I homologs are separated • During meiosis II sister chromatids are separated • Genetic variation introduced by crossing over MITOSIS Parent cell Stage 1 Chromosome replication 2n = 6 MEIOSIS Chiasma MEIOSIS I Stage 1 Homologous chromosome pair Chromosome replication Stage 2 Stage 2 Stage 3/4 Daughter cells of meiosis I 2n Daughter cells of mitosis 2n Stage 3/4 Haploid n=3 MEIOSIS I I n n n n Daughter cells of meiosis I I Significance of Meiosis Significance of Meiosis • Meiosis introduces genetic variation into a population and thus contributes to evolution • Meiosis results in reshuffling of alleles • Alleles are different versions of a gene When Meiosis goes Wrong When Meiosis goes Wrong • Meiotic spindle distributes chromosomes to daughter cells • Members of a chromosome pair can fail to separate • Results in gametes with abnormal numbers of chromosomes Fertilization after failure of chromosomes to separate in mother mother Maternal age and Down Syndrome Maternal age and Down Syndrome Down Syndrome Down Syndrome • A trisomy: extra chromosome 21 • Affects 1 out of every 700 children • Characteristic facial features; heart defects; short stature Trisomy 21 and Down Syndrome Trisomy Down Syndrome Down Syndrome Triploidy Triploidy Abnormal number of sex Abnormal number of sex chromosomes • Has less of an effect than abnormal number of autosomes • Y chromosome very small • Cells normally operate with only one functioning X chromosome Turner Syndrome (X0) Summary Summary • Asexual reproduction produces identical daughter cells by mitosis • Sexual reproduction combines sets of genes from different parents forming genetically diverse organisms sets from diploid to haploid: it is the basis of sexual reproduction • Meiosis reduces the number of chromosome Summary • Meiosis consists of two cell divisions which results in four haploid daughter cells • Genetic variation is introduced during meiosis due to independent assortment of chromosomes, crossing over, random fertilization F H Biology and Society • As women age, the cells in their ovaries that ultimately ;produce eggs also age. The older a woman is when she becomes pregnant the older that egg cell is and the more likely it is that chromosomal damage has occurred. IF this is the caseand th embryo has a chromosomal abnormality, the mother’s system may spontaneously abort; Biology and Society contd….. • However, the aborting mechanism also becomes defective with age. This is one reason why older women are more likely to have children born with birth defects than younger women. At menopause women stops releasing eggs. reproductive technology to have their own biological child? • What do you think of older women using Issues to consider…. • How risky is pregnancy at an older age? • If the body has naturally stopped releasing eggs, should this be overridden by technology? • How likely is it that the child will have a birth defect? • How expensive is the technology? Video of meiosis Video of meiosis • http://www.johnkyrk.com/meiosis.html ...
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