Chapters 8 & 9
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Date Created: 03/11/15
Chapter 8 part of 11 What Cell Reproduction Accomplishes Reproduction 0 May result in the birth of new organisms o More commonly involves the production of new cells When a cell undergoes reproduction or cell division two daughter cells are produced that are genetically identical to each other and the parent cell Before a parent cell splits into two it duplicates its chromosomes the structures that contain most of the organism s DNA During cell division each daughter cell receives one set of chromosomes Cell division plays important roles in the lives of organisms o Replaces damaged or lost cells 0 Permits growth 0 Allows for reproduction In asexual reproduction mitosis 0 Single celled organisms reproduce by simple cell division 0 There is no fertilization of an egg by a sperm 0 Some multicellular organisms such as sea stars can grow new individuals from fragmented pieces 0 Growing a new plant from a clipping is another example 0 The lone parent and its offspring have identical genes 0 Mitosis is the type of cell division responsible for Asexual reproduction Growth and maintenance of multicellular organisms Sexual Reproduction o Requires fertilization of an egg by a sperm using a special type of cell division called meiosis o Sexually reproducing organisms use Meiosis for reproduction Mitosis for growth maintenance The Cell Cycle and Mitosis In a eukaryotic cell 0 Most genes are located on chromosomes in the cell nucleus some are found in the mitochondria o A few genes are found in DNA in mitochondria and chloroplasts Each eukaryotic chromosome contains one very long DNA molecule typically bearing thousands of genes The number of chromosomes in a eukaryotic cell depends on the species 0 Humans have 46 chromosomes Chromosomes o Are made of chromatin a combination of DNA and protein molecules 0 Are not visible in a cell until cell division occurs Human Chromosome Number Human somatic cells have 46 chromosomes 0 All cells except reproductive cells 0 Two sets of 23 one from each parent Human reproductive cells sperm and egg cells have 23 chromosomes 0 The products of meiosis Before a cell divides it duplicates all of its chromosomes resulting in two copies called sister chromatids Sister Chromatids are joined together at a narrow waist called the centromere One chromosome can have one arm or it can have 2 sister chromatid arms It is still considered 1 chromosome until the chromatids separate The Cell Cycle Eukaryotic cells that divide undergo an orderly sequence of events called the cell cycle The cell cycle consists of two distinct phases 0 Interphase Cell spends 90 of the time Cell performs its normal functions Cell doubles everything in its cytoplasm Cell grows in size 0 Mitotic phase 10 of the time Mitosis or Nuclear Division consists of four distinct phases 0 Prophase I and Prophase II o Metaphase spindle o Anaphase daughter chromosomes 0 Telophase and Cytokinesis nuclear envelope forming and cleavage furrow Cytokinesis typically occurs during Telophase divides the cytoplasm and is different in plant and animal cells n Cleavage furrow occurs in eukaryotic cells a Cell plate occurs in prokaryotic cells Gene p53 codes for a protein that normally helps suppress the formation of tumors Cell Cycle Regulation Normal growth in plants and animals requires careful regulation 0 Skin cells divide frequently throughout life but liver cells divide only when needed to 0 Some specialized cells do not divide at all such at nerve cells Regulation is at the molecular level 0 Cancer cells are not regulated normally Normal plant and animal cells have a cell cycle control system 0 Proteins that integrate information and send stop or go aheadquot signals at key points in the cycle Both plant and animal cells can become cancerous 0 Means the cells are growing out of control Cancer A disease of the cell Cancer cells can form tumors 0 Abnormally growing masses of cells If a tumor is malignant o It can spread to other parts of the body 0 A person with malignant cancer cells is said to have cancer Benign not cancerous Cancer cells divide excessively Spread from a malignant tumor Metastasis is the spread of cancer Transformation A cell that is no longer responding to growth controls is said to be transformed Usually transformed cells are destroyed by the immune system 0 If not a tumor forms A benign tumor the cells remain at the original site A malignant tumor the cells can spread to neighboring tissues or other parts of the body Types of Cancer Named according to where they originate 4 main categories 0 Carcinoma in external or internal coverings intestine o Sarcoma in support tissues muscle or bone 0 Leukemia in the bone marrow o Lymphoma in the lymph glands The Genetic basis of cancer Cancercausing viruses often carry specific genes called oncogenes Protooncogenes o Are normal genes that can become oncogenes o Are found in many animals 0 Code for growth factors that stimulate cell division For a protooncogene to become and oncogene a mutation must occur in the cells DNA 0 Mutation within the gene 0 Multiple copies of the gene 0 Gene moved to new DNA position under new controls Tumorsuppressor genes 0 Inhibit cell division 0 Prevent uncontrolled cell growth 0 May be mutated and contribute to cancer 0 The p53 protein senses DNA damage and can halt progression of the cell in G1 It also forces damaged cells to undergo apoptosis programmed suicide Chapter 9 Gregor Mendel First person to analyze patterns of inheritance Deduced the fundamental principle of genetics Studied garden sweet pea 0 These plants are easily manipulated 0 They can selffertilize He created truebreeding varieties of plants Then crossed two different truebreeding varieties creating hyb ds The offspring from these crosses are called the first filial or F1 generation 0 Four characteristics of a good genetics research model organism Readily available Easily manipulated Short generation time Low cost Monohybrid Crosses A cross between parent plants that differ in only one characteristic Mendel s four hypotheses There are alternative forms of genes the units that determine heritable traits For each inherited character an organism inherits two alleles one from each parent If the two alleles of an inherited pair differ then one determines the organisms appearance and is called the dominant allele the other has no noticeable effect on the organism s appearance and is called the recessive allele A sperm or egg carries only one allele for each inherited character because the two members of an allele pair separate from each other during the production of gametes independent assortment Genetic Alleles and Homologous Chromosomes Homologous chromosomes 0 Have genes at a specific loci 0 Have alleles of a gene at the same locus Genotype 0 PP homozygous for the dominant allele 0 pp homozygous for the recessive allele 0 Pp heterozygous Homozygous when an organism has identical alleles for a gene Heterozygous when an organism has different alleles for a gene Phenotype an organism s physical traits Genotype an organisms genetic makeup there should be two copies of each gene Testcross a mating between an individual of unknown genotype and a homozygous recessive individual Multifactorial Disorders Many diseases have a genetic component and a significant environmental components ex Heart disease cancer mental illness asthma Often the hereditary component is polygenic o A trait that is controlled by two or more genes SexLinked Disorders in Humans A number of human conditions result from sexlinked x linked genes Redgreen color blindness is one example 0 It is characterized by a malfunction of lightsensitive cells in the eyes Hemophilia is a disease in which the blood does not clot properly
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