Unit 3 Cells need to possess the genetic material characteristic of the organism o Genetic material is DNA o The daughter cells need the complete genetic complement Prokaryotes Eukaryotes o Circular strands of DNA o Replicate the DNA and pass it onto the daughter cells o Divide by binary fission o A problem o Genetic material is found in linear chromosomes Linear strands of DNA complexed with proteins Multiple chromosomes humans have 46 Cell division Mitosis o Reproduction o Growth o Repair o Produce daughter cells that have identical genetic complements o Occurs in somatic cells Somatic cells Chromosomes o All body cells except cells which give rise to gametes o A complex of a linear strand of DNA and protein o Each eukaryotic species has a characteristic number of chromosomes o Found in the nucleus Duplicated chromosome o Consists of two sister chromatids o Identical copies of DNA o Attached at a specialized region called the centromere Interphase o Generally 90 of the cell cycle o Gap 1 G1 o S phase o Gap 2 G2 Gap 1 S phase o Synthesis of cell components o Increase in number of organelles o Synthesis replication of DNA o Doubling of the genetic material Gap 2 Centrioles o Centrioles replicate in animal cells o In animals o 9 sets of triplet microtubules arranged in a ring o Found in the centrosome A region from which microtubules grow out o Help organize microtubule growth But centrioles are not necessary DNA is replicated o S phase Mitosis o Prophase o Prometaphase o Metaphase o Anaphase o Telophase Prophase o Nucleoli disappear centromeres move away fro each other o Chromatin condenses o Mitotic spindle forms from microtubules in cytoplasm Prometaphase o Nuclear envelope fragments o Microtubules of spindle invade the nuclear region and interact with the chromosome via kinetochore Kinetochore o Structure of protein and specific sections of chromosomes DNA at the centromere Mitotic Spindle o Point of attachment from microtubules of the spindle o Forms from microtubules extending from the two centrosomes o As centrosomes move away from each other the microtubules get longer Metaphase Anaphase Telophase Cytokinesis cell wall o Centrosomes at opposite poles o Chromosomes arranges at the mid plane of the spindle o Sister chromosomes separate and move toward the poles o Nuclear envelope returns o Spindle breaks down o Nucleoli returns o Chromatids become less densely wiled o Diffusion of cytoplasm btw the 2 daughter cells o Mechanism differs btw plant and animal cells because plants have a Animals cell Plants o Actin microfilaments form a ring around the equator of the dividing o Interacting with myosin the actin ring tightens forming the cleavage furrow pinching off the two daughter cells o Vesicles from Golgi apparatus form a cell plate at the equator of the dividing cell o Checkpoint o GO phase o Form a new cell wall dividing the daughter cells Control systems for the cell cycle Stop and go ahead signals regulate the cycle Non dividing phase Most cells in the human body are non dividing Loss of Control of the cell cycle o Cancer Cells Continue dividing in the absence of growth signals Lack density dependent inhibition Lack anchory dependence Cell diffusion for gamete formation o Sexual reproduction Fusion of gametes from parents to form a zygote Greater diversity of offspring than asexual reproduction Must preserve the genetic complement characteristics of the species Must maintain the same number of chromosomes Chromosome complement o Each somatic cell has a characteristic of chromosomes Diploid chromosomes 2N Contains 2 of the basic sets Haploid chromosomes 1N Basic set of chromosomes o Karyotype Visualization of the complete set of chromosomes Best viewed at metaphase Sex chromosomes o Involved in determining sex o x y Autosomal chromosomes o All of the chromosomes o 46 23 pairs o 2 are sex 44 are autosomal Mitosis o To produce daughter cells with 2n chromosomes Meiosis o Cell diffusion for gamete production o In specialized tissues o Produces cells with 1N chromosomes o Two diffusions Meiosis 1 separates homologous chromosomes Meiosis 2 separates sister chromatid Asexual reproduction o Mitotic diffusion o Identical offspring Sexual reproduction Meiosis o Fuse gametes from parents to produce a zygote o Each parent contributes half of the genetic material o Increase the diversity of offspring DIFFERENT COMBINATIONS OF CHROMOSOMES o Increase the potential types of offspring o Occurs in cells that give rise to gametes o Produce cells with haploid 1n chromosome number o Mitosis occurs in somatic cells and produces diploid 2n daughter o Chromosome pairs align on equator of spindle o Kinetochores of sister chromatids are attached to fibers going to the cells Metaphase 1 same pole Anaphase 1 Telophase 1 o Homologous chromosome pairs separate o Sister chromatids remain together o Depending on the species o Nuclear membrane may reform o Cytokinesis may occur Meiosis 2 complement o Sister chromatids are separated Gamete formation in human males o Cell division like mitosis but starting with the haploid chromosome o Spermatogenesis in diploid reproductive tissues o Spermatocytes 2n undergo meiotic divisions and produce spermatids o Spermatids mature into spermatozoa Gamete formation in human females o Before birth o Oogonia 2n give rise to primary oocytes 2n stopped in prophase 1 o At ovulation meiosis continues with polar body 1n formation and a large egg 1n o Inheritance of mitochondria from the mother o Discrete unit of hereditary information consisting of a specific sequence of DNA o Often codes for a polypeptide chain o A particular position along a specific chromosome where a given gene Gene Gen Iocus is located Allele Homozygous o Alternative form of a gene o Having 2 identical alleles for a trait Example AA aa Example Aa bB Heterozygous o Having 2 different alleles for a trait Genotype Phenotype o The genetic makeup of an individual o The physical manifestation of a trait How it appears o Determined by the genotype Dominant allele o Allele that is fully expressed in the phenotype of a heterozygote o Only a single copy is required to express that trait o Represented by a capital letter A Recessive allele o In a heterozygous individual the allele that is completely masked not expressed in the phenotype o Represented by lower case letter a Why is it not expressed o Inactive or defective enzyme Generations o P o F1 Parental generation Filial one Offspring from the parental
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