MLS 2A - Cytogenetics Prelims PDF

BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino UNIT 1: HUMAN GENOME AND CELL GENE I. HUMAN GENOME o Units of heredity o Ap...

BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino UNIT 1: HUMAN GENOME AND CELL GENE I. HUMAN GENOME o Units of heredity o Application of Genetics/Genome II. CELL THEORY CHROMOSOMES o Cellular Functions o Threadlike structure mode of o Cell Parts and Function protein o Chemical Constituents o Serves to carry the genomic o Prokaryotic Cell o Eukaryotic Cell information from cell to cell o Organelles o Stem Cells III. CELL DIVISION AND DEATH NUCLEUS o Cell Cycle o Mitosis o Where most of cell’s DNA is o Control of the Cell Cycle stored o Meiosis CELL o Sperm form o Oocytes form o Basic unit of life o Meiosis and Mutations GENOME o Prenatal Development o The complete set of genetic instructions characteristics pf an organism including: I. HUMAN GENOME  Protein GENETICS  Encoding genes and other o Branch of biology concerned with DNA sequence heredity & genetic variation of GENOMIC how certain qualities or traits are o Large scale study of groups of passed from parents genes HEREDITY o Reveal how closely related we o Transmission of traits or are to each other and other characters and biological species. information between generation  Characters: hair color, eye Atom molecule cell organs organ color system organism human population  Traits: red hair, blue eyes VARIATION APPLICATION OF GENETICS/ GENOME o Differences that make an TAXONOMY organism unique from his parents o Naming DNA o Involved in the identification of o Transmits information in previously unknown sequence microorganism o Resembles a spiral staircase of AGRICULTURE o double helix (5’ and 3’) o Improvement of crop plants and o The rails or backbone is made of domestic animals sugar & phosphate MEDICINE  Sugar DNA is a 2- deocyribose (pentose) o Detection of heredity and non- heredity disease  The sugar is joined together by phosphate o Production of antibiotics group EVOLUTION  NITROGENOUS BASES: o Process by which living organisms change overtime  A-T through changes in the genome  G-C o Results from mutations that  Adenine and produce genomic variation Guanine – purines  Cytosine and II. CELL THEORY Thymine –  smallest unit that is capable of pyrimidines performing life functions BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino  Basic unit of life o Cells takes in the fluids along  All living things are made up of cell with dissolved small particles  All cells come from pre-existing cells EXOCYTOSIS through cell division. o Cell transport molecules out of the cell CELLULAR FUNCTIONS o Form of active transport CELL MEMBRANE o Requires the use of energy o Semi-permeable CELL PARTS AND FUNCTIONS o Allows only certain substance to pass through  Most cells are somatic cell (body cells) DIFFUSION and are said to have two (2) copies of o Movement of molecules from a genome (diploid). region of high to a region of low  Germ cell (gametes) which are sperm  Liquid; gas and egg cells, have one copy of the OSMOSIS genome and are haploid. o Diffusion of water across semi-  Stem cells are diploid cells that divide to permeable membrane from a give rise to differentiated cells and weak to strong solution replicate themselves in a process called ISOTONIC (no changes in self-renewal. RBC) o They enable the body to develop,  Water entering RBC grow, and repair damage. = water leaving CHEMICAL CONSTITUENTS RBC HYPERTONIC (RBC CARBOHHYDRATES shrink) o Provide energy and contributes to  RBC are dilute cell structure compared to LIPIDS external solution o Forms basis of some hormones, and lose water membrane, provide insulation, HYPOTONIC (RBC will stores energy swell and burst) PROTEIN  RBC take up too o Enables blood clotting much water o Forms bulk of connective tissues ACTIVE TRANSPORT ENZYME o Movement of area from high – o Catalyze biochemical reactions to low sustain life o Requires the use of ATP NUCLEIC ACIDS ATP – molecule that o Translate information from past supplies energy generations into specific proteins FACILITATED DIFFUSION that give a cell its characteristic. o Passive movement of molecules PROKARYOTIC CELL along the concentration of gradient  Simplest form of life ENDOCYTOSIS  No nucleus o Cells takes in substances from  Do not have structures surrounded by outside by engulfing them membrane PHAGOCYTOSIS  Few internal structures o Cells uses its plasma membrane  Unicellular to engulf a large particle, giving Bacteria rise to an internal compartment o CHARACTERISTIC OF called PHAGOSOME PROKARYOTIC CELL PINOCYTOSIS  They lack of nuclear membrane, mitochondria, BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino Golgi bodies, chloroplast, o COMPONENTS OF and lysosomes EUKARAYOTIC CELL (plant)  The genetic material is  Nucleus present in on a single  Mitochondria chromosome  Cell membrane  The histone protein, the  Chloroplast important constituents of  Cytoplasm eukaryotic chromosomes  Cell wall are lacking in them  Ribosome  The cell wall is made up of  Lysosome carbohydrates and amino  Golgi bodies acids.  Vacuole o STRUCTURAL FEATURES OF  Endoplasmic reticulum PROKARYOTIC CELL  Capsule ORGANELLES  Cell wall CYTOPLASM  Cytoplasm o Lies between the cell membrane  Cell membrane and nucleus  Pili o Contains the organelles  Flagella Functions  Ribosomes  House various  Plasmids organelles  Nucleic region  Acts as a medium from o COMPONENTS OF chemical reaction to PROKARYOTIC CELL take place  Plasma membrane  Support and protect  Cytoplasm cellular structures  DNA  Help transport  Ribosomes materials within the cell o REPRODUCTION IN CYTASOL PROKARYOTES  Asexually by binary fission  Gelatin like aqueous  Sexually by conjugation fluid that contains salt, minerals, and organic EUKARYOTIC CELL molecules MITOCHONDRIA  Most complex form of life o Sites of chemical reactions that  Have nucleus transfer energy from organic  Contained organelles surrounded by compounds to ATP membrane o “The power house of the cell”  Multicellular organisms o Have their own DNA  Most living organism o Have 2 membrane Animals and plants Smooth outer membrane o STRUCTURE OF EUKARYOTIC serves as a boundary CELL (plant) between the mitochondria  CELL WALL and the cytosol  Thick, rigid Inner membrane has membrane that many fold called cristae – surrounds the cell. they enlarged the surface This layer of area for more chemical cellulose fiber gives reactions the cell of its o Cells with high energy supports and requirements have more structure mitochondria BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino  Muscles & liver cells metabolism of Functions carbohydrates.  Produce the energy ROUGH ER – prominent necessary for the cell’s in cells that make large survival and functioning. amounts of proteins to be Through a series of exorted from the cell; chemical reactions, Ribosomes attached; mitochondria break Responsible for the down glucose into an synthesis of essential energy molecule lipids. known as ATP, which is GOLGI APPARATUS used to fuel various o Processing, packaging and other cellular secreting organelle processes. o System of membranes RIBOSOMES o Series of flattened sacs with o Most numerous convex shape o Not surrounded by a membrane o Works with the ER to modify o Made up of proteins and RNA proteins RNA is packaged into the o Consists of a series of flattened, ribosomes then membrane-bound sacs called transported to the cytosol cisternae o Some ribosomes are free, some Functions are attached to the ER  Manufacturer and Free ribosomes – protein shipping center of a to be used in the cytosol eukaryotic cell Ribosomes in the ER –  Responsible for proteins to be exported or manufacturing, inserted in the cell warehousing, and membrane shipping certain cellular Functions products (protein  Help in producing new glycoproteins, lipids, proteins by the enzymes) from the ER translational process  Modifies proteins and that involves three lipids, involves in the stages: initiation, formation of vesicles elongation, termination. and lysosomes, and They form amino acid secretions. chains at the rate of LYSOSOMES 200 amino acid er o Small spherical organelles minute o Enclose hydrolytic enzymes ENDOPLASMIS RETICULUM within single membrane o System of membranous tubules o Digest protein carbohydrates, and sacs lipids, DNA and RNA, old o INTRACELLULAR HIGHWAY – organelles, bacteria, viruses. molecules move from one part of o Rare in plants the cell to another. CYTOSKELETON o 2 types: o Maintains the shape and size of SMOOTH ER – cell responsible for synthesis o Network of long protein strands of essential lipids such as o Not surrounded by a membrane phospholipid and o Participates in the movement of cholesterol; production organelles and secretion of steroid MICROFILAMENTS – hormones; for the threads made of actin BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino (protein) – smallest o Site where ribosomes are strands synthesized MICROTUBULES – Function largest strands that are  Serve both as the hollow tubes. Help the repository of genetic cell divide by forming information and as the spindle fibers that cell’s control center. extend across the cell. CENTRIOLES  Function o Paired barrel-shaped organelles o Serves as highway located in the cytoplasm of for intracellular animal cells near the nuclear transport and envelope signaling o Play a role in organizing o Involved in cell microtubules that serves as the division processes, cell’s skeletal system and help and cilia and determine the locations of the flagella formation nucleus and other organelles o Involved in cell within the cell motility and o Involved in mitosis and meiosis migration cell division processes. o Provides structural PEROXISOMES support and help o Small vesicles, single membrane- maintain the shape bound organelles found in the of the cell. eukaryotic cells CILIA AND FLAGELLA o Contain digestive enzymes for o Hairlike organelles that extend breaking down the toxic materials from the surface of the cell in the cell and oxidative enzymes o Assist in movement for metabolic activity. CILIA – short and present CELL WALL in large membranes o Most commonly found in the plant FLAGELLA – long and cells & bacteria less numerous o Supports & protects cell NUCLEUS CHLOROPLAST o Most prominent structure o Usually found in plant cell o Maintain its shape with a protein o Contains green chlorophyl skeleton called nuclear matrix o Where photosynthesis takes o Double membrane – nuclear place envelope MICROVILI o Inside the envelope – chromatin o Small, finger-like projections that (DNA & protein) extends from the surface of When the cell is about to certain cells. Primarily in cells of divide it forms the epithelial tissues chromosomes Function o Stores hereditary information in  Increases surface area the DNA of the cells which o RNA is copied from the DNA enhances their RNA travels from nucleus capacity to absorb and to the cytosol through secrete nutrients, ions, small holes in the and other substances envelope – nuclear pores  Covered by plasma o Contains the nucleolus membrane that NUCLEOLUS contains transport o Inside the nucleus protein that facilitates o Contains RNA to build proteins BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino the movement of molecules into the cells o TOTIPOTENT STEM CELL  Can also have sensory  Formed shortly after functions in certain fertilization of an egg cell specialized cells by a sperm cell.  Can become all of the PLASMA MEMBRANE cells od the human body, o Outside the cell membrane as well as the cells of the Functions embryo and developing  Protecting the integrity fetus of the interior cell o PLURIPOTENT STEM CELLS  Providing support and  Give rise to all of the cell maintaining the shape types that form the human of the cell body (except placenta)  Helps in regulating cell  Can give rise to nearly all growth through the of the tissues that form the balance of endocytosis human body and exocytosis. o MULTIPOTENT STEM CELLS  More limited in what they can become  The cell types usually prefer to become cells of a certain class or category. NOTES: Animals are all multicellular, meaning multiple cells work together to form the whole organism In complex organisms, such as humans, these cells can be highly specialized to perform different functions. As such, they often looking and function very differently from one another, even though they are all human cells all cells are surrounded by a barrier called cell membrane they contain the molecule that carries STEM CELLS biological information – DNA  Stem cells and progenitor cells renew tissues so other cells are produced that III. CELL DIVISION AND DEATH take their places. As stem cell divided by  In a human body, new cells from old mitosis to yield either 2 daughter stem ones die, at different rates in different cells like itself, or one stem cell and one tissues. progenitor cell.  Growth, development, maintaining  Stem cell provide raw material for health, and healing from disease or producing specialized cells, while injury require an intricate interplay retaining the ability to generate new between the rate of mitosis and cells cytokinesis which divide the DNA and  Self-renewal is what makes a stem cell the rest if the cell, respectively, and a stem cell. apoptosis, a form of cell death.  Progenitor cell CANNOT self-renew, and  Apoptosis is a Greek word for “leaves its daughter cells specialize as any of falling from a tree”. It is a precise and restricted number or cell types. genetically programmed sequence if BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino events that is a normal part of o The period of cell cycle that development. varies the most duration among different cell types. THE CELL CYCLE S PHASE  Series of events that describes the o The cell replicates its entire sequence of activities as a cell prepares genome. This happens for and undergoes division. simultaneously from several  Rate varies in different tissues at starting points, to get the different times. A cell lining the small enormous job done. intestine’s inner wall may divide Centromere – are where frequently, throughout life, whereas a chromosome consists of neuron in the brain may never divide. two copies of the genome  Continual, but we describe it with stages. joined after DNA o Interphase replication. o Mitosis o Takes 8 to 10 hours. o Meiosis o Many proteins are also synthesized in this phase including: Spindle fibers – pull the chromosomes apart. Microtubules – form centrioles near the nucleus. o Centrosome – paired oblong structure where centriole microtubules join with other proteins and are oriented at right Cell numbers increase from mitosis and angles to each. decrease from apoptosis. G2 PHASE INTERPHASE o Occurs after the DNA has been o The cell continues the basic replicated but before mitosis biochemical functions of life, begins. while also replicating its DNA and Membranes are some organelles. assembled from molecules o Divided into: made during G1 and are G1 and G2 phases stored as small, empty S phase vesicles beneath the o The cell can exit the cell cycle at plasma membrane. These G1 to enter quiet phase called G0. vesicles will merge with the plasma membrane to G0 make enough of a o cell in G0 is not alive and boundary to enclose the maintains its specialized two daughter cells. characteristics but does not replicate its DNA or divide. o A cell may also proceed to mitosis and divide or die. G1 PHASE o The cell resumes synthesis of proteins, lipids, and carbohydrates. These molecules will contribute to building the extra plasma membrane required to surround the two new cells that form from the original one. BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino o The long strands of chromosomal material in replicated chromosomes. o If attached at a centromere, they are called sister chromatids.  The space between sister chromatids is called a furrow. PROPHASE o First stage of mitosis, DNA coils tightly. o Microtubules assemble from tubulin building blocks in the cytoplasm, forming the spindles. o Toward the end of prophase, the nuclear membrane breaks down and the nucleolus is no longer visible. METAPHASE o Chromosomes attached the spindle at their centromeres and align along the center of the cell. o The chromosome in this phase is under a great tension, but they appear motionless because they are pulled with equal force on both sides. ANAPHASE o Plasma membrane indents at the center. o A band of microfilaments forms on the inside face of the plasma membrane, constricting the cell down the middle. o The centromeres’ part, which relieves the tension and releases one chromatid from each pair to move to opposite ends of the cell breaking in the middle and the participants falling into two MITOSIS groups. Microtubule movements stretch the dividing cell.  Begins as the replicated chromosomes condensed enough to be visible, when TELOPHASE stained, under a microscope. o The cell looks like a dumbbell  The process by which a cell replicates with a set of chromosomes at its chromosomes and then segregates each end. them, producing two identical nuclei in o The spindle falls apart, and preparation for cell division. nucleoli and the membranes  Generally followed by equal division of around the nuclei re-form at each the cell’s content into two daughter cells end of the elongated cell. that have identical genome. CYTOKINESIS o Organelles and macromolecules CHROMATIDS are distributed between the two daughter cells. BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino o The microfilament band contracts that mitosis rather than apoptosis like a drawstring, separating the occurs. newly formed cells. Spindle assembly checkpoint o Overseas construction of the spindle and the binding of chromosomes to it.  Cells obey an internal “clock” that tells them approximately how many times to divide. Mammalian cells that grow in a dish are divided about 40-60 times. Telomeres o Function like cellular fuses that burn down as pieces are lost from the ends. o Consist of hundreds to thousands or repeats of a specific six DNA- base sequence. o Lose 50-200 endmost bases, gradually shortening the chromosomes at each mitosis. o The rate of telomere shortening provided a cellular “clock.”  Chronic stress, obesity, lack of exercise, and elevated blood sugar are associated with accelerated telomere shortening. CONTROL OF THE CELL CYCLE  Factors from outside the  Control of mitosis is a daunting task. cell ca affect a cell’s  Quadrillions of mitoses occur in a mitotic clock. Crowding lifetime, and not at random. can slow or halt mitosis.  Too little mitosis and an injury goes  Not all cells have unrepaired, too much and an abnormal shortening telomeres. In growth form. eggs and sperm, in cancer cells, and in a few types of Checkpoints normal cell that must o Groups of interacting proteins continually supply new function at specific times in the cells, an enzyme called cell cycle. telomerase keeps o Ensure that chromosomes are chromosome tips long. correctly replicated and apportioned into daughter cells. DNA checkpoint o Temporarily pauses the cell cycle while special proteins repair damaged DNA. Apoptosis checkpoint o Turns on as mitosis begins. o Proteins called survivins override signals telling the cell to die, so BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino  Explains why siblings differ genetically from each other and from their parents. MEIOSIS I o Reduces the number of replicated chromosomes from 46 to 23. MEIOSIS II o Produces four cells from the two cells formed in the first division by splitting the replicated HORMONE chromosomes. o Made in gland and transported in  The colors represent the contributions of the bloodstream to another part the two parents, whereas sizes of the body, where it exerts a distinguish different chromosomes. Only specific effect. two types of chromosomes are depicted CYCLINS AND KINASES due to space constraints. In the body there would be 23 pairs of replicated o Interact inside cells, activating the genes whose products carry out chromosomes as meiosis begins. mitosis. o Cyclins’ levels fluctuate regularly, GAMETES while kinase’ level stays the same. o Contribute 23 different o A certain number of cyclin-kinase chromosomes, constituting one pairs turn on the genes that copy of the genome to fertilized trigger mitosis. ovum. APOPTOSIS o Haploid, which means that they o Rapidly and neatly dismantles a have only one of each type of cell into membrane-closed pieces chromosomes. that a phagocyte can mop up. o In contrast, somatic cells contain 23 pairs of chromosomes or 46 in o Like packing the contents of a total. messy room into garbage bags, then disposing of it all.  One member of each pair o A form of cell death associated comes from the person’s with inflammation and damage, mother, and one comes rather than an orderly, contained from the father. destructions. HOMOLOGOUS PAIRS o Begins when a “death receptor” o Have the same genes in the on the cell’s plasma membrane same order but may carry receives a signal to die. different alleles, or variants, of the same gene. MEIOSIS  Type of cell division that form gametes from a special cell called germline cells, that halves the chromosomes number.  Further process, maturation, sculpts the distinctive characteristics of a sperm and oocyte.  Without meiosis, the sperm and oocyte would each contain 46 chromosomes, and the fertilized ovum would have twice the normal number of chromosomes, or 92. BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino PROPHASE I o The replicated chromosomes condense and become visible when stained. o Spindle fibers forms towards the middle. o The homolog lines up next to one another, gene by gene, in an event called synapsis. o A mixture of RNA and protein holds the chromosome pairs together. o Towards the end of prophase 1, the synapsed chromosomes separate but remain attached at a few points along their lengths. METAPHASE II o The homologous align down the center of the cell. o Each member of the homologous pair attaches to a spindle fiber at an opposite pole. o For each homologous pair, the pole maternally or paternally derived member goes to is random. o 23 boys and 23 girls can line up in opposite-sex pairs. ANAPHASE I and TELOPHASE I o Homologs separate in anaphase 1. o Homologs move to opposite poles in telophase 1. BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino PROPHASE II marrow speed through G1 in 16 to 24 o the start of the second meiotic hours. division.  Cells of the embryo may skip G1 entirely. o The chromosomes are again condensed and visible. METAPHASE II SPERM FORM o The replicated chromosomes align down the center of the cell. Spermatogenesis ANAPHASE II o The formation of sperm cells o The centromeres’ part, and newly begins in a diploid stem cell formed chromosomes, each now called a spermatogonium. unreplicated form, move to Spermatogonium opposite poles. o divides mitotically, yielding two TELOPHASE II daughter cells. One cell o Nuclear envelopes form around continues to specialize into a the four nuclei, which then mature sperm. The other separate into individual cells. daughter cells remain a stem cell, able to self-renew and continually produce more sperm. o Bridges of cytoplasm attach several spermatogonia, and their daughter cells enter meiosis together. As these spermatogonia mature, they accumulate cytoplasm and replicate their DNA, becoming primary spermatocytes.  During meiosis I, each primary spermatocyte Notes: divides, forming two equal-  the centromeres of each homolog in sized haploid cells called meiosis 1 remain together. secondary spermatocytes.  The result of meiosis is four haploid  In meiosis II, each cells, each carrying a new assortment of secondary spermatocyte genes and chromosomes that hold a single copy of genome. divides to yield two equal-  Meiosis generates astounding genetic sized spermatids. variety.  Each spermatid then  SYNAPSIS develops the characteristic o Homologs exchange parts or flagellum. After spermatid cross over. differentiation, some of the o All four chromatids that comprise cytoplasm connecting the each homologous pair align as exchanges occur. cells falls away, leaving o After crossing over, each mature, tadpole-shaped homolog bears some genes from spermatozoa. each parent.  The greater the number of chromosomes, the greater the genetic diversity generated in metaphase 1. For two pairs of homologs, four different metaphase alignments are possible. For three pairs of homologs, eight different alignments can occur.  Slowly dividing cells, such as those in the liver may exit at G1 and enter G0 where they remain for years.  The rapidly dividing cells in bone BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino and the cell becomes a primary oocyte.  Primary oocyte divides into two cells: o First polar body – small cell with very little cytoplasm and may decompose. o Secondary oocyte – much Acrosome larger cell that divided unequally o Contains enzymes that help the in meiosis II to produce another sperm cell penetrate the small polar body with protective layers around the unreplicated chromosomes and oocyte. the mature egg cell, or ovum. o Within the large sperm head, DNA is wrapped around proteins.  Rarely, sperm fertilizes a polar body. When this happens, the woman’s hormones respond as if she is pregnant, but a disorganized clump of cells that is not an embryo grows for a few weeks and then leaves the woman’s body.  Before birth, a female has a million or so oocytes arrested in prophase I.  By puberty, about 400,000 oocytes remain.  After puberty, meiosis I continues in one Notes: or several oocytes each month, but halts  Meiosis in the male has built-in protections that help prevent sperm from again at metaphase II. causing some birth defects. o Ovulation – response to a  Spermatogonia that are exposed to specific hormonal cues each toxins tend to be so damaged that they month. One ovary release never mature in sperm. secondary oocyte.  The oocyte drops into a uterine tube, OOCYTES FORM where waving cilia moves it toward the uterus. Along the way, if a sperm Oogenesis penetrates the oocyte membrane, o Meiosis in the females begins female meiosis completes and a with diploid cell called oogonium. fertilized ovum form. Oogonia/oogonium  If the secondary oocyte is not fertilized, o Not attached to each other. it degenerates and leaves the body in Instead, follicle cells surround the menstrual flow, without meiosis them. completed. o As they grow, cytoplasm  Only one in three of the oocytes that do accumulates, DNA replicates, meet and merge with a sperm cell will BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino continue to grow, divide, and specialized Sperm and Oocyte meet at to eventually form a new individual. fertilization. o Sperm cells can survive in a woman’s body for up to 3 days, but the oocyte can only be fertilized in the 12 to 24 hours after ovulation. o The woman’s body helps sperm reach an oocyte.  Capacitation – a process in female that chemically activates sperm, and the MEIOSIS AND MUTATIONS oocyte secretes a chemical that attracts  The gametes of older people are more sperm. likely to have new mutations than the o Fertilization begins when the gametes of younger people. outer membranes of the sperm  Older women are at higher risk of and secondary oocyte meet and producing oocytes that have an extra or a protein on the sperm head missing chromosomes. contacts a different type of  Older men are also more likely to protein in the oocyte. produce gametes that have genetic o Fertilization is complete when the errors. two genetic packages meet and merge, forming the genetic Paternal age effect instructions for a new individual. o Causes dominant single-gene  Zygote – the fertilized diseases. That is, only one copy ovum. of the mutant gene causes the condition. o Conditions arise from stem cells in the tests is that divides every 16 days, from puberty on, offering many opportunities for DNA replication to make a mistake, generating a dominant mutation, o They occur in genes of the fibroblast growth factor receptor family and affect skeletal growth. PRENATAL DEVELOPMENT Embryo o A prenatal human The Embryo Cleaves and Implants o The first 8 weeks, when o A day after fertilization, the rudiments of all body parts form. zygote divides by mitosis. o “preimplantation” stage  Cleavage – a period of o Not yet settled into the uterine frequent cell division. lining.  Blastomeres – the Fetal period resulting early cells o Structures grow and specialize/  Morula – the embryo Fetus when the blastomeres o From the start of ninth week until form a solid ball of sixteen birth. or more cells. o Prenatal human organisms o During the cleavage, organelles and molecules from the BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino secondary oocyte’s cytoplasm o The placenta is fully developed by still control cellular activities, but 10 weeks. The placenta is an organ some of the embryo’s genes that, for the duration of pregnancy, begin to function. connects the woman and fetus. o The developing embryo is nurtured o The ball of cells hollows out, and by other structures. The allantois, a its center fills with fluid, creating a membrane surrounding the embryo blastocyst. Some the cells form a that develops into the umbilical clump on the inside lining called blood vessels, as well as the yolk inner cell mass. sac both produce blood cells. o A week after conception, the blastocyst nestles into the uterine lining. THE EMBRYO DEVELOPS o Embryonic induction – specialization of one group of cells THE EMBRYO FORMS causes adjacent groups of cells to o The amniotic cavity develops specialize. between the inner cell mass and the o Organogenesis – the outer cells anchored to the uterine transformation of the simple three lining during the second week of layers of the embryo into distinct prenatal development. organs.  Ectoderm – 1st layer. o Neural tube – develops into the Closest to the amniotic brain and spinal cord. cavity o NTD – neutral tube defect  Mesoderm – 2nd layer. o AFP – alpha fetoprotein Located nearest to the o Lack of the B vitamin folic acid can cause NTD. blastocyst cavity. o Third week – prenatal develop a  Endoderm – 3rd layer. band called the primitive streak Forms the middle. appears along the back of the embryo. o Fourth week – the embryonic existence is one of spectacularly rapid growth and differentiation. o Fifth & sixth week – the embryo’s head appears too large for the rest of its body. o Seventh & eighth week – a skeleton composed of cartilage SUPPORTIVE STRUCTURE FORMS forms. o By the third week after conception, chorionic villi—finger-like growths that project into pools of the woman's blood—extend from the part of the embryonic disc close to the uterine wall. BS MEDICAL LABORATORY SCIENCES MLS 2A − CYTOGENETICS 1st Semester ⃒ Ms. Yvonne Capatayan ⃒ University of San Agustin ⃒ Nika Onekin Balino THE FETUS GROWS o Sex is determined at conception, when a sperm bearing an X or Y chromosome meets an oocyte, which always carries an X chromosome. o By week 12, the fetus sucks its thumb, kicks, makes fists, and faces, and has the beginnings of teeth. o By the fourth month, the fetus has hair, eyebrows, lashes, nipples, and nails. o By 18 weeks, the vocal cords have formed. o By the end of the fifth month, the fetus curls into a head-to-knees position. o The sixth month, the skin appears wrinkled. o The final trimester, fetal brain cells rapidly link into networks as organs elaborate and grow. o Some birth defects are caused by a mutation. o rare inherited condition called phocomelia. o Many birth defects are caused by toxic substances. o Chemicals or other agents that cause birth defects are called teratogens (Greek for “monster- causing”). o Most drugs are not teratogens.