Biology 111: Ch 10, 11, 12, 13
Biology 111: Ch 10, 11, 12, 13 BIOL 111
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This 37 page Bundle was uploaded by Megan Giesler on Wednesday March 2, 2016. The Bundle belongs to BIOL 111 at University of North Dakota taught by Christopher Felege in Spring 2016. Since its upload, it has received 104 views. For similar materials see Concepts of Biology in Biological Sciences at University of North Dakota.
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Biology 111: Concepts of Biology Chapter 10 10.1Mendel’s Laws Gregor Mendel was an Austrian monk who worked with garden pea plants in 1860s. When he began his work, most acknowledged that both sexes contributed equally to a new individual. Unable to account for presence of variations among members of a family over generations Mendel’s model is compatible with evolution o Various combinations of traits are tested by the environment. o Combinations that lead to reproductive success are the ones that are passed on with the greatest frequency. Mendel’s experimental procedure Used garden pea, Pisum sativa o Easy to cultivate, short generation time o Normally self-pollinates but can be cross-pollinated by hand Chose true-breeding varieties o Offspring were like the parent plants and each other Parent plants pass on the same genes; no crossing over Kept careful records of large number of experiments His understanding of mathematical laws of probability helped interpret results. Particulate theory of inheritance Based on the existence of minute particles (genes) Monohybrid cross o One-trait inheritance o Original parents called P generation First-generation offspring 1 generation Second-generation offspring F g2neration Punnett square o Shows all possible combinations of egg and sperm offspring may inherit When F 1llowed to self-pollinate, F2were 3/4 green and 1/4 yellow o F1had passed on yellow pods Mendel reasoned 3:1 ratio only possible if o F1parents contained 2 separate copies of each heritable factor 1 dominant and 1 recessive o Factors separated when gametes were formed and each gamete carried only 1 copy of each factor o Random fusion of all possible gametes occurred at fertilization One-trait testcross o To see if the1F carries a recessive factor, Mendel crossed 1is F generation green pod (dominant) plants with true-breeding, yellow pod plants (recessive). He reasoned that half the offspring would be green and half would be yellow. His hypothesis that factors segregate when gametes are formed was supported. o Testcross Used to determine whether or not an individual with the dominant trait has two dominant factors for a particular trait o If a parent with the dominant phenotype has only one dominant factor, the results among the offspring are 1:1. o If a parent with the dominant phenotype has two dominant factors, all offspring have the dominant phenotype. Mendel’s first law of inheritance: Law of segregation o Cornerstone of his particulate theory of inheritance The law of segregation states the following: o Each individual has two factors for each trait o The factors separate during the formation of the gametes o Each gamete contains only one factor from each pair of factors o Fertilization gives each new individual two factors for each trait The modern genetics view Scientists note parallels between Mendel’s particulate factors and chromosomes Chromosomal theory of inheritance o Chromosomes are carriers of genetic information o Traits are controlled by discrete genes that occur on homologous pairs of chromosomes at a gene locus. Each homologue holds one copy of each gene pair. o Meiosis explains Mendel’s law of segregation and why only one gene for each trait is in a gamete. When fertilization occurs, the resulting offspring again have two genes for each trait, one from each parent. Terminology Alleles o Alternative forms of a gene o Dominant allele masks the expression of the recessive allele For the most part, an individual’s traits are determined by the alleles inherited. Alleles occur on homologous chromosomes at a particular location called the gene locus. Genotype o Describes the alleles present in an individual o Homozygous or heterozygous, dominant or recessive o Ex: PP, Pp, pp Phenotype o Describes the physical appearance of that individual o Ex: Purple, white Genotype versus phenotype o Genotype Alleles individual receives at fertilization Homozygous: two identical alleles o Homozygous dominant (PP, GG, etc.) o Homozygous recessive (pp, gg, etc.) Heterozygous: two different alleles o Pp, Gg, etc. o Phenotype: physical appearance of individual Mostly determined by genotype Ex: PP & Pp = purple; pp = white Dihybrid crosses o Two-trait inheritance o Mendel crossed tall plants with green pods (TTGG) with short plants with yellow pods (ttgg). o F1plants showed both dominant characteristics Tall and green pods. o 2 possible results f2r F If the dominant factors always go into gametes togeth2r, F will have only 2 phenotypes. Tall plants with green pods Short plants with yellow pods If four factors segregate into gametes independently, 4 phenotypes would result TG TG TG TG TG Tg tG tg tg TtGg TtGg TtGg TtGg TG TTGG TTGg TtGG TtGg tg TtGg TtGg TtGg TtGg Tg TTGg TTgg TtGg Ttgg tg TtGg TtGg TtGg TtGg tG TtGG TtGg ttGG ttGg tg TtGg TtGg TtGg TtGg tg TtGg Ttgg ttGg ttgg Based on the results, Mendel formulated his second law of heredity. Law of independent assortment o Each pair of factors assorts independently of the other pairs. o All possible combinations of factors can occur in the gametes. When all possible sperm have an opportunity to fertilize all possible eggs, the expected phenotypic results of a two-trait cross are always 9:3:3:1. Two-trait testcross o Fruit fly Used in genetics research o Wild-type fly has long wings and gray body Some mutants have vestigial wings and ebony bodies L= long, l = short, G = gray, g = black o Can’t determine genotype of long-winged gray-bodied fly (L_G_) Second allele at each locus could be dominant or recessive Cross with short-winged black-bodied fly (llgg) Note that the homozygous recessive PHENOTYPE is the only GENOTYPE you can KNOW by just looking at it. Mendel’s laws and probability o Punnett square assumes Each gamete contains one allele for each trait Law of segregation Collectively the gametes have all possible combinations of alleles Law of independent assortment Male and female gametes combine at random o Use rules of probability to calculate expected phenotype ratios o Rule of multiplication Chance of two (or more) independent events occurring together is the product of their chances of occurring separately Coin flips: odd of getting tails is ½, odds of getting tails when you flip 2 coins ½ × ½ = ¼ Mendel’s laws and meiosis o Gene for earlobes and hairline on different chromosomes o Gametes have all possible combinations of alleles 10.2 Mendel’s Laws Apply to Humans Pedigree o Chart of a family’s history in regard to a particular genetic trait Males are squares Females are circles Shading represents individuals expressing disorder Horizontal line between circle and square is a union Vertical line down represents children of that union o Counselor may already know pattern of inheritance and then can predict chance that child born to a couple would have the abnormal phenotype Pedigrees for autosomal disorders o Autosomal recessive disorder Child can be affected when neither parent is affected Heterozygous parents are carriers. Parents can be tested before having children. Ex: People affected = aa People unaffected = AA, Aa o Aa = carrier Slide 41 o Autosomal dominant disorder Child can be unaffected even when parents are heterozygous and therefore affected When both parents are unaffected, none of their children will have the condition because there is no dominant gene to pass on. Ex: People affected = AA, Aa People unaffected = aa Genetic disorders of interest Autosomal disorders o Methemoglobinemia Lack enzyme to convert methemoglobin back to hemoglobin Relatively harmless, bluish-purplish skin o Cystic fibrosis Autosomal recessive disorder Most common lethal genetic disorder among Caucasians in U.S. Chloride ion channel defect causes abnormally thick mucus o Alkaptonuria Autosomal recessive disorder Lack functional homogentisate oxygenase gene Accumulation of homogentisic acid turns urine black when exposed to air o Sickle cell disease Autosomal recessive disorder Single base change in globin gene changes 1 amino acid in hemoglobin Makes red blood cells sickle-shaped Leads to poor circulation, anemia, low resistance to infection o Huntington disease Autosomal dominant disorder Progressive degeneration of neurons in brain Mutation for huntingtin protein Patients appear normal until middle-aged—usually after having children Test for presence of gene 10.3 Beyond Mendel’s Laws Incomplete dominance o Heterozygote has intermediate phenotype o Familial hypercholes-terolemia is an example in humans. Persons with one mutated allele have an abnormally high level of cholesterol in the blood, and those with two mutated alleles have a higher level still. o Human wavy hair is intermediate between curly and straight hair. o Pink is the intermediate between red and white flowers Multiple-allele traits o ABO blood group inheritance has 3 alleles I = A antigen on red blood cells B I = B antigen on red blood cells i = neither A nor B antigen on red blood cells o Each person has only 2 of the 3 alleles o Both I and I are dominant to i A B o I and I are codominant Both will be expressed equally in the heterozygote Polygenic inheritance o Trait is governed by 2 or more sets of alleles o Each dominant allele has a quantitative effect on phenotype and effects are additive o Result in continuous variation—bell-shaped curve o Multifactorial traits—polygenic traits subject to environmental effects Cleft lip, diabetes, schizophrenia, allergies, cancer, skin color, and height Due to combined action of many genes plus environmental influence Environmental influences Relative importance of each can vary o Temperature can effect coat color. Rabbits homozygous for ch have black fur where the skin temperature is low. Enzyme encoded by gene is active only at low temperatures Pleiotropy o Single genes have more than one effect. o Marfan syndrome is due to production of abnormal connective tissue Linkage 2 traits on same chromosome—gene linkage 2 traits on same chromosome do NOT separate independently More likely for a to separate from c than it is from b Recombination between linked genes o Linked alleles stay together Heterozygote forms only 2 types of gametes, produces offspring only with 2 phenotypes 10.4 Sex-Linked Inheritance Females are XX o All eggs contain an X Males are XY o Sperm contain either an X or a Y Y carries SRY gene o Determines maleness X is much larger and carries more genes o X-linked Gene on X chromosome Sex-linked alleles Fruit flies have same sex chromosome pattern as humans When red-eyed female mated white mutant white-eyed male, all offspring were red-eyed o In the 2 , the 3:1 ratio was found but all of the white-eyed flies were males Y chromosome does not carry alleles for X-linked traits this is why it is more likely for a male to have an x-linked disease because females need both X chromosome to be effected while males only need the one. Males always receive X from female parent, Y from male parent Carrier o Female who carries an X-linked trait but does not express it Pedigree for sex-linked disorder X-linked recessive disorder o Sons inherit trait from mothers o More males than females have disorder Allele on the one X chromosome is always expressed in males o Females who have the condition inherited the mutant allele from both their mother and their father o Conditions appear to pass from grandfather to grandson X-linked dominant o Only a few traits o Daughters of affected males have the condition o Affected females can pass condition to daughters and sons Depends on which X inherited from a carrier mother if father is normal Y chromosome o Not very common only a few disorders o Present only in males and are passed to all sons but not daughters X-linked recessive disorders o Color blindness About 8% of Caucasian men have red-green color blindness o Duchenne muscular dystrophy Absence of protein dystrophin causes wasting away of muscles Therapy Immature muscle cells injected into muscles Biology 111: Concepts of Biology Chapter 11 11.1 DNA and RNA Structure and Function Mendel knew nothing about DNA. It took years for investigators to conclude Mendel’s factors (genes) were on chromosomes. Controversy over whether DNA or protein was the genetic message o Experiment using viruses showed only DNA directed the formation of new viruses Alfred Hershey and Martha Chase determined that DNA is the genetic material. o Their experiment involved a virus that infects bacteria, such as E. coli. o They wanted to know which part of the virus entered the bacterium Capsid made of protein DNA inside the capsid o Radioactive tracers showed that DNA, not protein, enters the bacterium and guides the formation of new viruses. Therefore, DNA must be the genetic material. Structure of DNA Race to determine the structure Chargaff’s rules o Knew DNA contains 4 types of nucleotides o Examined DNA from many species The amount of A, T, G, and C in DNA varies from species to species. In each species, the amount of A = T and the amount of G = C. Nucleotides contain phosphate, a 5-carbon sugar, and nitrogen-containing base. *The only nucleotides that have 2 parts end in “nine” Franklin’s X-ray diffraction data Rosalind Franklin was studying the structure of DNA. Her data showed DNA to be a helix with some portions repeating over and over. The Watson and Crick model 1951: o James Watson and Francis Crick set out to bring together all the data on DNA and build a model o The model suggested how replication works. o Their model holds true today with few changes. o Won the Nobel Prize DNA structure DNA structure is a double helix, like a twisted ladder Deoxyribose sugar and phosphate molecules are bonded, forming the sides, with the bases making up the rungs of the ladder. Complementary base pairing of A&T and G&C Hydrogen bonding between the bases holds the halves of the helix together. Replication of DNA o Process of copying DNA before cell division o Two strands separate Each strand serves as a template for a new strand o Semiconservative Each new DNA molecule is made of one parent strand and one new strand o Replication requires Unwinding Helicase (enzyme) Complementary base pairing Joining DNA polymerase and DNA ligase o New DNA molecule exactly identical to original molecule Semiconservative replication o Parent strand unwinds and separates by actions of helicase o New strands form through complementary base pairing by actions of DNA polymerase. o DNA ligase seals any breaks in the sugar-phosphate backbone. o New DNA molecule will be half old and half new o New DNA molecule will be exactly identical to original molecule In eukaryotes o DNA replication begins at numerous origins of replication. Forms “replication bubbles” This allows space for the DNA to be replicated Bubbles spread in both directions until they meet. RNA structure and function Ribonucleic acid (RNA) Contains sugar ribose Uses uracil, not thymine o Uses A, C, and G like DNA Single-stranded 3 majors types o Messenger RNA (mRNA) o Transfer RNA (tRNA) o Ribosomal RNA (rRNA) Messenger RNA (mRNA) Produced in the nucleus from DNA template Carries genetic message to ribosomes Transfer RNA (tRNA) Produced in the nucleus from DNA template Transfers amino acids to ribosomes Each type carries only one type of amino acid Ribosomal RNA (rRNA) Produced in the nucleolus of the nucleus from DNA template Joins with proteins to form ribosomes Ribosomes may be free or in polyribosomes (clusters) or attached to ER 11.2 Gene Expression Early 1900s, Sir Archibald Garrod suggests a relationship between inheritance and metabolic diseases o First to suggest a link between genes and proteins DNA provides a blueprint to synthesize proteins. o Information flows from DNA to RNA to protein Transcription DNA serves as template to make mRNA Translation mRNA directs sequence of amino acids in a protein rRNA and tRNA assist The genetic code Translates from nucleic acids to amino acids Triplet o 3 nucleotide sequence in DNA Codon o 3 nucleotide sequence in mRNA A codon encodes a single amino acid. Start and stop codons Transcription During transcription, complementary RNA is made from a DNA template. Portion of DNA unwinds and unzips at the point of attachment of RNA polymerase Bases join in the order dictated by the sequence of bases in the template DNA strand. Newly made pre-mRNA must be processed. Capping and addition of poly-A tail provides stability Introns (non-coding) removed Leaves only exons (coding) Alternative splicing can produce different versions of mRNA leading to different proteins. Now mature mRNA leaves nucleus and associates with ribosome on cytoplasm Translation tRNA brings in amino acids o Anticodon Group of 3 bases complementary to a specific codon of mRNA After translation is complete, a protein contains the sequence of amino acids originally specified in the DNA. Ribosomes are composed of protein and rRNA. o Site of translation Protein synthesis o Binds mRNA and 2 tRNA molecules P site for a tRNA attached to a peptide A site for newly arrived tRNA with an amino acid 3 phases of translation o Initiation o Elongation o Termination Initiation mRNA binds to small subunit of ribosome Large subunit then joins Elongation o Peptide lengthens one amino acid at a time Termination o 1 of 3 stop codons reached o Release factor causes ribosomal subunits and mRNA to dissociate o Complete polypeptide (protein) released 11.3 Gene Regulation Levels of gene expression control Body contains many cells that differ in structure and function Only certain genes are active in cells that perform specialized functions Housekeeping genes govern functions common to all cells Activity of selected genes accounts for specialization Gene expression in prokaryotes Escherichia coli (E. coli) lives in our intestine and can quickly adjust its enzymes according to what we eat. If we drink milk, E. coli immediately begins to make 3 enzymes needed to metabolize lactose. Operon o Cluster of bacterial genes along with DNA control sequence François Jacob and Jacques Monod: Nobel Prize 1961 for lac operon Lactose not available most of the time (Image below) E.coli does not normally transcribe the genes of the lac operon. When lactose is not present, repressor binds to operator and RNA polymerase cannot attach to the promoter Inhibits transcription When lactose is present, it binds to the repressor. (Image below) o Repressor is inactivated and cannot attach to operator o RNA polymerase can bind and transcription occurs. System can also work for genes normally turned on o Binding of tryptophan (gene for synthesis normally on) causes operator to be turned off *The book has a good video to watch about lac operator. Felege stated that he would not test us on the lac operator but will ask us questions about repressors and promoters Gene expression in eukaryotes Each gene has its own promoter. Employ a variety of mechanisms o Affect whether gene is expressed, speed of expression, and length of expression Some mechanisms occur in nucleus and others in cytoplasm o Nucleus Chromatin condensation, mRNA transcription, and mRNA processing o Cytoplasm Delay of transcription, duration of mRNA or protein Chromatin condensation o Way to keep genes turned off o More tightly compacted = less gene expression o Heterochromatin Dark staining regions of tightly compacted, inactive chromatin o Barr body Second X chromosome in mammalian females is turned off http://www.bio.miami.edu/dana/dox/calico.html This is a good site that explains more on how Barr Body works. Euchromation o Unpacked heterochromatin o Contains active genes o Nucleosome Portion of DNA wrapped around histones o Transcription activator pushes aside histones so that transcription can begin. DNA transcription o Same principles as prokaryotic transcription but with more regulatory proteins per gene o Allows for greater control but also a greater chance for malfunction o Transcription factors DNA-binding proteins that help RNA polymerase bind to a promoter Several needed in each case, need all of them Form a complex that helps pull apart helix and helps position RNA polymerase Same ones used in different combinations If one is defective, it can have serious effects like Huntington disease Speed up transcription Bind to enhancer region of DNA Possible for a single transcription factor to have dramatic effect on gene expression MyoD alone can activate the genes necessary for fibroblasts to become muscle cells. Ey can bring about the formation of a complete eye in flies. mRNA processing o After transcription, introns must be removed and exons spliced together. o Alternative mRNA processing allows cells to produce multiple proteins from the same gene by changing the way exons are joined. o Fruit fly DScam gene can produce over 38,000 different combinations mRNA translation o Cytoplasm contains proteins that determine whether translation takes place o Environmental conditions can delay translation. Red blood cells do not produce hemoglobin unless heme is available. o The longer mRNA remains in the cytoplasm before it is broken down, the more gene product is produced. It can be affected by length of poly A tail or presence of hormones Protein activity o Some proteins are not active immediately after synthesis. Insulin must be processed before it is an active form. o Allows protein’s activity to be delayed until needed Signaling between cells in eukaryotes o In multicellular organisms, cells are constantly sending out chemical signals that influence the behavior of other cells. During development, signals determine what a cell becomes. Later, they help coordinate growth and daily functions. o Cell-signaling pathway Begins when chemical signal binds to receptor on target cell plasma membrane Initiates signal transduction pathway End product affects cell (not original signal itself) Biology 111: Concepts of Biology Chapter 12 12.1 Biotechnology Genetic engineering o Inserting cloned genes into an organism Transgenic organism Cloning genes o Making identical copies Because the genetic code is nearly universal, it’s possible to transfer cloned genes between virtually any organism. Recombinant DNA technology Recombinant DNA (rDNA) contains DNA from 2 or more different organisms. A vector is used to carry the foreign DNA. o May be a plasmid from bacteria Restriction enzymes are molecular scissors. o Cut DNA at specific sites o “Sticky ends” DNA ligase used to join pieces of DNA together Human insulin made by bacterial cells Human gene removed Inserted into plasmid Plasmid inserted into bacteria Bacteria produce insulin as if it was one of their own gene products. Polymerase chain reaction (PCR) Amplifies specific DNA sequences o DNA polymerase makes DNA From Thermus aquaticus which tolerates high temperatures o Primer is a specific DNA segment to be amplified Doesn’t amplify all DNA only the target o Cycles over and over again doubling amount of DNA at each cycle DNA fingerprinting Makes use of repeating noncoding DNA segments o People differ in how many repeats Can use PCR (Polymerase chain reaction) to increase amount of DNA sample Electrophoresis separates samples by size. o Longer DNA strands are larger and migrate less on the gel. 12.2 Stem Cells and Cloning Every cell in your body: Receives a copy of all genes o Think back to mitosis Has the potential to become a complete organism Cloning uses this potential o Reproductive cloning o Therapeutic cloning Reproductive cloning Desired end is an individual exactly like the original Plant cloning routine Cloning of adult animals was thought to be impossible March 1997: Dolly, cloned Dorset sheep o Adult nucleus placed in enucleated cell o Donor cells starved causing them to go into G0. o G 0uclei can be signaled to initiate development. Farm animals with desirable traits commonly cloned Some endangered animals cloned In U.S., no federal funds can be used for experiments to clone humans o Even cloning animals is inefficient and may not produce healthy animals Telomeres at the end of the DNA may be short, and the embryo is essentially born “old” Therapeutic cloning Desired end is mature cells for o Learning more about cell specialization o Use in treating human illnesses Can be carried out in several ways o Embryonic stem cells Common but ethical concerns Unlimited in the number of cells they can become o Adult stem cells Limited in number of cells they can become May be able to overcome limitation 12.3 Biotechnology Products Transgenic organisms Biotechnology o Use of natural biological systems to create a product Organisms can be genetically engineered for use in biotechnology. Transgenic bacteria o Grown in bioreactors o Gene product collected from growth medium Transgenic plants and animals o Cotton, corn, and potato make their own insecticide o Soybeans herbicide resistant o Larger fishes, cows, and pigs from inserted growth hormone gene o “Pharming” Use of transgenic farm animal to produce pharmaceuticals in milk o Transgenic animals may be cloned Nucleus from adult cell introduced into enucleated egg cell produces identical genotype of adult donor Genetically Modified Organism (GMO) o A GMO is an organism whose genetic material has been altered using genetic engineering techniques. GMO Crop Benefits o Bigger yields to create more efficient use of land o Less uses of herbicides and other pesticides. o More drought and disease resistant/tolerant o Foods with better texture, flavor and nutritional value. o Foods with a longer shelf life for easier shipping. o With an ever increasing global population, world hunger, and an epidemic of mal/undernourished people, there is a potential promise in the use of this technology to benefit societies worldwide. GMO concerns o They may produce new allergens and toxins o May spread harmful traits to non-GMO crops Overuse of herbicide-tolerant GE crops has spurred an increase in herbicide use and an epidemic of herbicide-resistant "superweeds," o The long-term impacts of GMOs are unknown o Once released into the environment they cannot be recalled. 12.4 Genomics and Proteomics Genomics o Study of genomes Human and other organisms Coding and noncoding segments Human Genome Project o 13-year effort to map all the human genes and determine the nucleotide sequence of the entire human genome o Found many small regions of DNA vary among individuals o Some individuals even have extra copies of genes. o Differences may have no effect or may increase or decrease susceptibility to disease. Genome comparisons o Gives clues to evolutionary origins o Genes of humans and chimps 98% alike Humans and mice 85% alike Humans also share genes with bacteria. o Comparing human and chimp chromosome 22 Among the genes that differed were several that may have played a role in human evolution. Speech, hearing, and smell Comparing genomes may be a way of finding genes associated with human diseases. Proteomics o Explores structure and function of cellular proteins and how they interact to produce traits Important in drug development Bioinformatics o Application of computer technologies to study genome and proteome Using computer to analyze large amount of data to find significant patterns Biology 111: Concepts of Biology Chapter 13 13.1 Genes and Gene Mutations Change in the sequence of bases in a gene Causes o Replication error Rare, due to proofreading o Transposons “Jumping genes” Pieces of DNA that move within and between chromosomes o Mutagens Environmental influences like radiation Chemical mutagens Repair enzymes Types and effects of mutations Many mutations go undetected because there is no observable effect Point mutations o Change in single DNA nucleotide o Results can be minor or severe o Sickle cell disease o Three possible results of a point mutation (substitution mutation) Silent Codes for same amino acid Missense Swap one amino acid for another Nonsense Codes for a stop codon Frameshift mutations o Extra or missing nucleotides o Usually much more severe o All downstream codons affected o Two types of frameshift mutation Insertion Deletion How to think of mutations in terms of substitutions, insertions, and deletions… Think of the original sentence o The big red pig ate the red rag. A single substitution, say at the end of the third word makes the sentence: o The big rep pig ate the red rag. An insertion at the same point changes this to: o The big res dpi gat eth ere dra g. A deletion makes the sentence: o The big rep iga tet her edr ag. Here they are all together o The big red pig ate the red rag. o The big rep pig ate the red rag o The big res dpi gat eth ere dra g. o The big rep iga tet her edr ag. 13.2 Chromosomal Mutations Chromosomal mutations o In humans, only a few variations in number are typically seen. Down syndrome, Turner syndrome, Klinefelter syndrome o Changes in chromosome structure are more common. Due to breakage and failure to reunite properly Results in deletion, duplication, translocation, or inversion Deletion o When a single break causes a chromosome to lose an end or 2 breaks result in the loss of an internal segment o Williams syndrome Chromosome 7 loses a tiny end piece o Cri du chat Chromosome 5 loses an end piece Duplication o Chromosome segment repeated o Individual has more than 2 alleles for certain traits o Inv dup 15 syndrome Inverted duplication of chromosome 15 Inversion: segment joins in direction opposite from normal Translocation o Exchange of chromosome segments between two non-homologous chromosomes o A person with both of the involved chromosomes has a normal amount of genetic material and is healthy unless the exchange disrupts a gene. o 5% of Down syndrome cases caused by a translocation in previous generation between chromosomes 21 and 14 Not related to parental age but is inherited o Alagille syndrome Translocation between chromosomes 2 and 20 Normal amount of genetic material but distinctive face, some abnormalities, and severe itching Translocation disrupted allele on chromosome 20 Some people may not be aware they have the syndrome until they have a child with the syndrome. Inversion o Segment of a chromosome is turned 180° o Reverse sequence of alleles can lead to altered gene activity if it disrupts control of gene expression o Usually do not cause problems o During meiosis, crossing-over can lead to recombinant chromosomes. Alignment only possible when the inverted chromosome forms a loop 13.3 Testing for Genetic Mutations Genetic counseling o Potential parents are advised on their risk of inherited disorders o Counselor helps couple understand the mode of inheritance, medical consequences of disorder, and decisions they might wish to make Karyotyping o Visual display of chromosomes arranged by size, shape, and banding pattern Can be from white blood cells or fetal cells by amniocentesis or chorionic villus sampling Amniocentesis o Sample of amniotic fluid taken o 0.3% risk of spontaneous abortion th o Not until 14–17 week of pregnancy Chorionic villus sampling o Chorionic cells from where placenta will develop o As early as 5 week of pregnancy o Greater risk of spontaneous abortion (0.8%) but earlier results Even if no chromosomal abnormality is likely, amniocentesis might still be done to perform biochemical tests for over 400 different disorders caused by specific genes. Counselor needs to know medical history of family to construct a pedigree to decide if amniocentesis, chorionic villus sampling, or other tests are needed Determines what tests are warranted Testing for a protein o Some disorders caused by a missing enzyme Test for quantity of enzyme produced Testing the DNA o Genetic marker Relies on an abnormality in the DNA sequence due to presence of abnormal allele Fragments from restriction enzyme will differ from a normal person’s results o Genetic profiling Individual’s complete genotype DNA sample applied to DNA chip DNA chip contains probes—single-stranded DNA that binds to complementary DNA from patient Binding shows patient has particular mutated genes Testing the fetus o Ultrasound Helps evaluate fetal anatomy for serious abnormalities Uses high-frequency sound waves o Testing fetal cells Cells from amniocentesis or chorionic villus sampling Fetal cells can also be collected from mother’s blood PCR used to amplify DNA, no risk to fetus Testing the embryo o Testing embryo Following in vitro fertilization, 1 cell can be removed from embryo without harm Testing the egg o Testing egg Meiosis results in single egg and 2 polar bodies o Polar bodies can be used in genetic testing o If a woman is a heterozygote, when the polar body has the defective allele, the egg must be normal 13.4 Gene Therapy Insertion of genetic material into human cells for treatment of a disorder 2 methods o Ex vivo: outside the body o In vivo: inside the body Ex vivo o Treatment of SCID Severe combined immunodeficiency Lack enzyme involved in the maturation of cells producing antibodies Bone marrow stem cells are removed and infected with RNA retrovirus carrying the gene for normal enzyme. Cells are then returned to patient o Treatment of familial hypercholesterolemia High levels of cholesterol lead to early fatal heart attacks. Small portion of liver is removed and infected with retrovirus containing normal cholesterol receptor Tissue is returned to patient In vivo o Cystic fibrosis treatment Gene needed is sprayed into the nose or delivered to lower respiratory tract Use adenoviruses or liposomes to carry gene o Poor coronary circulation treatment Vascular endothelial growth factor can cause growth of new blood vessels. Genes coding for growth factor can be injected alone, or within a virus, into the heart to stimulate branching of coronary arteries. o Rheumatoid arthritis Immune system destroys person’s own body Inject adenoviruses that contain anti-inflammatory genes into the affected joint
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