Exam 1 Study Guide
Exam 1 Study Guide 30156
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This 14 page Study Guide was uploaded by Hannah Kennedy on Saturday July 23, 2016. The Study Guide belongs to 30156 at Kent State University taught by Dr. Helen Piontkivska in Spring 2016. Since its upload, it has received 52 views. For similar materials see ELEMENTS OF GENETICS in Biological Sciences at Kent State University.
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Date Created: 07/23/16
© Hannah Kennedy, Kent State University Elements of Genetics—Exam 1 Study Guide 1. Lecture 1—Ch. 2 a. General features of chromosomes i. Key terminology: 1. Chromosomes = the structures within living cells that contain the genetic material. Genes are physically located within the structure of chromosomes 2. Chromatin = the association btwn DNA and proteins that is found within chromosomes 3. Diploid = an organism/cell that contains 2 copies of each type of chromosome (i.e. 2 sets of chromosomes) 4. Homolog = 1 of the chromosomes within the pair of homologous chromosomes 5. Allele = an alternative form a specific gene 6. Locus = the physical location of a gene within a chromosome b. Cell cycle—interphase and M phase i. Key terminology: 1. Chromatid = following chromosomal replication in eukaryotes, the 2 copies that remain attached to each other in the form of sister chromatids; 2 sister chromatids = identical copies of the same chromosome 2. Kinetochore = a group of cellular proteins that attach to the centromere during meiosis and mitosis 3. Mitotic spindle = the structure that organizes and separates chromosomes during mitosis. Has 3 types of MTs: asters (position spindle apparatus), polars (separation of the 2 poles), and kinetochores (attach to the kinetochore of sister chromatids) 4. MTOC = a site in a cell where MTs begin to grow; mitotic spindle is formed from this 5. Centrosome = a cell structure from which MTs emanate ii. Interphase stages Stage-Interphase What’s happening Addtnl info (decondensed chromosomes) G 1 growth phase - Cell prepares to - Have 4 divide chromosomes = - Cell 2n accumulates molecular changes (e.g. the synthesis of proteins) that causes it to progress through rest of cycle G = a stage in which a 0 cell will enter when it remains either permanently or for a long time S = synthesis phase - DNA replication - Have 4 © Hannah Kennedy, Kent State University (longest stage of chromosomes = interphase) 2n - The 2 homologs in each chromosome now have twice as much DNA in the cell - Cell has 2x as many chromatids than in G1 G2= checkpoint stage - Makes sure DNA - Have 4 is replicated chromosomes = properly 2n iii. Mitosis stages: (Mitosis is cellular reproduction that makes identical copies; nuclear division) Mitosis stage (divide What’s happening Addtnl info and distribute) Prophase - Chromosomes - Have 4 begin to chromosomes = condense 2n - Mitotic spindle - chromosomes begins to form have replicated - Nuclear to produce 12 membrane chromatids (1 starts to chromatid for dissociate each homolog) - Chromatids condense - Nucleolus disappears Prometaphase— - nuclear - Have 4 transition envelope breaks chromosomes = down 2n - mitotic spindle is completely formed Metaphase - Chromosomes - Have 4 align at chromosomes = metaphase plate 2n - Chromatids can now be equally distributed into 2 daughter cells Anaphase - Sister - Have 8 chromatids chromosomes = separate and 4n become daughter chromosomes © Hannah Kennedy, Kent State University and move to opposite poles of the spindle Telophase - Chromosomes - Have 4 decondense chromosomes = - Nuclear 2n membrane re- forms and produces 2 separate nuclei Cytokinesis - 2 nuclei are - have 4 segregated into chromosomes = separate 2n daughter cell - cleavage furrow forms that pinches 1 cell into 2 c. Eukaryotes vs. prokaryotes i. Differences btwn eukaryotic and prokaryotic cells: Prokaryotes Eukaryotes - Cells contain nuclei bounded by cell - Chromosomes aren’t contained within membranes a membrane-bound nucleus - No cell wall - Cell wall - Need to export their transcripts - Have transcription and translation at the same time - Have membrane-bound organelles - Have some membrane-bound (some of which have their own DNA organelles (chloroplast contain own like mitochondria) DNA) d. Chromosome types: based on length and centromere location (autosome 1 is the longest and autosome 22 is the shortes) i. Types: Name Location of Centromere Metacentric Middle Submetacentric Between the middle and the end Acrocentric Close to end p arm = small arm q arm = long arm © Hannah Kennedy, Kent State University Telocentric At the end e. Karyotyping i. Key terminology: 1. Gametes = a haploid reproductive cell that can unite with another reproductive cell to create a zygote (sperm and egg cells) 2. Germ cells = egg and sperm cells 3. Karyotype = a photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell ii. Basis of karyotyping: When a cell is getting ready to divide, they increase their diameter when shortening (condensing in prophase) which gives them distinct shapes which become visible with a light microscope iii. Karyotyping procedure: 1. Somatic cells are removed from the patient’s body → cells are treated with drugs that stimulate them to divide→ cell division is halted during mitosis → cells are centrifuged to concentrate them → concentrated portion of cells is mixed w a hypotonic soln to make the cells swell → chromosomes spread out within the cell to allow us to see them easier → cells are treated with a dye that binds to and stains chromosomes to give them a banding pattern (2 types of bands) a. Dark G-bands = heterochromatic regions = AT-rich regions i. Very few genes, replicate late, genes not expressed as often b. Lighter bands = euchromatic regions = GC-rich regions i. Have a lot of genes, replicate early, genes more often expressed iv. Medical genetics: trisomy = extra chromosome; monosomy = lost chromosome f. Meiosis: sexual reproduction, making different versions of the cell; 2 successive nuclear division that results in 4 daughter cells: diploid to haploid i. Key terminology: 1. Meiosis = a form of nuclear division in which the sorting process results in the production of haploid cells from a diploid cell 2. Haploid = phenomenon in which the gametes contain half the genetic material found in somatic cells. For a species that is diploid, a haploid gamete contains a single set of chromosomes ii. Meiosis I Meiosis I stage What’s happening Addtnl info Prophase 1 (3 - (1): Leptotene - Generally: homologous sub-stages) stage: chromosomes form pairs homology which leads to crossing search: pairing over and recombination of homologs - Bivalents = a structure begins and in which 2 pairs of replicated homologous chromosomes chromosomes have © Hannah Kennedy, Kent State University begin to synapsed aka aligned condense with each other; the # of - (2): Sygonema bivalents is = to the (Zygotene) number of haploid stage: chromosomes homologous - Synapsis = the event in chromosomes which homologous recognize each chromosomes recognize other and each other and align begin to align themselves along their themselves (i.e. lengths bivalents); - Synaptonemal complex synaptonemal = a complex of proteins complex forms that promote the between the interconnection between homologs homologous - (3): Pachynema chromosomes during stage: 2 pairs meiosis of homologous - Tetrad = the association chromosomes among 4 homologous are getting chromosomes during ready for meiosis genetic - Genetic exchange = exchange (i.e. crossing over = leads to tetrads form an exchange of genetic and genetic material dur to non-sister recombination chromatids swapping it happens) - Chiasmata = the site where crossing over occurs Prometaphase I - nuclear envelope breaks down - mitotic spindle is completely formed Metaphase I: - bivalents are - pairs of sister chromatids independent organized are aligned in a double assortment due along row to diff metaphase orientations plate Anaphase I - 2 pairs of sister chromatids within a bivalent separate from each other - homologous pair of chromatids moves to opposite pole © Hannah Kennedy, Kent State University Telophase and - decondensation - sister chromatids have Cytokinesis I: - 2 separate reached their poles reduction nuclei are - 2 cells results division formed iii. Meiosis II: sorting events that result in 4 haploid gametes→(11n): Meiosis II stage What’s happening Addtnl info Prophase II - Spindle fibers - Have 2 cells each w 2 form again at chromosomes the poles Metaphase II - Chromosomes - Each cell as 1 of each line up along homologous chromosome metaphase plate Anaphase II - Sister chromatids are pulled apart from each other and move to opp poles along spindle fiber Telophase and - Formation of 4 cytokinesis II genetically diff haploid cells iv. Mistakes in meiosis leading to chromosomal abnormalities: 1. Down syndrome = trisomy 21 2. Turner syndrome (monosomy of X chromosome) 3. Klinefelter syndrome (XXY) g. Gametogenesis: gamete formation i. Oogenesis: the production of egg cells that occurs within the oogonia 1. Process: Oogonium → (growth/maturation) primary → oocyte → (Meiosis I) → secondary oocyte and 1 polar body → (meiosis II) → ootid and 2nd polar body → (differentiation) → ovum 2. Only 1 cell will become the egg (i.e. asymmetrical division) ii. Spermatogenesis: the production of sperm that occurs within the testes glands 1. Process: Spermatogonium → (growth/maturation) → primary spermatocyte → (meiosis I) → secondary spermatocytes → (Meiosis II) → spermatids → (differentiation)→ spermatozoa 2. Every chromatid has an equal chance of becoming a sperm (i.e. equal division) © Hannah Kennedy, Kent State University 2. Lecture 2—Ch. 3 a. Mendelian genetics i. Key terminology: 1. P-generation = parental generation = the first generation in an experiment/cross (usually true-breeding) st 2. F1 generation = 1 filial generation = offspring produced because of the cross of the parental generation; all plants show phenotype of 1 but not the other 3. F2 generation = 2 nd filial generation = offspring produced because of the cross of the F1 generation ii. Law of segregation: (monohybrid cross) states that the 2 copies of a gene separate (segregate) from each other during transmission from parent to offspring; each gamete can receive dominant or recessive allele with equal 50:50 probability iii. Law of Independent Assortment: (Dihybrid cross) states that during gamete formation, pairs of genes separate independently of each other and each gamete receives one of the other allele of a particular gene independently of another gene; arises from homologs randomly assorting themselves during Metaphase I of meiosis 1. Consequence: 1 person can make many genetically diff gametes via genetic recombination 2. Revealed by a 2-factor testcross in which dihybrid individuals are mated to homozygous recessive individuals iv. 2 sources of genetic variation in humans—random mutations and sexual reproduction (3 sub-sources of sexual reproduction) Sub-source of sexual reproduction Addtnl info Independent assortment at metaphase I - important for physical fitness Random fusion of sperm and egg at - diff sets of alleles will end up in the fertilization gamete Recombination at prophase I - homologous chromosomes aligned as a tetrad exchanges genetic material during prophase I - chromosome theory of inheritance = inheritance patterns of traits can be explained by the transmission patterns of chromosomes during gametogenesis and fertilization v. Designating alleles: 2 alleles that encode the same trait are located at similar location (loci) on 2 homologous chromosome partners; in a heterozygous individual, 1 allele is dominant and the other is recesive b. Probability theory: allows us to determine the probability that a cross btwn 2 individuals will produce specific outcome number of ×theevent occured i. Probability equation: probability = thetotalnumber os possiblecases ii. Sum rule: either/or rule: states that the probability of 1+ mutually exclusive events will occur = the sum of the individual probabilities of the events 1. Ex: cross Dede Ctct X Dede Ctct. What is the probability that an offspring will have normal ears and a normal tail or droopy ears and a droopy tail. Step 1: calculate the individual probability of each phenotype by using a Punnett square (9/(9+3+3+1)) = 9/16 is the © Hannah Kennedy, Kent State University probability of normal ears and a normal tail. (1/(9+3+3+1)) = 1/16 is the probability of droopy ears and crinkly tail. Step 2: add the individual probabilities from step 1. 9/16 +1/16 = 10/16. iii. Product rule: the probability that 2+ independent events will occur is = to the products of their individual probabilities 1. Ex: cross Pp x Pp. What is the probability that the couple’s first 3 offspring will have the disease? Step 1: calculate the individual probability of this phenotype by using a Punnett square. The probability of an affected offspring is ¼. Step 2: multiply the individual probabilities. Bc it’s the first 3 offspring, multiply ¼ x ¼ x ¼ = 0.016 st 2. End what is the probability that therd offspring will be unaffected, the 2 will have the diseae, and the 3 will be unaffected? Step 1: punnet square and individual probability of each phenotype. Step 2: calculate probability of these 3 phenotypes in specified order by multiplying respected probabilities together ¾ x ¼ x ¾ = .14 iv. Branch diagram: used to visualize the results of 3+ independent loci v. Chi-square analysis: analysis to test the statistical significance of differences between observed and expected values 2 (O−E) 2 1. Equation: X =Σ E vi. O=observed data∈eachcategory vii. E = expected data in each category based on the experimenter’s hypothesis viii. Σ=¿ ∑ thiscalculation for eachcategory ix. x2 = tells us how strong the deviation from expected is; we will accept the hypothesis if its less than the alpha number and reject it if its more c. Pedigrees i. Dominant or recessive: if it doesn’t skip any generations its dominant. If it does skip generations, its recessive ii. X-linked or autosomal: if present in males mostly then its X-linked. If present in females mostly its autosomal. If dad passes to son it’s autosomal 3. Lecture 3—Ch. 4, 5, 6, and 21.1-21.3 a. Non-Mendelian phenotype ratios: proceeding chi-square tests, what if they differ from 9:3:3:1 and 3:1 ratios i. Modification of 3:1 ratio: single genes Inheritance Pattern Inheritance Description Molecular Description Incomplete - Occurs when heterozygote has a - 50% of a dominance*** phenotype that is intermediate between functional protein either corresponding homozygote (e.g. a isn’t enough to cross btwn homozygous red flower and produce the same homozygous white flower produce trait as the heterozygous pink flower offspring) homozygote - 1 allele can’t completely mask the other making 100% - leads to phenotypic ratio of 1:2:1 Codominance*** - occurs when heterozygote expresses both - codominant alleles simultaneously without forming an alleles encode intermediate phenotype proteins that - Ex: blood type groups (occurs from what function slightly kind of glycoprotein cells present on their differently from cell surface) In MN blood groups: 2 each other. different alleles, both will be present on Function of each © Hannah Kennedy, Kent State University cell surface which will render the protein in phenotype different and distinct from if we heterozygote had only 1 allele for 1 glycoprotein. L and affects phenotype N L can produce 3 possible in a unique way phenotype/genotypes (1:2:1) a. L L M b. L L N N N c. L L - Ex: ABO group of antigens (blood type) exhibits co-dominance in combination with 2+ alleles in a population: 3 alleles, I , I , I are based on surface antigen and can yield 4 possible phenotypes i. Multiple alleles = when the same gene exists in 2+ alleles within a population ii. A and B are codominant to each other (glycoprotein alleles on cell surface so both will be present in cell phenotype) iii. A and B can mask presence of O allele so that nothing is presented Phenotyp Genotype e (i.e. blood type) A - I IA - I i X-linked B B- inheritance of genes located on the X - if pair of X-linked B - I I chromosome alleles show a - I i AB A B simple - I I dominant/recessi O - ii ve relationship, dominant allele encodes functional protein and 50% of it is enough to make a dominant trait in heterozygous female Incomplete - occurs when a dominant phenotype isn’t - dominant gene penetrance*** = expressed even though an individual may be present a pattern of carries a dominant allele (Ex: a person but the protein inheritance in who carries the polydactyly allele but has encoded by the which a dominant normal # of fingers and toes) gene doesn’t allele doesn’t - a lot of loci don’t have complete exert effects. Can always control the penetrance. So someone might be positive be due to evmt or phenotype of the for cancer but never express it (this is a to other genes individual risk in the medical world) that encode - measure of penetrance described at proteins that © Hannah Kennedy, Kent State University populational level (e.g. if 60% of heteros counteract effects carrying dom allele exhibit, the trait is of protein 60% penetrant) encoded by dominant allele Sex-influenced - the effect of sex on the phenotype of the - sex hormones individual. Some alleles are recessive in 1 regulate sex and dominant in the opposite sex (Ex: molecular pattern baldness linked to testosterone) expression of - phenomenon of heterozygotes genes which can - autosomal therefore they’re not located on influence X or Y phenotypic effects of alleles Sex-limited - traits that occur in only 1 of the 2 sexes - sex hormones (ex: breast development (e.g. beard regulate development in men/ovaries in women) molecular - sexual dimorphism = species in which expression of the males and females are morphologically genes so sex distinct; sex-limited traits are responsible hormones for this primarily produced in only 1 sex are essential to produce a particular phenotype Lethal alleles*** - an allele that has the potential of causing - most commonly the death of an organism, usually inherited loss-of-function in a recessive manner; many prevent cell alleles that division encode proteins necessary for survival. Allele may be due to a mutation in a nonessential gene that changes a protein to function abnormally Overdominance - occurs bc in some genes, heterozygotes - 2 alleles produce = an inheritance can display characteristics that are more proteins with diff pattern in which a beneficial for survival in certain envmt AA sequences heterozygote is (e.g. heterozygote may be larger/more more vigorous than disease-resistant/better able to withstand either of the hard evmt conditions) correspond - Ex: sick cell disease in homozygous homozygotes individuals. Heterozygotes that are carriers of the disease are protected against malaria bc RBCs rupture when infected preventing parasite from spreading ii. Modifications of 9:3:3:1 ratio: © Hannah Kennedy, Kent State University Inheritance Pattern Description Epistasis = phenomenon - Recessive epistasis = a form of epistasis in which an in which the phenotype of individual must be homozygous for either recessive 1 gene in one locus masks allele to mask a particular phenotype another gene in another - Ex: melanin (i.e. pigment locus: making a lot, little, or locus; occurs when 2 gene intermediate pigment. Structural protein interacts w loci control the same pigment or enzyme transports pigment to hair follicle): phenotypic character— BB = black (dominant), bb = brown (recessive), Bb = occurs across 2 separate, black (dominant); c controls pigment deposition and is different loci; often occurs epistatic to B or b (i.e. pigment formation) bc 2+ diff protein o cc = albino whether it is BBcc or bbcc participate in common - Ex: breeding Labrador Retrievers –9:3:4 ratio function (e.g. 2+ proteins o Have 2 loci responsible; will be dependent upon may be part of an if there exists 2 dominant or 2 recessive alleles enzymatic pathway that in these loci lead to the formation of a P: Black (BBEE) x Yellow (bbee) single product) F1: Black (BbEe) F2: 895 black, 280 brown, and 425 yellow (Do a chi-square test to see if this is a 9:3:4 or a 9:3:3:1: set up both and see which hypothesis will be accepted or rejected) - Diff kinds of epistasis: Ratio Genotype Type of Interaction 9:3:3:1*** - 9 A_B_ None - 3 A_bb - 3 aaB_ - 1 aabb 9:3:4 - 9 A_B_ Recessive epistasis - 3 A_bb - 4 aaB_ 12:3:1 - 12 A_B_ Dominant - 3 aaB_ epistasis - 1 aabb Complementation = a - 2 diff parents that express the same or similar phenomenon in which the recessive phenotypes produce offspring with a wild- presence of 2 diff mutant type phenotype alleles in the same - each recessive allele is complemented by a wild-type organism produces a wild- allele which indicates recessive alleles are in diff type phenotype. It occurs genes usually bc the 2 mutation are in diff genes, so the organism carries 1 copy of each mutant allele and 1 copy of each wild-type allele iv. combinations of inheritance patterns: if both/either loci have multiple alleles in a population: Ex: AaI I x AaI I This is a cross that involves 2 traits: ABO blood type (found at 1 locus, alleles I and I ). Albinism (found at second locus, alleles A and a) d. Differences between sexes/sex chromosomes © Hannah Kennedy, Kent State University i. Key terminology: 1. Chromosome theory of inheritance = state that chromosomes carry the genes that determine an organism’s traits 2. Autosomes = chromosomes that aren’t sex chromosomes 3. X-linked alleles = genes (or alleles of genes) that are physically located within the X chromosome 4. Testcross = an experimental cross between a recessive individual and an individual whose genotype the experimenter wishes to determine 5. X-linked recessive pattern = an allele or trait in which the gene is found on the X chromosome and the allele is recessive relative to a corresponding dominant allele (e.g. Duchenne muscular dystrophy) ii. X-inactivation: 1. Key terminology: a. Dosage compensation = the phenomenon in which the level of expression of many genes on the sex chromosomes (i.e. the X chromosome) is similar in both sexes, even though males and females have a different complement of sex chromosomes. b. X inactivation = a process in which mammals equalize the expression of X-linked genes by randomly turning off 1 X chromosome in the somatic cells of females c. X-inactivation center = Xic = a site on the X chromosome that appears to play a critical role in X inactivation; counting X chromosomes is done by counting Xics; must be found on X chromosome for inactivation to occur d. Barr body = the inactivated X chromosome 2. Example: Calico cat: female cats are mosaic: half their cells have an active black X and half have an active red X. Only heterozygous females can be calico. So, for a black and orange fur on a cat, the orange patches are due to the inactivation of the X chromosome that carries the black allele and the black patches are due to the inactivation of the X chromosome that carries the orange allele 3. Process: Expression of specific gene within Xic is required for the X chromosome to compact into Barr body. Gene is Xist = X-inactive specific transcript. Xist gene on the inactivated X chromosome is active. Xist gene produces RNA molecule that doesn’t encode a protein. RNA coats X chromosome and inactivate it. Protein then associate with Xist RNA and promote chromosomal compaction into Barr body. e. Ch. 6—extranuclear inheritance, imprinting, and maternal effect i. Key terminology: 1. Extranuclear inheritance: inheritance of organellar genetic material 2. Maternal inheritance: inheritance that occurs bc the chloroplasts are inherited only through the cytoplasm of the egg 3. Heteroplasmy: a cell may contain more than 1 type of chloroplast or mitochondria 4. Nucleoid: location of chromosomes in mitochondria and chloroplasts 5. Paternal leakage: paternal parent may occasionally provide mitochondria via the sperm 6. Maternal inheritance: the mode of mitochondrial transmission in most species © Hannah Kennedy, Kent State University 7. Epigenetic inheritance: inheritance patterns which are the result of DNA and chromosomal modifications that occur during oogenesis, spermatogenesis, or early stages of embryogenesis 8. Genomic imprinting: inheritance in which a segment of DNA is marked, and that mark is retained and recognized throughout the life of the organism inheriting the marked DNA ii. Extranuclear inheritance of chloroplasts: chloroplasts were probably derived from an endosymbiotic relationship btwn cyanobacteria and a eukaryotic cell iii. Extranuclear inheritance of mitochondria: mitochondria were probably derived from gram negative non-sulfur purple bacteria and a eukaryotic cell iv. Epigenetics and imprinting: 1. Key terminology a. DNA methylation = the phenomenon in which an enzyme covalently attaches a methyl group to a base in DNA (a or c) to regulate gene expression (usually inhibits it) b. Imprinting control region = ICR = DNA region that is differentially methylated and plays a role in genomic imprinting; contains binding sites for 1 or more proteins that regulate the transcription of the imprinted gene i. When ICR is not methylated, CTC-binding factor can bind and cause 2 things 1. Prevents activator proteins from activating certain gene and shutting it off 2. Permits activator proteins to turn on specific gene v. Maternal effect: an in heritance pattern for certain nuclear genes in which the genotype of the mom directly determines the phenotype of the offspring 1. Process: as an oocyte (i.e. egg) matures, surrounding maternal cells provide egg with nutrients. these nurse cells produce both gene products (mRNA and/or proteins) that are then transported into the egg. egg can receive whatever it wants (gene products of the nurse cells reflect the genotype of the mother and influence early developmental stages of the embryo). maternal effect genes encode proteins that are impt in early steps of embryogenesis; play role in cell division, cleavage pattern, and body axis orientation f. Ch. 21.1-21.3 i. Inheritance patterns of genetic diseases: Inheritance pattern Description Autosomal recessive - affected offspring may have 2 unaffected inheritance parents - common for genetic disorders that involve defective enzymes - genetic sequence that creates a loss-of- function allele; causes a reduction or loss of function in the encoded protein Autosomal - affected offspring usually has 1/both affected dominant parents inheritance - due to 3 things: (1): haploinsufficiency = the phenomenon in which a person has only a single functional copy of a gene, and that single functional copy doesn’t result in a normal phenotype; 50% of the functional protein isn’t sufficient to produce a normal phenotype (2): gain-of-function mutations © Hannah Kennedy, Kent State University = the phenomenon in which a person has only a single functional copy of a gene, and that single functional copy doesn’t result in a normal phenotype; 50% of the functional protein isn’t sufficient to produce a normal phenotype (3): dominant-negative mutations = a mutation that produces an altered gene product that acts antagonistically to the normal gene product X-linked recessive - males are hemizygous for these genes inheritance - males exhibit the trait most likely X-linked dominant - males are more severely affected so they die inheritance and females exhibit it ii. detection of disease-causing alleles: 1. Key terminology: a. Haplotype = haploid genotype = the linkage of alleles of molecular markers along a small region of a single chromosome 1. Haplotype association study: a study in which disease-causing alleles are ID’d due to their linkage to particular markers along a chromosome; based on 2 things: a. (1): allele that causes disease has its origin in a single individual (i.e. founder) who lived a long time ago and since them the allele has spread throughout portions of population. b. (2): When disease-causing allele originated in the founder, it occurred in a region with a specific haplotype that didn’t change. (Ppl with the same haplotype as found (e.g. 1A, 2C, 3B, 4B) is more likely to get the allele) ii. Genetic testing done before birth: 3 common ways 1. amniocentesis = process of genetic testing in which a doctor removes amniotic fluid that contains fetal cells by using a needle that passes through the abdominal wall; cell sample then is tested like karyotyping 2. chorionic villus sampling = CVS = process of genetic testing in which a small piece of the chorion (i.e. the fetal part of the placenta) is removed and genetic testing is done on cell sample; can be performed earlier than amniocentesis 3. preimplantation genetic diagnosis = PGD = a time of genetic screening prior to birth in which is conducted before pregnancy to test the embryos made by IVF to check for a specific genetic abnormality (e.g. allele that causes HD) iii. Prions: proteinaceous disease-causing agents that cause several types of neurodegenerative diseases 1. ability of the prion protein to exist in 2 conformations: C a. PrP (Scesn’t cause disease) b. PrP (abnormal, causes disease; acts as a catalyst to convert normal prions to misfolded ones. Form aggregated in brain cells and PNS tissues)
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