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Genetics & The Work of Mendel AP Biology 2006-2007 Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas used experimental method used quantitative analysis collected data & counted them AP Biology excellent example of scientific method Mendel’s work Bred pea plants cross-pollinate True breeding parents (P) (All offspring like the parents) P = parental raised seeds & then observed traits (F1) F = filial allowed offspring to self-pollinate & observed next generation (F2) Used mathematical principals of probability to interpret results (studies 2 generations) AP Biology Mendel collected data for 7 pea traits AP Biology Looking closer at Mendel’s work P F1 true-breeding true-breeding X purple-flower peas white-flower peas 100% purple-flower peas Where did the white flowers go? 100% generation (hybrids) self-pollinate F2 generation AP Biology 75% purple-flower peas White flowers came back! 25% white-flower peas 3:1 What did Mendel’s findings mean? Traits come in alternative versions purple vs. white flower color Alternate versions of a gene called alleles different alleles vary in the sequence of nucleotides at the specific locus of a gene some difference in sequence of A, T, C, G purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of gene at same location on homologous chromosomes AP Biology Traits are inherited as discrete units For each characteristic, an organism inherits 2 alleles, 1 from each parent diploid organism inherits 1 set of chromosomes from each parent homologous chromosomes Diploid = 2 sets of chromosomes like having 2 editions of encyclopedia AP Biology What are the advantages of being diploid? What did Mendel’s findings mean? Some traits mask others purple & white flower colors are separate traits that do not blend purple x white ≠ light purple purple masked white dominant allele functional protein masks other alleles Designated with an upper case letter recessive allele malfunctioning protein Effect only exerted in homozygous state Designated with a lower case letter AP Biology Genotype vs. phenotype Difference between how an organism “looks” & its genetics phenotype description of an organism’s trait genotype description of an organism’s genetic makeup X P Explain Mendel’s results using …dominant & recessive purple white F1 AP Biology all purple Making crosses Can represent alleles as letters flower color alleles P or p true-breeding purple-flower peas PP true-breeding white-flower peas pp AP Biology Genotypes Homozygous = same alleles = PP, pp Heterozygous = different alleles = Pp homozygous dominant heterozygous homozygous recessive AP Biology Phenotype vs. genotype 2 organisms can have the same phenotype but have different genotypes Can’t tell by lookin’ at ya! How do you determine the genotype of an individual with with a dominant phenotype? AP Biology Test cross Breed the dominant phenotype — the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele How does that work? x is it PP or Pp? AP Biology pp Mendel chose peas luckily Pea plants are good for genetic research Relatively simple genetically Most characters are controlled by a single gene pair Each gene has only 2 alleles, one of which is completely dominant to the other AP Biology Mendel chose peas luckily Mendel had strict control over which plants mated with which Each pea plant has male & female structures Pea plants can self-pollinate Mendel could also cross-pollinate plants: moving pollen from one plant to another AP Biology 1st law Mendel’s of heredity Law of segregation P PP P When gametes (eggs and sperm) are produced during meiosis during meiosis, alleles segregate from each other pp each allele for a trait is packaged into a separate gamete(egg or sperm) p p P Pp p AP Biology Law of Segregation Which stage of meiosis creates the law of segregation? Whoa! And Mendel didn’t even know DNA or genes existed! AP Biology Monohybrid cross Some of Mendel’s experiments followed the inheritance of single characters AP Biology Ex: flower height TT X tt Tt X Tt Tt X TT AP Biology Dihybrid cross Other of Mendel’s experiments followed the inheritance of 2 different characters AP Biology seed color and seed shape Mendel was working out many of the genetic rules! YYRR X yyrr AP Biology Mendel’s 2nd law of heredity Can you think of an exception to this? Law of independent assortment Each pair of alleles- for each trait- separate into gametes independently non-homologous chromosomes align independently 4 classes of gametes produced in equal amounts YR = Yr = yR = yr only true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequently YyRr YR Yr AP Biology yR yr YR Yr yR yr Law of Independent Assortment Which stage of meiosis creates the law of independent assortment? Remember Mendel didn’t even know DNA —or genes— existed! AP Biology Metaphase 1 EXCEPTION If genes are on same chromosome & close together will usually be inherited together rarely crossover separately “linked” The chromosomal basis of Mendel’s laws… Trace the genetic events through meiosis, gamete formation & fertilization to offspring AP Biology Probability & Genetics AP Biology 2006- Genetics & Probability Mendel’s laws: segregation independent assortment reflect same laws of probability that apply to tossing coins or rolling dice AP Biology Probability & genetics Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin probability of tossing heads? probability making a B gamete? B 100% BB B AP Biology B 50% Bb b Probability & genetics Outcome of 1 toss has no impact on the outcome of the next toss probability of tossing heads each time? 50% probability making a B gamete each time? 50% B Bb b AP Biology Rule of multiplication Chance that 2 or more independent events will occur together probability that 2 coins tossed at the same time will land heads up 1/2 x 1/2 = 1/4 probability of Pp x Pp pp 1/2 x 1/2 = 1/4 P Pp p AP Biology Calculating dihybrid probability Use rule of multiplication to predict crosses YyRr x YyRr x Yy Yy Rr yyrr x ?% 1/16 yy AP Biology rr 1/4 x 1/4 Rr Apply the Rule of Multiplicationnot in lecture AABbccDdEEFf x AaBbccDdeeFf AabbccDdEeFF Got it? Try this! AP Biology AA x Aa Aa Bb x Bb bb cc x cc cc Dd x Dd Dd EE x ee Ee Ff x Ff FF 1/2 1/4 1 1/2 1 1/4 1/64 Rule of addition Chance that an event can occur 2 or more different ways sum of the separate probabilities probability of Bb x Bb BB or bb sperm egg offspring B B BB 1/2 x 1/2 = b b 1/2 x 1/2 = AP Biology 1/4 bb 1/4 1/4 + 1/4 1/2 Chi-square test Test to see if your data supports your hypothesis Compare “observed” vs. “expected” data is variance from expected due to “random chance”? or is there another factor influencing data? null hypothesis degrees of freedom statistical significance AP Biology AP Biology AP Biology Beyond Mendel’s Laws of Inheritance AP Biology 2006- Extending Mendelian genetics Mendel worked with a simple system peas are genetically simple most traits are controlled by a single gene each gene has only 2 alleles, 1 of which is completely dominant to the other The relationship between genotype & phenotype is rarely that simple AP Biology Incomplete dominance Heterozygote shows an intermediate, blended phenotype example: RR = red flowers RR WW = white flowers WW RW = pink flowers RW make 50% less color AP Biology RR RW WW Incomplete dominance P X true-breeding red flowers true-breeding white flowers 100% pink flowers F1 100% generation (hybrids) self-pollinate 25% red F2 generation AP Biology 50% pink 25% white It’s like flipping 2 pennies! 1:2:1 Co-dominance 2 alleles affect the phenotype equally & separately not blended phenotype human ABO blood groups 3 alleles IA, IB, i0 IA & IB alleles are co-dominant glycoprotein antigens on RBC i0 allele recessive to both AP Biology Genetics of Blood type phenogenotype type A B AB O AP Biology antigen on RBC antibodies in blood donation status IA IA or IA i type A antigens on surface of RBC anti-B antibodies __ IB IB or IB i type B antigens on surface of RBC anti-A antibodies __ IA IB both type A & type B antigens on surface of RBC no antibodies universal recipient ii no antigens on surface of RBC anti-A & anti-B antibodies universal donor Blood compatibility Matching compatible blood groups is critical for blood transfusions. A person produces antibodies against foreign blood factors = glycoproteins (donor blood). If donor’s blood has an A or B oligosaccharide that is foreign to the recipient, antibodies in the recipient’s blood will bind to the foreign molecules. Cause the donated blood cells to clump AP Biology together & can kill the recipient. Multiple Alleles Three or more alternative forms of a gene (alleles) that can occupy the same locus. However, only two of the alleles can be present in a single organism. For example: the ABO system of blood groups is controlled by three alleles, only two of which are present in an individual. AP Biology Incomplete Penetrance: Offspring does not always show dominant trait or the level of expression. I.E. Polydactly AP Biology Pleiotropy Most genes are pleiotropic one gene affects more than one phenotypic character 1 gene affects more than 1 trait dwarfism (achondroplasia) gigantism (acromegaly) AP Biology Inheritance pattern of Achondroplasia Aa x aa Aa x Aa dominant inheritance A a a a Aa Aa dwarf dwarf aa aa 50% dwarf:50% AP Biology normal or 1:1 A A a AA Aa lethal a Aa aa 67% dwarf:33% normal or 2:1 Pleiotrophy Cont. Gigantism (acromegaly) AP Biology Marfan Syndrome Mutated gene on chromosome 15 AP Biology Disproportionately long arms, legs, hands, feet, weakened aorta, poor eyesight Epistasis One gene completely masks another gene coat color in mice = 2 separate genes C,c: B_C_ bbC_ _ _cc AP Biology pigment (C) or no pigment (c) B,b: more pigment (black=B) or less (brown=b) cc = albino, no matter B allele 9:3:3:1 becomes 9:3:4 How would you know that difference wasn’t random chance? Chi-square test! Epistasis in Labrador retrievers 2 genes: (E,e) & (B,b) pigment (E) or no pigment (e) pigment concentration: black (B) to brown (b) eebb AP Biology eeB– E–bb E–B– Polygenic inheritance Some phenotypes determined by additive effects of 2 or more genes on a single character phenotypes on a continuum human traits skin color - dominant alleles have a quantitative effect…each adds to the effect height weight intelligence AP Biology behaviors Skin color: Albinism Johnny & Edgar Winter However albinism can be inherited as a single gene trait aa = albino albino Africans melanin = universal brown color enzyme tyrosine AP Biology melanin albinism OCA1 albino AP Biology Bianca Knowlton Nature vs. Nurture Phenotype is controlled by both environment & genes A single tree has leaves that vary in size, shape & color, depending on exposure to wind & sun For humans, nutrition influences height, exercise alters build, sun tanning darkens the skin, and experience improves performance on intelligence tests Even identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiences AP Biology Pleiotrophy Cont. Gigantism (acromegaly) AP Biology Multiple Alleles Three or more alternative forms of a gene (alleles) that can occupy the same locus. However, only two of the alleles can be present in a single organism. For example: the ABO system of blood groups is controlled by three alleles, only two of which are present in an individual. AP Biology Sex linked traits 1910 | 1933 Genes are on sex chromosomes as opposed to autosomal chromosomes discovered by T.H. Morgan 1st to associate a specific gene with a specific chromosome AP Biology Classes of chromosomes autosomal chromosomes sex chromosomes AP Biology Sex linked traits Drosophila breeding - good genetic subject AP Biology 1910 | 1933 Prolific, females mate once & lay hundreds of eggs Short 2 week generations Only 4 pairs of chromosomes XX=female, XY=male (Like humans) Discovery of sex linkage P true-breeding red-eye female “Wild Type” F1 X true-breeding Mutant white-eye male 100% red eye offspring Huh! Sex matters?! generation (hybrids) F2 generation AP Biology 100% red-eye female 50% red-eye male 50% white eye male What’s up with Morgan’s flies? x RR r R Rr x rr Rr r Rr Rr R R r RR Rr Rr rr Doesn’t work that way! R AP Biology Rr Rr 100% red eyes r 3 red : 1 white Genetics of Sex In humans & other mammals, there are 2 sex chromosomes: X & Y 2 X chromosomes develop as a female: XX gene redundancy, like autosomal chromosomes an X & Y chromosome X Y X XX XY X XX XY develop as a male: XY no redundancy AP Biology 50% female : 50% male Let’s reconsider Morgan’s flies… x XR XR Xr XR XR AP Biology XR Xr XR Xr x XrY XR Xr Y XRY XRY 100% red eyes XR BINGO! Xr XRY XR Y XR XR XRY XR Xr X rY 100% red females 50% red males; 50% white males Genes on sex chromosomes Y chromosome few genes other than SRY sex-determining region master regulator for maleness turns on genes for production of male hormones many effects = pleiotropy! X chromosome AP Biology other genes/traits beyond sex determination Human X chromosome Sex-linked Duchenne muscular dystrophy Becker muscular dystrophy usually means “X-linked” more than 60 diseases traced to genes on X chromosome Chronic granulomatous disease Retinitis pigmentosa-3 Norrie disease Retinitis pigmentosa-2 Hypophosphatemia Aicardi syndrome Hypomagnesemia, X-linked Ocular albinism Retinoschisis Adrenal hypoplasia Glycerol kinase deficiency Ornithine transcarbamylase deficiency Incontinentia pigmenti Wiskott-Aldrich syndrome Menkes syndrome Androgen insensitivity Sideroblastic anemia Aarskog-Scott syndrome PGK deficiency hemolytic anemia Anhidrotic ectodermal dysplasia Agammaglobulinemia Kennedy disease Pelizaeus-Merzbacher disease Alport syndrome Fabry disease Immunodeficiency, X-linked, with hyper IgM Lymphoproliferative syndrome Albinism-deafness syndrome Fragile-X syndrome AP Biology Ichthyosis, X-linked Placental steroid sulfatase deficiency Kallmann syndrome Chondrodysplasia punctata, X-linked recessive Charcot-Marie-Tooth neuropathy Choroideremia Cleft palate, X-linked Spastic paraplegia, X-linked, uncomplicated Deafness with stapes fixation PRPS-related gout Lowe syndrome Lesch-Nyhan syndrome HPRT-related gout Hunter syndrome Hemophilia B Hemophilia A G6PD deficiency: favism Drug-sensitive anemia Chronic hemolytic anemia Manic-depressive illness, X-linked Colorblindness, (several forms) Dyskeratosis congenita TKCR syndrome Adrenoleukodystrophy Adrenomyeloneuropathy Emery-Dreifuss muscular dystrophy Diabetes insipidus, renal Myotubular myopathy, X-linked Human X-Linked Disorders 1. More males have X-linked traits because recessive alleles on the X chromosome in males are expressed in males. 2. Color Blindness can be an X-linked recessive disorder involving mutations of genes coding for green or red sensitive cone cells, resulting in the inability to perceive green or red, respectively; the pigment for blue-sensitive protein is autosomal. About 8% of Caucasian men have red-green color blindness.. AP Biology Human X-Linked Disorders Muscular Dystrophy a. Duchenne muscular dystrophy is the most common form and is characterized by wasting away of muscles, eventually leading to death; it affects one out of every 3,600 male births. b. This X-linked recessive disease involves a mutant gene that fails to produce the protein dystrophin. c. Signs and symptoms (e.g., waddling gait, toe walking, frequent falls, difficulty in rising) soon appear. D. Muscles weaken until the individual is confined to a wheelchair; death usually occurs by age 20. AP Biology Human X-Linked Disorders e. Affected males are rarely fathers; the gene passes from carrier mother to carrier daughter. f. Lack of dystrophin protein causes calcium ions to leak into muscle cells; this promotes action of an enzyme that dissolves muscle fibers. g. As the body attempts to repair tissue, fibrous tissue forms and cuts off blood supply to the affected muscles. h. A test now detects carriers of Duchenne muscular dystrophy; treatments are being attempted. AP Biology sex-linked recessive Hemophilia H Xh x X HY HH XHh XH female / eggs male / sperm XH XH Y XH XH XH Y XH Xh Xh XH Xh AP Biology XH Xh XhY carrier disease XHY Y Human X-Linked Disorders Hemophilia a.About one in 10,000 males is a hemophiliac with impaired ability of blood to clot. b. The two common types: Hemophilia A, due to the absence of clotting factor IX; Hemophilia B, due to the absence of clotting factor VIII. c. Hemophiliacs bleed externally after an injury and also suffer internal bleeding AP Biology around joints. Human X-Linked Disorders d. Hemorrhages stop with transfusions of blood (or plasma) or concentrates of clotting protein. e. Factor VIII is now available as a genetically-engineered product. f. Of Queen Victoria’s 26 offspring, five grandsons had hemophilia and four granddaughters were carriers. AP Biology AP Biology Pedigree Practice AP Biology Pedigree Practice AP Biology Map of Human Y chromosome? < 30 genes on Y chromosome Sex-determining Region Y (SRY) Channel Flipping (FLP) Catching & Throwing (BLZ-1) Self confidence (BLZ-2) Devotion to sports (BUD-E) Addiction to death & destruction movies (SAW-2) note: not linked to ability gene Air guitar (RIF) Scratching (ITCH-E) Spitting (P2E) Inability to express affection over phone (ME-2) AP Biology linked Selective hearing loss (HUH) Total lack of recall for dates (OOPS) Sex-linked traits summary X-linked Follow the X chromosomes Males get their X from their mother (female carriers) Trait is never passed from father to son Y-linked Very few traits Only 26 genes Trait is only passed from father to son Females cannot inherit AP Biology Chromosomal conditions involving the sex chromosomes often affect sex determination (whether a person has the sexual characteristics of a male or a female), sexual development, and the ability to have children (fertility). The signs and symptoms of these conditions vary widely and range from mild to severe. They can be caused by missing or extra copies of the sex chromosomes or by structural changes in these chromosomes. AP Biology X-inactivation Female mammals inherit 2X chromosomes one X becomes inactivated during embryonic development condenses into compact object = Barr body which X becomes Barr body is random patchwork trait = “mosaic” patches of black XH XH Xh tricolor cats can only be AP Biology female Xh patches of orange Male pattern baldness Sex influenced trait autosomal trait influenced by sex hormones age effect as well = onset after 30 years old dominant in males & recessive in females B_ = bald in males; bb = bald in females AP Biology Environmental effects Phenotype is controlled by both environment & genes Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive alleles Color of Hydrangea flowers APinfluenced Biology is by soil pH Any Questions? AP Biology 2006- Studying Inheritance in Humans 1 AP Biology 3 4 2 5 2006-2007 6 Pedigree analysis Pedigree analysis reveals Mendelian patterns in human inheritance = male AP Biology data mapped on a family tree = female = male w/ trait = female w/ trait Simple pedigree analysis 11 33 AP Biology 44 What’s the likely inheritance pattern? 22 55 66 Genetic counseling Pedigree can help us understand the past & predict the future Thousands of genetic disorders are inherited as simple recessive traits from benign conditions to deadly diseases albinism cystic fibrosis Tay sachs sickle cell anemia PKU AP Biology Genetic testing CVS –Chorionic Villus Sampling sequence individual genes AP Biology Recessive diseases The diseases are recessive because the allele codes for either a malfunctioning protein or no protein at all Heterozygotes (Aa) carriers have a normal phenotype because one “normal” allele produces enough of the required protein AP Biology Heterozygote crosses Heterozygotes as carriers of recessive alleles Aa x Aa female / eggs male / sperm A a AP Biology A a AA AA Aa Aa A Aa a carrier Aa Aa aa carrier disease A Aa a Cystic fibrosis (recessive) Primarily whites of European descent strikes 1 in 2500 births 1 in 25 whites is a carrier (Aa) normal lung tissue normal allele codes for a membrane protein that transports Cl- across cell membrane defective or absent channels limit transport of Cl- & H2O across cell membrane thicker & stickier mucus coats around cells mucus build-up in the pancreas, lungs, digestive tract & causes bacterial infections AP Biology without treatment children die before 5; with treatment can live past their late 20s Chloride channel Effect on Lungs normal lungs airway Cl– transports salt through protein channel out of cell Osmosis: H2O follows Cl– Cl– channel H 2O cells lining lungs cystic fibrosis Cl– H 2O bacteria & mucus build up thickened mucus hard to secrete AP Biology mucus secreting glands delta F508 loss of one amino acid AP Biology Tay-Sachs (recessive) Primarily Jews of eastern European (Ashkenazi) descent & Cajuns (Louisiana) strikes 1 in 3600 births 100 times greater than incidence among non-Jews non-functional enzyme fails to breakdown lipids in brain cells fats collect in cells destroying their function symptoms begin few months after birth seizures, blindness & degeneration of muscle & mental performance child usually dies before 5yo AP Biology Sickle cell anemia (recessive) Primarily Africans strikes 1 out of 400 African Americans high frequency caused by substitution of a single amino acid in hemoglobin when oxygen levels are low, sickle-cell hemoglobin crystallizes into long rods deforms red blood cells into sickle shape sickling creates pleiotropic effects = cascade of other symptoms AP Biology Sickle cell anemia Substitution of one amino acid in polypeptide chain AP Biology hydrophilic amino acid hydrophobic amino acid AP Biology Sickle cell phenotype 2 alleles are codominant both normal & mutant hemoglobins are synthesized in heterozygote (Aa) 50% cells sickle; 50% cells normal carriers usually healthy sickle-cell disease triggered under blood oxygen stress exercise AP Biology Heterozygote advantage Malaria single-celled eukaryote parasite spends part of its life cycle in red blood cells Sickle cell frequency High frequency of heterozygotes is unusual for allele with severe detrimental effects in homozygotes. 1 out of 400 African Americans Suggests some selective advantage of being heterozygous. AP Biology Heterozygote advantage In tropical Africa, where malaria is common: homozygous dominant individuals die of malaria homozygous recessive individuals die of sickle cell anemia heterozygote carriers are relatively free of both reproductive advantage High frequency of sickle cell allele in African Americans is vestige of African roots• AP Biology Prevalence of Malaria Prevalence of Sickle Cell Anemia AP Biology Huntington’s chorea (dominant) Dominant inheritance Testing… Would you want to know? 1872 repeated mutation on end of chromosome 4 mutation = CAG repeats glutamine amino acid repeats in protein one of 1st genes to be identified build up of “huntingtin” protein in brain causing cell death memory loss muscle tremors, jerky movements “chorea” starts at age 30-50 early death 10-20 years after start AP Biology Genetics & culture Why do all cultures have a taboo against incest? laws or cultural taboos forbidding marriages between close relatives are fairly universal Fairly unlikely that 2 unrelated carriers of same rare harmful recessive allele will meet & mate AP Biology but matings between close relatives increase risk “consanguineous” (same blood) matings individuals who share a recent common ancestor are more likely to carry same recessive alleles A hidden disease reveals itself Aa x Aa male / sperm male / sperm A A A a A AA AA A AA Aa a Aa Aa a Aa aa AP Biology female / eggs female / eggs AA x Aa • increase carriers in population • hidden disease is revealed Any questions? AP Biology 2006-2007 Errors of Meiosis Chromosomal Abnormalities AP Biology 2006-2007 Chromosomal abnormalities Incorrect number of chromosomes nondisjunction chromosomes don’t separate properly during meiosis breakage of chromosomes deletion duplication inversion translocation AP Biology Nondisjunction Problems with meiotic spindle cause errors in daughter cells 2n Tetrad chromosomes do not separate properly during Meiosis 1 sister chromatids fail to separate during Meiosis 2 too many or too few chromosomes n-1 n n+1 n AP Biology Alteration of chromosome number error in Meiosis 1 error in Meiosis 2 all with incorrect number AP Biology 1/2 with incorrect number Nondisjunction Baby has wrong chromosome number trisomy cells have 3 copies of a chromosome n+1 AP Biology monosomy cells have only 1 copy of a chromosome n-1 n n trisomy monosomy 2n+1 2n-1 Human chromosome disorders High frequency in humans most embryos are spontaneously aborted alterations are too disastrous developmental problems result from biochemical imbalance Certain conditions are tolerated AP Biology upset the balance less = survivable but characteristic set of symptoms = syndrome Down syndrome Trisomy 21 3 copies of chromosome 21 1 in 700 children born in U.S. Chromosome 21 is the smallest human chromosome but still severe effects Frequency of Down syndrome correlates with the age of the mother AP Biology Down syndrome & age of mother Mother’s age Incidence of Down Syndrome Under 30 <1 in 1000 30 1 in 900 35 1 in 400 36 1 in 300 37 1 in 230 38 1 in 180 39 1 in 135 40 1 in 105 42 1 in 60 44 1 in 35 46 1 in 20 48 1 in 16 49 1 in 12 AP Biology Rate of miscarriage due to amniocentesis: 1970s data 0.5%, or 1 in 200 pregnancies 2006 data <0.1%, or 1 in 1600 pregnancies Genetic testing Amniocentesis in 2nd trimester sample of embryo cells stain & photograph chromosomes Analysis of karyotype CVS – Chorionic Villus Sampling AP Biology Sex chromosomes abnormalities Human development more tolerant of wrong numbers in sex chromosome But produces a variety of distinct syndromes in humans AP Biology XXY = Klinefelter’s syndrome male XXX = Trisomy X female XYY = Jacob’s syndrome male XO = Turner syndrome female Klinefelter’s syndrome XXY male one in every 2000 live births have male sex organs, but are sterile feminine characteristics some breast development lack of facial hair tall normal intelligence AP Biology Klinefelter’s syndrome AP Biology Jacob’s syndrome male XYY Males 1 in 1000 live male births extra Y chromosome slightly taller than average more active normal intelligence, slight learning disabilities delayed emotional maturity normal sexual development AP Biology Trisomy X XXX 1 in every 2000 live births produces healthy females Why? Barr bodies all but one X chromosome is inactivated AP Biology Turner syndrome Monosomy X or X0 1 in every 5000 births varied degree of effects webbed neck short stature sterile AP Biology error of replication Changes in chromosome structure deletion duplication error of crossing over loss of a chromosomal segment repeat a segment inversion reverses a segment translocation AP Biology move segment from one chromosome to another Don’t hide… Ask Questions!! AP Biology 2006-2007