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Introduction to Genetics and Human Genetics Chapters 11.1-11.3 & 14.1-14.2 Standard #1 Determine how an organism passes its characteristics on to its offspring. (11.1) A. Describe Mendel’s studies and conclusions about inheritance. B. How does an organism get its unique characteristics? C. Explain how different forms of a gene are distributed to offspring. 1.A. Describe Mendel’s studies and conclusions about inheritance. Heredity • the transmission of characteristics from parents to offspring Genetics • the study of how characteristics are transmitted from parents to offspring and how the traits are expressed 1.A. Describe Mendel’s studies and conclusions about inheritance. Gregor Mendel (father of genetics) • observed 7 characteristics of pea plants • each had 2 contrasting traits • seeds from purple flowered plants produced purple flowered plants but some white flowered plants also were produced (why?) • to document traits of each generation, he controlled the pollination 1.A. Describe Mendel’s studies and conclusions about inheritance. Pollination • pollen grains from anthers transferred to stigma Types of pollination: • self-pollination • pollen from anther to stigma of same flower or from the another flower on the same plant (normal method) • cross-pollination • involves flowers of two separate plants 1.A. Describe Mendel’s studies and conclusions about inheritance. Why Did Mendel use pea plants? • Easy to care for • Short generation time • Many offspring each generation • Can control mating between plants • Require little space to grow • Several contrasting traits 1.A. Describe Mendel’s studies and conclusions about inheritance. Mendel's Experiments: • plants pure for each trait - always produce offspring with that trait called pure strain Terms: • P1 generation (parental) - a pure strain plant for some trait • cross-pollinated these • F1 generation (first filial) - offspring of the P1 generation • allowed these to self pollinate • F2 generation (second filial) - offspring of F1 generation 1.A. Describe Mendel’s studies and conclusions about inheritance. Mendel Results: 1.A. Describe Mendel’s studies and conclusions about inheritance. Mendel's Conclusions: • green pods X yellow pods • F1 all green pods • F1 green pod X green pod • F2: ¾ green pod : ¼ yellow pod • Factors (alleles) •something in pea plants controlling traits •hypothesized each characteristic controlled by separate factor •since each characteristic had 2 alternative forms, must be pair of factors for each trait 1.B. How does an organism get its unique characteristics? Gene • Factors that are passed from parent to offspring • segment of DNA on chromosome controlling a trait • chromosomes in pairs, so genes are in pairs Allele • the alternative forms of a gene 1.C. Explain how different forms of a gene are distributed to offspring. Law of dominance • trait appearing in F1 must be controlled by dominant factor • prevents other factor from having an effect • trait not appearing in F1 but reappearing in F2 must be controlled by recessive factor • factor hidden by dominant Law of Segregation • a pair of factors is segregated, or separated, during the formation of gametes • describes what happens in meiosis Standard 2: Predict the outcome of genetic crosses. (11.2) A. How do geneticists use the principles of probability to make predictions about inheritance? B. Explain the principle of independent assortment. 2.A. How do geneticists use the principles of probability to make predictions about inheritance? Probability • the fraction or percentage that describes the chance of an event taking place • probability = # of times an event is expected to happen # of opportunities for an event to happen • predicts what should happen mathematically, not what will happen (chance) • the larger the sample size (# of trials) the close expected and observed results should be 2.A. How do geneticists use the principles of probability to make predictions about inheritance? • flipping a coin, throwing a die, spinner activity • flipping 2 coins ½ x ½ = ¼ • throwing 2 dice: 1/6 X 1/6 = 1/36 • Occurring together = ¼ x 1/36 = 1/144 • product rule • probability of 2 or more independent events occurring together, is the product of their individual probabilities Terms: • dominant allele represented by capital letter (G) • recessive allele represented by lower case same letter (g) • homozygous (pure strain) - both alleles of pair are alike • GG - homozygous dominant • gg - homozygous recessive • heterozygous (hybrid) - two alleles of pair are different- Gg • genotype - genetic makeup of organism (alleles it possesses for a trait) Examples: GG, Gg, gg • phenotype - the physical appearance of an organism as a result of its genotype • genotypic ratio - ratio of genotypes appearing in offspring • phenotypic ratio - ratio of offspring's phenotypes 2.A. How do geneticists use the principles of probability to make predictions about inheritance? Predicting Results of Monohybrid Crosses • cross involving one pair of contrasting traits • Punnett square - diagram to predict probability that certain traits will be inherited by offspring P P Key: P = purple flower p = white flower p genotypic ratio phenotypic ratio p Monohybrid Problem #2 Key: B= black coat b = brown coat genotypic ratio phenotypic ratio Cross Bb x Bb Monohybrid Problem #3 Key: B= black coat b = brown coat genotypic ratio phenotypic ratio Cross Bb x bb Problem #4 How do you know if a black guinea pig is homozygous or heterozygous? • test cross • organism of unknown genotype is mated with a homozygous recessive organism 2.B. Explain the principle of independent assortment. Law of Independent Assortment • P1 yellow seed, round seed X green seed, wrinkled seed • F1 all yellow, round • F1 yellow, round X yellow, round (offspring F1) • F2: yellow, round green, wrinkled green, round yellow, wrinkled • factors for different characteristics are distributed to gametes independent of each other • dominant factors don't have to appear together nor do recessive • described by tetrads lining up randomly in metaphase I Dihybrid problems Predicting Results of Dihybrid Crosses • cross involving 2 pairs of contrasting traits Key: Parental Cross R= round seeds RRYY x rryy r = wrinkled seeds F1 Y = yellow seeds RrYy y = green seeds all round and yellow Dihybrid Problem RrYy x RrYy Possible gametes: Dihybrid Results Genotypic ratio: RRYY : RRYy : RRyy : RrYY : RrYy : Rryy : rrYY : rrYy: rryy Phenotypic ratio: Round Yellow :Round Green :Wrinkled Yellow :Wrinkled Green Standard #3 Determine how different factors can affect an organism’s traits. (11.3 & 14.1) A. Describe the patterns of inheritance of human traits. Give an example using a punnett square for each pattern: • Dominant vs. recessive, Incomplete dominance, Codominant, Multiple alleles, Polygenes, Sex linked, & X-chromosome in activated B. Explain how the environment plays a role in how genes determine traits. C. Explain how to use chi-square and how it relates to genetics? 3.A.Describe the patterns of inheritance of human traits. Human Single allele traits (more than 250) • can be due to autosomal recessive or dominant alleles • Dominant alleles • cleft chin, freckles, free earlobes, webbed fingers, Rh factor • Recessive alleles • PKU, sickle cell anemia, MC1R gene (Red hair) • PKU can’t make enzyme to break down amino acid, phenylalanine - it accumulates, destroys brain cells - severe mental retardation • genetic marker - short section of DNA that is known to have close association with particular gene nearby 3.A.Describe the patterns of inheritance of human traits. Incomplete dominance • two or more alleles influence phenotype, resulting in intermediate phenotype between dominant and recessive RW x RW Key: RR= red flowers WW = white flowers RW = pink flowers 3.A.Describe the patterns of inheritance of human traits. Codominance • neither allele dominant or recessive, nor do allele blend • both alleles expressed in heterozygous individual RR’ x RR’ KEY: RR = red coat R'R’ = white coat RR' = roan coat 3.A.Describe the patterns of inheritance of human traits. Multiple Alleles: • controlled by 3 or more alleles of same gene • blood type alleles - IA, IB, Ii • IA and IB are codominant when both expressed together and both are dominant to i genotype • phenotype type A type B type AB type O IAIA : I Ai IBIB: IBi I AIB ii Blood Type Problem I A IB x IBi genotypic ratio phenotypic ratio Blood Transfusions and Rh Factor Antibody: a protein produced to bind to an antigen, protects body from foreign substances (in plasma) Antigen: a protein that stimulates a response from the immune system (on the RBC’s) • Transfusions • concerned with antibodies of recipient • antibodies agglutinate (clump) antigens Type Antigens Antibodies Can receive from Can donate to A A b A,O A,AB B B a B,O B,AB AB A&B none A,B,AB,O AB O none a&b O A,B,AB,O Rh Factor • another antigen on RBC’s • 85% Rh + (have antigen) • 15% Rh - (no antigen) • Rh + blood given to Rh - person • Rh - person develops antibodies against Rh antigen • little problem on 1st transfusion but subsequent one could be fatal Erythroblastosis fetalis: (RBC) (destruction) (fetus) • mother Rh -, father Rh +, baby Rh + • 1st child (Rh +) • if any leakage across placenta to uterine blood vessels, mother will make antibodies against Rh antigen • antibodies not made fast enough to affect baby • subsequent child (Rh +) • antibodies already present will destroy baby’s RBC’s • can transfuse baby with Rh - blood in utero (dangerous) • Rhogam shot • given to mother within 72 hours of birth of child • destroys any Rh + blood antigens mother may have gotten from child (contains anti Rh antibodies) 3.A.Describe the patterns of inheritance of human traits. Polygenic traits • controlled by 2 or more genes • each gene has a small additive effect • continuous variation shown in the trait • • • • • • skin color eye color foot size Height Weight intelligence 3.A.Describe the patterns of inheritance of human traits. Sex linked: X-linked • A gene located on the sex chromosome • Sex linked genetic disorders • occur more in males • only one X chromosome • color-blindness, hemophilia, Duchenne muscular dystrophy • many other genes code for proteins needed for normal functions 3.B. Explain how the environment plays a role in how genes determine traits. • Environment can influence gene expression and influence genetically determined traits • An individuals phenotype is determined by • Genes • environment • Example: Western White Butterfly • Hatch in spring months- need more pigmentation to reach body temp needed for flight • Hatch in summer- need less pigmentation to avoid overheating 3.B. Explain how the environment plays a role in how genes determine traits. How the environment plays a role with human genes? • characters that are influenced strongly by environment and by genes • most complex traits are also polygenetic traits • skin color- expose to the sun causes the skin to become darker, no matter what the genotype is • Height- influenced by an unknown # of genes, but also a person’s nutrition and diseases • breast cancer, diabetes, heart disease, stroke, and schizophrenia Standard #4 Analyze how studying the human genome explains how traits are inherited (14.1). A. What is a karyotype? B. Identify the types of chromosomes in a karyotype. C. Analyze pedigree to determine traits. 4.A.What is a karyotype? Karyotype: • Shows a complete set of diploid chromosomes • Grouped in pairs • Arranged in order of decreasing size 4.B. Identify the types of chromosomes in a karyotype. • Autosome • any chromosome but the sex chromosomes • Sex Chromosomes • determine the sex of the organismin humans X and Y determine the sex in the offspring • XX= female • XY= male 4.C. Analyze pedigree to determine traits. Human Pedigrees • pedigree – • family record showing how trait is inherited over several generations (to find how traits are inherited) • show patterns of inheritance • carriers - have one recessive allele but don’t express it (can pass it on to offspring) http://www.youtube.com/watch?v=eYlJH81dSiw Standard #5 Explain causes of genetic disorders (14.2). A. Explain how small changes in DNA cause genetic disorders. Do genetic disorders have advantages? B. Summarize the problems caused by nondisjunction. C. Explain the how genetic disorders can be detected. 4.A. Explain how small changes in DNA cause genetic disorders. Small Changes: (review) • Sickle cell anemia• point mutation • substitution • Cystic fibrosis• frameshift mutation • deletion of 3 bases • Huntington’s disease • Dominant allele 4.A. Explain how small changes in DNA cause genetic disorders. Do genetic disorders have advantages? Sickle cell anemia: • People who are heterozygous • Are generally heathly • Highly resistant to malaria (claims 1 million lives a year) Cystic Fibrosis (CF) • People who are heterozygous • Protein produced by CF allele blocks the entry of typhoid bacterium (enter though digestive system) • People who live in city with poor sanitation and polluted water 4.B.Summarize the problems caused by nondisjunction. Nondisjunction disorders • monosomy - 45 chromosomes in zygote (one copy of a particular chromosome) • trisomy - 47 chromosomes in zygote (three copies of a particular chromosome) 4.B.Summarize the problems caused by nondisjunction. • Down syndrome • 47 chromosomes • trisomy #21 • both sexes • Turner syndrome – • 45 chromosomes (XO) • Only females • Klinefelter syndrome • 47 chromosomes (XXY) • Only males • Super female – • 47 chromosomes • trisomy of X • XXX • XYY (males) 4.C.Explain the how genetic disorders can be detected. Detecting Genetic Disorders • genetic screening for those with history of genetic disorders • karyotype, examine blood for presence or absence of certain proteins • genetic counseling • medical guidance informing them of potential problems for offspring • amniocentesis • some amniotic fluid removed at 14-16 weeks • analyze fetal cells and proteins, make karyotype 4.C.Explain the how genetic disorders can be detected. 4.C.Explain the how genetic disorders can be detected. • chorionic villi sampling – • sample of tissue between uterus and placenta at 8-10 weeks • villi same genetic makeup as embryo • make karyotype • genetic screening after birth for PKU • ultrasound – • sonogram (use sound waves) • fetoscopy – • view fetus, take picture