Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Mendelian Genetics copyright cmassengale 1 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 2 *Gregor Mendel (1822-1884) Responsible for the Laws governing Inheritance of Traits copyright cmassengale 3 Gregor Johann Mendel Austrian monk Studied the inheritance of traits in pea plants Developed the laws of inheritance Mendel's work was not recognized until the turn of the 20th century copyright cmassengale 4 *Gregor Johann Mendel Called the “Father of Genetics" copyright cmassengale 5 Site of Gregor Mendel’s experimental garden in the Czech Republic copyright cmassengale 6 *Genetic Terminology Trait - any characteristic that can be passed from parent to offspring Heredity - passing of traits from parent to offspring Genetics - study of heredity copyright cmassengale 7 *Terminology Genotype - gene combination for a trait (e.g. RR, Rr, rr) Phenotype - the physical feature resulting from a genotype (e.g. red, white) copyright cmassengale 8 *Genotypes Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure Homozygous dominant = TT, RR, FF, GG Homozygous recessive = tt, rr, ff, gg, copyright cmassengale 9 *Homozygous dominant = TT, RR, FF, GG *Homozygous recessive = tt, rr, ff, gg, *Heterozygous genotype - also called hybrid Tt, Rr, Ff, Gg copyright cmassengale 10 *Heterozygous genotype gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid Tt, Rr, Ff, Gg copyright cmassengale 11 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 12 *Types of Genetic Crosses Monohybrid cross - cross involving a single trait e.g. flower color Dihybrid cross - cross involving two traits e.g. flower color & plant height Trihybrid Polyhybrid copyright cmassengale 13 *Punnett Square Used to help solve genetics problems copyright cmassengale 14 copyright cmassengale 15 *Designer “Genes” Alleles - two forms of a gene (dominant & recessive) Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) copyright cmassengale 16 Genotype & Phenotype in Flowers Genotype of alleles: R = red flower r = yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: Genotypes RR Rr rr Phenotypes RED RED YELLOW copyright cmassengale 17 *Genes and Environment Determine Characteristics copyright cmassengale 18 Mendel’s Pea Plant Experiments copyright cmassengale 19 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 20 Why peas, Pisum sativum? Can be grown in a small area Produce lots of offspring Produce pure plants when allowed to self-pollinate several generations Can be artificially cross-pollinated copyright cmassengale 21 Reproduction in Flowering Plants Pollen contains sperm Produced by the stamen Ovary contains eggs Found inside the flower Pollen carries sperm to the eggs for fertilization Self-fertilization can occur in the same flower Cross-fertilization can occur between flowers copyright cmassengale 22 Mendel’s Experimental Methods Mendel hand-pollinated flowers using a paintbrush He could snip the stamens to prevent self-pollination Covered each flower with a cloth bag He traced traits through the several generations copyright cmassengale 23 How Mendel Began Mendel produced pure strains by allowing the plants to selfpollinate for several generations copyright cmassengale 24 Eight Pea Plant Traits Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green (y) Pod Shape --- Smooth (S) or wrinkled (s) Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower color --- Purple (P) or white (p) copyright cmassengale 25 copyright cmassengale 26 copyright cmassengale 27 Mendel’s Experimental Results copyright cmassengale 28 Did the observed ratio match the theoretical ratio? The theoretical or expected ratio of plants producing round or wrinkled seeds is 3 round :1 wrinkled Mendel’s observed ratio was 2.96:1 The discrepancy is due to statistical error The larger the sample the more nearly the results approximate to the theoretical ratio copyright cmassengale 29 *Generation “Gap” Parental P1 Generation = the parental generation in a breeding experiment. F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) From breeding individuals from the P1 generation F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) From breeding individuals from the F1 generation copyright cmassengale 30 Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt copyright cmassengale 31 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 32 Monohybrid Crosses copyright cmassengale 33 P1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled seeds RR x rr r r R Rr Rr R Rr Rr Genotype: Rr Phenotype: Round Genotypic Ratio: All alike Phenotypic Ratio: All alike copyright cmassengale 34 P1 Monohybrid Cross Review Homozygous dominant x Homozygous recessive Offspring all Heterozygous (hybrids) Offspring called F1 generation Genotypic & Phenotypic ratio is ALL ALIKE copyright cmassengale 35 F1 Monohybrid Cross Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds Rr x Rr R r R RR Rr r Rr rr Genotype: RR, Rr, rr Phenotype: Round & wrinkled G.Ratio: 1:2:1 P.Ratio: 3:1 copyright cmassengale 36 F1 Monohybrid Cross Review Heterozygous x heterozygous Offspring: 25% Homozygous dominant RR 50% Heterozygous Rr 25% Homozygous Recessive rr Offspring called F2 generation Genotypic ratio is 1:2:1 Phenotypic Ratio is 3:1 copyright cmassengale 37 What Do the Peas Look Like? copyright cmassengale 38 …And Now the Test Cross Mendel then crossed a pure & a hybrid from his F2 generation This is known as an F2 or test cross There are two possible testcrosses: Homozygous dominant x Hybrid Homozygous recessive x Hybrid copyright cmassengale 39 *TEST CROSS – done to determine an unknown genotype of an organism that looks dominant. Cross with a (HR) homozygous recessive organism copyright cmassengale 40 F2 Monohybrid Cross st (1 ) Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds RR x Rr R r R RR Rr R RR Rr Genotype: RR, Rr Phenotype: Round Genotypic Ratio: 1:1 Phenotypic Ratio: All alike copyright cmassengale 41 F2 Monohybrid Cross (2nd) Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Wrinkled seeds x Round seeds rr x Rr R r r Rr Rr r rr rr Genotype: Rr, rr Phenotype: Round & Wrinkled G. Ratio: 1:1 P.Ratio: 1:1 copyright cmassengale 42 F2 Monohybrid Cross Review Homozygous x heterozygous(hybrid) Offspring: 50% Homozygous RR or rr 50% Heterozygous Rr Phenotypic Ratio is 1:1 Called Test Cross because the offspring have SAME genotype as parents copyright cmassengale 43 Practice Your Crosses Work the P1, F1, and both F2 Crosses for each of the other Seven Pea Plant Traits copyright cmassengale 44 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 45 Mendel’s Laws copyright cmassengale 46 SCI.9-12.B-4.6 -- Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). copyright cmassengale 47 *Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds) copyright cmassengale 48 Law of Dominance copyright cmassengale 49 *Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. copyright cmassengale 50 Applying the Law of Segregation copyright cmassengale 51 *Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. Not all of mom’s traits stay together. Mom’s and Dad’s traits are combined differently, copyright cmassengale 52 *Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2n (n = # of heterozygotes) copyright cmassengale 53 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 54 Question: How many gametes will be produced for the following allele arrangements? Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd 3. MmNnOoPPQQRrssTtQq copyright cmassengale 55 Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCD 3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes copyright cmassengale 56 Dihybrid Cross Traits: Seed shape & Seed color Alleles: R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations copyright cmassengale 57 Dihybrid Cross RY Ry rY ry RY Ry rY ry copyright cmassengale 58 Dihybrid Cross RY RY RRYY Ry RRYy rY RrYY ry RrYy Ry rY ry RRYy RrYY RrYy RRyy RrYy Rryy RrYy rrYY rrYy Rryy rrYy rryy copyright cmassengale Round/Yellow: Round/green: 9 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 phenotypic ratio 59 Dihybrid Cross Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 9:3:3:1 copyright cmassengale 60 Test Cross A mating between an individual of unknown genotype and a homozygous recessive individual. Example: bbC__ x bbcc BB = brown eyes Bb = brown eyes bb = blue eyes CC = curly hair Cc = curly hair cc = straight hair bC b___ bc copyright cmassengale 61 Test Cross Possible results: bc bC b___ C bbCc bbCc or bc copyright cmassengale bC b___ c bbCc bbcc 62 Summary of Mendel’s laws LAW DOMINANCE SEGREGATION INDEPENDENT ASSORTMENT PARENT CROSS OFFSPRING TT x tt tall x short 100% Tt tall Tt x Tt tall x tall 75% tall 25% short RrGg x RrGg round & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods copyright cmassengale 63 Incomplete Dominance and Codominance copyright cmassengale 64 *Incomplete Dominance F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white (rr) r r RR = red flower rr = white flower R R copyright cmassengale 65 Incomplete Dominance r r R Rr Rr R Rr Rr produces the F1 generation All Rr = pink (heterozygous pink) copyright cmassengale 66 Incomplete Dominance copyright cmassengale 67 *Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type 1. 2. 3. 4. type type type type A B AB O = = = = IAIA or IAi IBIB or IBi IAIB ii copyright cmassengale 68 Codominance Problem Example: homozygous male Type B (IBIB) x heterozygous female Type A (IAi) IA i IB IAIB IBi IB IAIB IBi copyright cmassengale 1/2 = IAIB 1/2 = IBi 69 Another Codominance Problem • Example: male Type O (ii) x female type AB (IAIB) IA IB i IAi IBi i IAi IBi copyright cmassengale 1/2 = IAi 1/2 = IBi 70 *Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) AB (IAIB) X copyright cmassengale girl - type 71 Codominance Answer: IA IB i i IAIB ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale 72 copyright cmassengale 73 *Sex-linked Traits Traits (genes) located on the sex chromosomes Sex chromosomes are X and Y XX genotype for females XY genotype for males Many sex-linked traits carried on X chromosome copyright cmassengale 74 *Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye color XX chromosome - female Xy chromosome - male copyright cmassengale 75 Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) XRY x XrXr Remember: the Y chromosome in males does not carry traits. Xr Xr RR = red eyed Rr = red eyed R X rr = white eyed XY = male Y XX = female copyright cmassengale 76 Sex-linked Trait Solution: Xr XR XR Xr Y Xr Y Xr XR Xr Xr Y 50% red eyed female 50% white eyed male copyright cmassengale 77 *Female Carriers copyright cmassengale 78 *Examples of human sex-linked traits and disorders Hemophilia – missing a protein necessary for normal blood clotting Duchenne Muscular dystrophy – doesn’t have the right protein for muscles (muscle degeneration, trouble walking and breathing, early death) Red-Green Colorblindness – cannot tell the difference between red and green – see as shades of gray copyright cmassengale 79 A woman who is a carrier for Duchenne muscular dystrophy marries a man who is normal. a. what are the chances they will have a child that is a carrier? ________ b. what are the chances they will have a child that has the disorder? _______ c. what are the chances they will have a child that is totally normal? ________ d. They have a boy. What are the chances he has the disorder? ________ e. They have a girl. What are the chances she has the disorder?_________ copyright cmassengale 80 Color blindness is sometimes acquired. Chronic illnesses that can lead to color blindness include Alzheimer's disease, diabetes mellitus, glaucoma, leukemia, liver disease, chronic alcoholism, macular degeneration, multiple sclerosis, Parkinson's disease, sickle cell anemia , and retinitis pigmentosa. Accidents or strokes that damage the retina or affect particular areas of the brain eye can lead to color blindness. Some medications such as antibiotics , barbiturates, anti-tuberculosis drugs, high blood pressure medications, and several medications used to treat nervous disorders and psychological problems may cause color blindness. Industrial or environmental chemicals such as carbon monoxide, carbon disulfide, fertilizers, styrene, and some containing lead can cause loss of color vision. Occasionally, changes can occur in the affected person's capacity to see colors after age 60. http://www.encyclopedia.com/topic/color_blindness.aspx SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 82 Epistasis – When the presence of a gene in one location prevents the expression of a trait somewhere else Penetrance – The percent of the population that has the gene and expresses it. Tay Sachs has 100% penetrance. Retinoblastoma has 90% Expressivity – The degree to which a trait is expressed in an individual. copyright cmassengale 83 *Types of mutations Somatic cells = body cells Germ cells = gametes 1. Deletion 2. Addition 3. Inversion 4. Translocation copyright cmassengale 84 *Human Genetic Diseases and Disorders Sickle Cell Anemia – When the RBC changes shape because of a mutation. Causes blood clots and damages organs. More common in African-Americans Cystic Fibrosis – a transport protein is missing in the lungs and a thick mucus develops that clogs lungs and organs common in whites copyright cmassengale 85 *Tay Sachs – An enzyme is missing to break dawn fats in the brain. Brain cells are killed – always fatal. More common in Jews PKU – phenylketonuria cannot break down a specific amino acid, can lead to brain damage, seizures and mental retardation. copyright cmassengale 86 *Marfan syndrome – taller than average, longer wing span than height – has weakened heart valves and aorta. Can lead to sudden death copyright cmassengale 87 Genetic Practice Problems copyright cmassengale 88 Breed the P1 generation tall (TT) x dwarf (tt) pea plants t t T T copyright cmassengale 89 SCI.9-12.B-4.6 - - Predict inherited traits by using the principles of Mendelian genetics (including segregation, independent assortment, and dominance). SCI.9-12.B-4.7 -- Summarize the chromosome theory of inheritance and relate that theory to Gregor Mendel's principles of genetics. copyright cmassengale 90 Solution: tall (TT) vs. dwarf (tt) pea plants t t T Tt Tt produces the F1 generation T Tt Tt All Tt = tall (heterozygous tall) copyright cmassengale 91 Breed the F1 generation tall (Tt) vs. tall (Tt) pea plants T t T t copyright cmassengale 92 Solution: tall (Tt) x tall (Tt) pea plants T t T TT Tt t Tt tt produces the F2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype copyright cmassengale 93 Pedigrees are used to show the history of inherited traits through a family. In a pedigree, males are represented by squares and females by circles . An individual who exhibits the trait in question, for example, someone who suffers from hemophilia, is represented by a filled symbol or . A horizontal line between two symbols represents a mating . The offspring are connected to each other by a horizontal line above the symbols and to the parents by vertical lines. Roman numerals (I, II, III, etc.) symbolize generations. Arabic numerals (1,2,3, etc.) symbolize birth order within each generation. In this way, any individual within the pedigree can be identified by the combination of two numbers (i.e., individual II3). copyright cmassengale 94 *Pedigrees – a diagram to show a trait in a family Males = Females = Shaded circles or squares mean an individual has the trait. Half shaded means they are a carrier copyright cmassengale 95 copyright cmassengale 96 copyright cmassengale 97 copyright cmassengale 98