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BIOLOGY Chapter 11: pp. 189 - 210 10th Edition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parents TT Ee tt Ee t T eggs E e Tt eggs Ee e T t T sperm EE Punnett square E spem Sylvia S. Mader Mendelian Patterns of Inheritance TT Tt Tt tt t Ee Offspring ee Offspring PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display 1 2 • 3.A.3: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. 3 Gregor Mendel • Austrian monk • University of Vienna • Conducted breeding experiments with the garden pea • Formulated fundamental laws of heredity in early 1860s • Had no knowledge of cells or chromosomes • Did not have a microscope 1. hybrid- offspring of 2 genetically different parents (tall w/short) YY 2. X yy = Yy phenotype- outward appearance of a char. (brown hair, yellow pea) 3. genotype- genetic make up of an organism (Tt, RR) Tt produces tall plant Tt is genotype tt produces short plant tt is genotype 4. homozygous- alleles in a pair are identical (TT, rr) Parents (P): TT x tt (tall & short) 5. heterozygous- alleles in a pair are different (Tt, Rr) Offspring (F1): Tt (all tall) 6. recessive- trait doesn’t show up unless both alleles are lower case letter. i.e. blue eyes, short plant 7. dominant- trait shows up as long as 1 of alleles is upper case letter. i.e. brown eyes, tall plant 8. co-dominant- both letters get to show. i.e. blood typing (i, IA, IB ) (IAIB = AB blood type) The Blood Blood Types- genetic alleles determine your blood type: IA, IB, or i. a. If you have IAIA or IAi, your blood type is A, IBIB or IBi is blood type B, ii is blood type O, and IAIB is AB. A B Antigens determine blood type. They stimulate an immune response. Body produces antibodies to combat antigens. (only for the other blood types however) Universal Donor? Universal Receiver? The Blood Rhesus factor (Rh factor)- Rh+ if you have Rh antigen on RBC. If Rh- mother is pregnant w/ Rh+ baby can complicate next pregnancy. 9. Punnett square- chart used to solve genetic problems, to predict genotypes and phenotypes (must know genotypes of parents) • Monohybrid cross- Looking at 1 trait. Sperm Cell Possibilities Egg Cell Possibilities T T t Tt Tt t Tt Tt Possible Offspring & Probability Mendel’s Monohybrid Crosses: An Example Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation TT P gametes tt T t F1 generation Tt F1 gametes T t F2 generation sperm T TT Tt Tt tt t Offspring Allele Key T = tall plant t = short plant Phenotypic Ratio 3 1 tall short 11 10. Incomplete Dominance- when 1 phenotype is not dominant over the other. Heterozygote shows a “blended” trait. 11. Sex-Linked Traits- traits on only the X or Y (sex) chromosome. (Hemophilia, colorblindness– both on the X chromosome) XY means male. X from mom. Y from dad. XX means female. X from mom. X from dad. Laws of Genetics 1. Law of unit factors- he deduced that there are units in the cell (now know them as genes) that determine the trait and they come in pairs (1 from each parent). Laws of Genetics 2. Law of segregation- gene pairs (alleles) are separated during gamete formation. Gametes have ½ # of chromosomes or alleles as parent has. Laws of Genetics 3. Law of dominance- one trait appears whenever an allele for that trait exists (dominant trait - uppercase) and one trait will only be exhibited if there are two alleles for it (recessive trait – lower case). • A test cross can be used to discover the genotype of a plant with a dominant trait. Example: tall plant, not sure if it is TT or Tt. Cross-pollinate w/ a homozygous recessive (tt) short plant. If all offspring are tall, then parent plant is TT. T ? T ? t t tall short t t tall short Laws of Genetics 4. Law of independent assortment- genes for different traits (flower color & height) are inherited independently of one another. If genotype is RrYy, R and r will separate from each other as well as from Y and y * Mendel’s experiments w/ dihybrid crosses (differ in 2 traits) led him to the last law. Dihybrid Crosses • Dihybrid cross • Predictions of crosses are based on probability (dividing # of desired outcomes by total # of outcomes) • i.e. 1 in 2 chance of flipping heads on a quarter YS Ys YS Ys yS ys Dihybrid Inheritance yS ys • Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans. • These are sex linked traits. • Click4Biology: theoretical genetics • Sex Linkage refers to genes that are on the X chromosome (which is larger than the Y chromosome). Females are more apt to avoid a recessive trait, since they have 2 X chromosomes. • Color blindness and hemophilia are sex linked traits. • Free biology Animations (the Romanovs) • Sex Linked Traits • Females can be homozygous or heterozygous with respect to sex-linked genes. • Female carriers are heterozygous for X-linked recessive alleles. • Colorblindness- Xe • Female not colorblind- XE XE ; XE Xe (carrier) • Female colorblind- Xe Xe • Male not colorblind- XE Y • Male colorblind- Xe Y *Males have 1 X therefore they will be colorblind if they get the recessive from their mother. If they get the dominant from mom they will not. *If the observed distribution is the same for M & F, then the trait is probably NOT sex-linked. If not then – Sex Linked. 25 X – Linked Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation XrY P gametes Xr XRXR XR Y F1 generation XRY XRXr eggs XR F1 gametes Xr F2 generation sperm XR XRXR XRXr XRY XrY Y Offspring Allele Key XR = red eyes Xr = white eyes Phenotypic Ratio females: males : 1 1 all red-eyed red-eyed white-eyed Distribution is different for M & F. Sex-linked? Autosomal? 26 Chi square test • F1 gen= Red eye Female (XRXr) x Red eye Male (XRY) • F2 gen (predicted)= Female-50 red eye; Male-25 red, 25 white • F2 gen (actual)= 51 red F; 26 red M; 23 white M • Ʃ (o-e)2/ e = (51-50)2 / 50 + (26-25)2 / 25 + (23-25)2 / 25 = 1/50 + 1/25 + 4/25 = 11/50= 0.22 df (# outcomes – 1)= 2 .05= 5.991 0.22 < 5.991, Accept null hypothesis! No statistical difference observed/expected! Chi-squared Test – YouTube 27 X-Linked Recessive Pedigree Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. XbY XBXB XBY XBXb daughter grandfather XBY XbXb XbY XBY XBXB XBXb Xb Y grandson XBXB XBXb XbXb XbY XbY Key = Unaffected female = Carrier female = Color-blind female = Unaffected male = Color-blind male X-Linked Recessive Disorders • More males than females are affected. • An affected son can have parents who have the normal phenotype. • For a female to have the characteristic, her father must also have it. Her mother must have it or be a carrier. • The characteristic often skips a generation from the grandfather to the grandson. • If a woman has the characteristic, all of her sons will have it. • 3.A.4: The inheritance pattern of many traits cannot be explained by simple Mendelian genetics. • 4.C.2: Environmental factors influence the expression of the genotype in an organism. • Pedigrees! 29 Human Genetic Disorders • Genetic disorders are medical conditions caused by alleles inherited from parents • Autosome - Any chromosome other than a sex chromosome (X or Y) • Genetic disorders caused by genes on autosomes are called autosomal disorders • Some genetic disorders are autosomal dominant • An individual with AA has the disorder • An individual with Aa has the disorder • An individual with aa does NOT have disorder • Other genetic disorders are autosomal recessive • An individual with AA does NOT have disorder • An individual with Aa does NOT have disorder, but is a carrier • An individual with aa DOES have the disorder • Mendelian Genetics 30 Autosomal Recessive Pedigree Chart Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. I II III IV aa A? A? Aa Aa Aa * Aa aa aa A? A? A? A? Key aa = affected Aa = carrier (unaffected) AA = unaffected A? = unaffected Autosomal recessive disorders (one allele unknown) • Most affected children have unaffected parents. • Heterozygotes (Aa) have an unaffected phenotype. • Two affected parents will always have affected children. • Close relatives who reproduce are more likely to have affected children. • Both males and females are affected with equal frequency. 31 Autosomal Dominant Pedigree Chart Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Aa Aa I * II III Aa aa Aa Aa aa A? aa aa aa aa aa aa Key AA = affected Aa = affected A? = affected (one allele unknown) aa = unaffected Autosomal dominant disorders • affected children will usually have an affected parent. • Heterozygotes (Aa) are affected. • Two affected parents can produce an unaffected child. • Two unaffected parents will not have affected children. • Both males and females are affected with equal frequency. 33 Autosomal Recessive Disorders • Tay-Sachs Disease • Progressive deterioration of psychomotor functions • Cystic Fibrosis • Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous • Phenylketonuria (PKU) • Lack enzyme for normal metabolism of phenylalanine 34 Cystic Fibrosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H2O Cl- Cl- ClCl- H2O H2O Cl- nebulizer defective channel percussion vest thick mucus © Pat Pendarvis 35 Methemoglobinemia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy Division of Medical Toxicology, University of Virginia 36 Autosomal Dominant Disorders • Neurofibromatosis • Tan or dark spots develop on skin and darken • Small, benign tumors may arise from fibrous nerve coverings • Huntington Disease • Neurological disorder • Progressive degeneration of brain cells • Severe muscle spasms • Personality disorders 37 A Victim of Huntington Disease Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. JK JJ JK JL JK JL KL a. JL JK JK JL JL JL JJ KL JJ KL KL b. a: © Steve Uzzell JJ KL JJ JK JK JK JK KL JK JK KL KK KL KL KL JL JJ 38 Pleioptropic Effects • Pleiotropy • A gene that affects more than one characteristic of an individual • Sickle-cell (incomplete dominance • Occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits. • Marfan syndrome have disproportionately long arms, legs, hands, and feet; a weakened aorta; poor eyesight 39 Marfan Syndrome Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Connective tissue defects Skeleton Heart and blood vessels Chest wall deformities Mitral valve Long, thin fingers, arms, legs prolapse Scoliosis (curvature of the spine) Flat feet Long, narrow face Loose joints Enlargement of aorta Eyes Lens dislocation Severe nearsightedness Aneurysm Aortic wall tear (Left): © AP/Wide World Photos; (Right): © Ed Reschke Lungs Collapsed lungs Skin Stretch marks in skin Recurrent hernias Dural ectasia: stretching of the membrane that holds spinal fluid 40 Polygenic Inheritance • Occurs when a trait is governed by two or more genes having different alleles Polygenetic Inheritance • Each dominant allele has a quantitative effect on the phenotype • These effects are additive • Result in continuous variation of phenotypes 41 Frequency Distributions in Polygenic Inheritance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. P generation Game genetics F1 generation F2 generation Proportion of Population 20 — 64 15 — 64 6 — 64 1 — 64 Genotype Examples 42 • Epistasis • A gene at one locus interferes with the expression of a gene at a different locus • Human skin color (polygenic inheritance) • 1 gene turns another gene on or off (albino mice) The “B” “b” gene determines mouse coat color. If there is “cc” present the gene “B” will be turned off and the mouse is white.