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W ARM -U P 1. Who was Mendel and how did he contribute to the process of science? 2. Draw a Punnett Square to show the following crosses: A. AA X aa B. Aa X aa C. Aa X Aa Definition List: Allele P generation F1 generation F2 generation Dominant Recessive Homozygous Heterozygous Phenotype Genotype
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W ARM -U P 1. What is a test cross? How is it used? 2. R = tongue roller, r = nonroller What would be the genotypic and phenotypic ratios for a cross between a heterozygous tongue roller and a non-roller? 3. Given: D = dimples, d = no dimples What traits would the children of 2 parents (Rrdd and rrDd) have? Definition List: Test cross Complete dominance Codominance Incomplete dominance Multiple alleles Polygenic traits Pedigree
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CH. 14 WARM-UP 1. Babies Jane (blood type B), John (blood type O), and Joe (blood type AB) were mixed up in the hospital. Who are their parents? Couple #1: A, A Couple #2: A,B Couple #3: B,O
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C H. 14 W ARM -U P 1. Cystic Fibrosis is an autosomal recessive disorder. What are the chances that 2 carriers for this disease will have a child with CF? 1. Huntington’s Disease is an autosomal dominant disorder. If a woman with this disease marries a normal man, what are the chances that their children will have the disease?
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W ARM -U P 1. What is a gene? 2. What is DNA made of? 3. What is Genetics?
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MENDEL AND GENETICS
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WHAT YOU NEED TO KNOW: Terms associated with genetics problems: P, F 1, F 2, dominant, recessive, homozygous, heterozygous, phenotype, genotype. How to derive the proper gametes when working a genetics problem. The difference between an allele and a gene. How to read a pedigree.
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G REGOR M ENDEL Austrian monk Brought experimental and quantitative approach to genetics Bred pea plants to study inhertance Why peas? Control mating (self- vs. cross- pollination) Many varieties available Short generation time
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Pollen transferred from white flower to stigma of purple flower anthers removed all purple flowers result M ENDEL ’ S WORK F1F1 P F2F2 self-pollinate Bred pea plants cross-pollinate true breeding parents (P) P = parental raised seed & then observed traits (F 1 ) F = filial (kids) allowed offspring to self-pollinate & observed next generation (F 2- grandkids )
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F 2 generation 3:1 75% purple-flower peas 25% white-flower peas L OOKING CLOSER AT M ENDEL ’ S WORK P 100% F 1 generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate Where did the white flowers go? White flowers came back!
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W HAT DID M ENDEL ’ S FINDINGS MEAN ? Traits come in alternative forms = alleles purple vs. white flower color 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
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P (parental) generation = true breeding plants F 1 (first filial) generation = offspring F 2 (second filial) generation = F 1 offspring
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W HAT DID M ENDEL ’ 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 Types of Allele dominant allele functional protein masks other alleles recessive allele allele makes a malfunctioning protein homologous chromosomes I’ll speak for both of us! wild type allele producing functional protein mutant allele producing malfunctioning protein
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MENDEL’S PRINCIPLES alleles 1. Alternate version of genes ( alleles ) cause variations in inherited characteristics among offspring. 2. For each trait, every organism inherits one allele from each parent. dominant recessive 3. If 2 alleles are different, the dominant allele will be fully expressed; the recessive allele will have no noticeable effect on offspring’s appearance. 4. Law of Segregation 4. Law of Segregation : the 2 alleles for each character separate during meiosis.
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Phenotype : expressed physical traits Genotype : genetic make-up of a trait
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Types of Genotypes dominant (P), recessive (p) homozygous = 2 same alleles (PP or pp) Homozygous Dominant Homozygous Recessive heterozygous = 2 different alleles (Pp)
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P UNNETT S QUARE Device for predicting offspring from a cross Example: Pp x Pp (P=purple, p=white) Genotypic Ratio: Phenotypic Ratio:
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Monohybrid cross : study 1 character eg. flower color Dihybrid cross : study 2 characters eg. flower color & seed shape
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Testcross: Testcross: H OW CAN WE TELL THE GENOTYPE OF AN INDIVIDUAL WITH THE DOMINANT PHENOTYPE ? T HE INDIVIDUAL COULD BE EITHER HOMOZYGOUS DOMINANT OR HETEROZYGOUS. T HE ANSWER IS TO CARRY OUT A TESTCROSS : BREEDING THE MYSTERY INDIVIDUAL WITH A HOMOZYGOUS RECESSIVE INDIVIDUAL I F ANY OFFSPRING DISPLAY THE RECESSIVE PHENOTYPE, THE MYSTERY PARENT MUST BE HETEROZYGOUS.
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Testcross:
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Law of Independent Assortment: Each pair of alleles segregates (separates) independently during gamete formation Strictly speaking, this law applies only to genes on different, non-homologous chromosomes. Genes located near each other on the same chromosome tend to be inherited together Eg. color is separate from shape
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D IHYBRID C ROSS Example: AaBb x AaBb
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P ROBABILITY Mendel’s laws of segregation and independent assortment reflect the rules of probability When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss Odds of getting tails on first coin flip: ½ or 50% Odds of getting tails on fifth coin flip after getting tails 4 times in a row: ½ or 50% The random assort alleles of each gene follow the same rules.
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T HE LAWS OF PROBABILITY GOVERN M ENDELIAN INHERITANCE Rule of Multiplication : The odds of two events occurring in a row can be calculated by multiplying their probabilities together. Ex. 1: probability of throwing 2 sixes 1/6 x 1/6 = 1/36 Ex. 2: probability of having 5 boys in a row ½ x ½ x ½ x ½ x ½ = 1/32 Ex. 3: If cross AABbCc x AaBbCc, probability of offspring with AaBbcc is: Answer: ½ x ½ x ¼ = 1/16
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T HE LAWS OF PROBABILITY GOVERN M ENDELIAN INHERITANCE Rule of Addition : The odds of getting a combination of events to occur can be calculated by adding their probabilities together. Ex. 1: If you flip two coins, your probabilities are:
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S EGREGATION OF ALLELES AND FERTILIZATION AS CHANCE EVENTS
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O THER INHERITANCE P ATTERNS The relationship between genotype and phenotype is rarely as simple as in the pea plant characters Mendel studied Many heritable characters are not determined by only one gene with two alleles However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance
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E XTENDING M ENDELIAN G ENETICS Inheritance of characters by a single gene may deviate from simple Mendelian patterns in the following situations: --When alleles are not completely dominant or recessive --When a gene has more than two alleles --When a gene produces multiple phenotypes
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E XTENDING M ENDELIAN G ENETICS Complete Dominance : heterozygote and homozygote for dominant allele are indistinguishable Eg. YY or Yy = Red Flower
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Incomplete Dominance : F 1 hybrids have appearance that is between that of 2 parents Eg. red x white = pink flowers
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Codominance : phenotype of both alleles is expressed Eg. Pink flower x White Flower.
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Multiple Alleles : gene has 2+ alleles Eg. human ABO blood groups Alleles = I A, I B, i I A,I B = Codominant
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B LOOD T YPING Phenotype (Blood Group) Genotype(s) Type AI A I A or I A i Type BI B I B or I B i Type ABIAIBIAIB Type Oii
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B LOOD T RANSFUSIONS Blood transfusions must match blood type Mixing of foreign blood clumping death Rh factor : protein found on RBC’s (Rh+ = has protein, Rh- = no protein)
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B LOOD T YPING P ROBLEM : A man who is heterozygous with type A blood marries a woman who is homozygous with type B blood. What possible blood types might their children have?
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Polygenic Inheritance: the effect of 2 or more genes acting upon a single phenotypic character (eg. skin color, height)
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Nature and Nurture: both genetic and environmental factors influence phenotype Hydrangea flowers vary in shade and intensity of color depending on acidity and aluminum content of the soil.
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Mendelian Inheritance in Humans Pedigree: diagram that shows the relationship between parents/offspring across 2+ generations Woman = Man = Trait expressed:
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P EDIGREE A NALYSIS
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G ENETIC D ISORDERS Cystic fibrosis (CF) Tay-Sachs disease Sickle-cell disease Phenylketonuria (PKU) Huntington’s disease (HD) Lethal dominant allele Autosomal Recessive Autosomal Dominant
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