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Ch. 14 Mendel and the Gene Idea Nov 1 6:30 PM 1 Essential Question: How do genes affect inheritance? Nov 1 6:32 PM 2 Gregor Mendel = Father of Genetics 18221884 1843 entered monastery failed teacher exam studied under other scientists (Doppler and Unger), importance of math and science 1857 started breeding peas Nov 1 6:31 PM 3 Why peas??? easy to grow fast growing have many varieties could easily control cross fertilization normally self pollinators stamen and carpels are in same flower had easy traits to study character = heritable feature ex. flower color trait = variant for a character ex. purple or white color flower Nov 1 6:42 PM 4 Traits Mendel chose to study: seed color (yellow vs. green) seed shape (round vs. wrinkled) seed coat color (gray vs. white) pod shape (smooth vs. constricted) pod color (green vs. yellow) flower position (axial vs. terminal) plant height (tall vs. short) flower color (purple vs. white) chose traits that had no intermediates Nov 1 6:49 PM 5 How did he conduct his experiments? used true breeding plants = if allowed to self pollinate, would only produce offspring identical to themselves cut the immature stamen out and cross fertilized pea plants using a paint brush crossed two contrasting plants = hybridization Nov 1 6:54 PM 6 parent plants are called P generation hybrid offspring called F generation 1 (Filius/Filia) F generation crossed 1 with another F generation 1 = F generation 2 Nov 1 6:47 PM 7 Mendel's studies revealed two principles of heredity 1. Law of Segregation based on four concepts: a. alternative versions of genes (called alleles) account for variations in inherited characters alleles are DNA variations Nov 1 7:07 PM 8 b. for each character, an organism inherits two alleles, one from 1 from each parent if true breeding alleles are same if hybrids alleles are different c. if the two alleles at a locus differ, then one is dominant (determines organism's appearance), the other is recessive (no effect on appearance) Nov 1 7:15 PM 9 d. Law of segregation the two alleles for a heritable character separate during gamete formation and end up in different gametes (think meiosis!) sperm or egg only one of two alleles from somatic cell Nov 1 7:22 PM 10 Law of Segregation Nov 29:42 AM 11 Nov 29:40 AM 12 Round and wrinkled peas in same pod Nov 29:41 AM 13 Punnett Squares = diagrams used to predict allele composition of offspring Nov 1 7:39 PM 14 Terminology relating to genetics homozygous = identical alleles for a character can be dominant or recessive heterozygous= two different alleles for a gene not true breeders phenotype = physiological/appearance traits genotype = genetic makeup Nov 1 7:31 PM 15 Genotype vs. phenotype Nov 29:45 AM 16 How can we tell if a plant is a true breeder or a hybrid? do a testcross cross pollinate the plant with a homozygous recessive Nov 1 7:36 PM 17 2. Law of Independent Assortment Each pair of alleles segregates independently of other pairs of alleles during gamete formation (think meiosis!) figured this out by following two characters dihybrid plants Nov 1 7:42 PM 18 to test law of Independent assortment Nov 29:47 AM 19 Dihybrid Crosses Nov 1 7:46 PM 20 the law of segregation and the law of independent assortment reflect the probability of offspring Rules of Probability if event is absolutely certain to happen probability = 1 if event is certain not to happen, probability = 0 otherwise, probability is between 0 and 1 Nov 1 7:47 PM 21 to determine the possibility of two events happening ex. tossing two coins, each is independent of the other What is probability that both will be heads? 1/2 x 1/2 = 1/4 for monohybrid crosses: if heterozygote (Tt) crossed with heterozygote (Tt), what is the probability of TT? 1/2 x 1/2 = 1/4 Nov 1 8:01 PM 22 Probability of getting two heads with two coins Nov 29:49 AM 23 called the rule of multiplication *usually used when the word "and" is involved ex. What would the probability be of a child having blue eyes and blond hair? Nov 1 8:09 PM 24 Rule of Addition probability that an event will happen in two or more different ways ex. in a dihybrid cross of heterozygous F 1 generation (SsYy) S= spherical, s = wrinkled Y = yellow, y = green probability offspring are spherical = 3/4 (do monohybrid cross of Ss x Ss) 1/4 SS + 1/2 Ss = 3/4 Nov 1 8:12 PM 25 probability offspring are yellow = 3/4 (do monohybrid cross of Yy x Yy) 1/4 YY + 1/2 Yy = 3/4 To figure out probability of spherical and yellow: 3/4 x 3/4 = 9/16 (multiplication rule) Nov 58:34 AM 26 rule of addition usually uses the word "or" ex. What would be the possibility of having a blue eyed or green eyed child? 1/4 + 1/4 *key to using these rule is that alleles segregate independently so can look at them separately Nov 1 8:28 PM 27 Probability problems: What is the probability of each of the following pairs of parents will produce the indicated offspring? a. AABBCC x aabbcc AaBbCc b. AABbCc x AaBbCc AAbbCC c. AaBbCc x AaBbCc AaBbCc d. aaBbCC x AABbcc AaBbCc Nov 1 8:32 PM 28 What fraction of offspring from the cross PpYyRr x Ppyyrr would be predicted to exhibit recessive phenotypes for at least two of three characters? P = purple flowers p = white flowers Y = yellow seeds y = green seeds R = round seeds r = wrinkled seeds Nov 1 8:41 PM 29 Inheritance patterns can be more complex than what Mendel studied 1. Complete dominance one allele dominates over another, phenotypes of heterozygous and homozygous dominant are the same 2. Codominance two alleles affect the phenotype in separate ways ex. blood type AB both A and B are dominant Nov 1 8:52 PM 30 3. Incomplete dominance phenotype is in between both parent phenotypes ex. red snapdragons crossed with white snapdragons = pink snapdragons *keep in mind that dominance refers to the ability to produce something (synthesis of something like an enzyme), recessive = defect in production of enzyme heterozygous individuals produce equal amounts of normal and dysfunctional enzymes Nov 1 8:58 PM 31 incomplete Dominance in snapdragons Nov 29:52 AM 32 Nov 29:53 AM 33 TaySachs Disease cause recessive allele unable to metabolize lipids due to missing enz., causes seizures, blindness, motor/mental problems have disease if have two recessives no disease if heterozygote Nov 1 9:03 PM 34 Other conditions caused by dominant alleles polydactyly (extra fingers or toes) tongue rolling http://www.und.nodak.edu/dept/biology/introlab/bio100/tongue.jpg http://www.chkd.org/Images/CSSG/plasticsurgery/polydactyly2.jpg http://www.midwestrocklobster.com/cultbucket/hand6.gif Feb 127:21 AM 35 Multiple Alleles for a single gene ex. ABO blood types Four types A,B, AB, O based on enzymes that adds a carbohydrate to a red blood cell A I allele codes for enzyme that adds A carbohydrate *critical for blood transfusions Nov 1 9:09 PM 36 Multiple Alleles Nov 29:53 AM 37 ABO Blood Types Nov 29:54 AM 38 Pleiotropygenes that have multiple phenotypic effects ex. in Siamese cats light body with dark extremities and crossed eyes http://www.cfainc.org/breeds/profiles/siamese.html Nov 1 9:16 PM 39 Situations of two or more genes 1. Epistasis gene at one location affects phenotypic expression of gene at a second location ex. black fur (B) is dominant over brown fur (b) for mouse to be brown = bb second gene determines whether pigment will be deposited in hair (C = dominant) if mouse is cc, then coat is white no matter what other genotype is so, the gene for pigment deposition is epistatic to the gene coding for black or brown pigment Nov 1 9:20 PM 40 Epistasis Nov 29:59 AM 41 2. Polygenic Inheritance an additive effect of 2 or more genes on a single phenotype character ex. skin coloration (3 or more genes) height polygenic skin color Nov 1 9:26 PM 42 Can the environment affect gene expression? Yes! ex. nutrition differences, exercise most genes have a phenotypic range called a "norm of reaction" Nov 1 9:28 PM 43 How are human traits affected by inheritance? can understand them by looking at a pedigree = a diagram of a family tree showing heritable characters over many generations *helps us predict future probability of inheriting a trait Nov 1 9:31 PM 44 Pedigrees dominant trait Recessive trait Nov 210:02 AM 45 Recessive disorders: homozygous recessive to have the disorder if heterozygous = carrier (does not have disorder but could potentially give it to offspring) ex if both parents = heterozygous 1/4 chance of getting disorder 2/3 will of possible 3 "normals" will be carriers) Nov 1 9:37 PM 46 Cystic Fibrosis normal allele codes for protein that helps chloride transport between cells and extracellular fluid if missing protein no chloride channels causes thick and sticky mucus in lungs and digestive system leads to poor nutrient absorption, chronic bronchitis, bacterial infections lethal, die in 20's or 30's Nov 1 9:45 PM 47 Sickle cell diseaseblood disorder in African Americans (1 in 400) cause 1 amino acid change in hemoglobin protein if oxygen is low red blood cells form sickle shape, clog blood vessels heterozygotes healthy, but could suffer if oxygen is low advantage resistant to malaria Nov 1 9:49 PM 48 Sickle cell Nov 210:03 AM 49 Probability of passing on a disease causing trait increases the closer related you are why we don't marry first cousins!! Nov 1 9:54 PM 50 Dominant Inherited disorders Achondroplasia form of dwarfism (1 in 25,000) homozygous dominant and heterozygous are dwarfs 99.99% of people are homozygous recessive dominant disorders causing lethal disease are less common than recessive disorders Nov 1 9:56 PM 51 Huntington's Disease degenerative nervous system disease does not affect person until 3545 years old already may have passed it to offspring before a person knows if they have it if one parent has the allele 50% chance child will (1 in 10,000) can now test to see if have allele Nov 1 10:01 PM 52 pedigree of Huntington's Disease Nov 210:04 AM 53 Multifactorial Disorders genetic component plus environmental influence Ex. heart disease, diabetes, cancer, alcoholism, mental illness Nov 1 10:05 PM 54 How can we prevent the risk of getting a genetic disorder? genetic counseling (determining probabilities) testing ethical problems fetal testing amniocentesis chorionic villus sampling imaging techniques ultrasound newborn screening ex. PKU Nov 1 10:07 PM 55 Nov 210:05 AM 56 Nov 58:39 AM 57