Genetics and the Work of Gregor Mendel Slide 2 Gregor Mendel Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas Used experimental design Used mathematical analysis Collected and counted peas Scientific method Slide 3 Where are genes located? On chromosomes! Remember chromosomes are made up of DNA located inside of the nucleus Every individual receives one copy of each gene from both parents Slide 4 Mendels Work Bred pea plants Cross-pollinated Raised seed and then observed traits Allowed offspring to self- pollinate and observed next generation. Slide 5 Mendel collected data for 7 traits Slide 6 Generations P1= parent generation F1= first generation after the parent generation F2 = second generation after the F1 generation (F1 hybrid is a term used in genetics and selective breeding. F1 stands for Filial 1, the first filial generation seeds/plants or animal offspring resulting from a cross mating of distinctly different parental types.) Slide 7 Slide 8 Mendels Peas in a nutshell P1 = TT (homozygous tall) x tt (homozygous short) Results= 100% Tt heterozygous tall plants (F1 generation) F2= Tt x Tt (he crossed two offspring from the F1 generation) Results= 25% TT, 50% Tt, 25% tt (F2 generation) Slide 9 Law of Segregation When Mendel performed cross-pollination between a true-breeding yellow pod plant and a true-breeding green pod plant, he noticed that all of the resulting offspring, F1 generation, were green. He then allowed all of the green F1 plants to self-pollinate. He referred to these offspring as the F2 generation. Mendel noticed a 3:1 ratio in pod color. About 3/4 of the F2 plants had green pods and about 1/4 had yellow pods. From these experiments Mendel formulated what is now known as Mendel's law of segregation. Slide 10 Law of Segregation Mendel's law of segregation states that allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. Egg T t Sperm The resulting union would be Tt. Slide 11 Law of Segregation four main ideas There are alternative forms for genes. For each characteristic or trait organisms inherit two alternative forms of that gene, one from each parent. These alternative forms of a gene are called alleles. (such as T = tall, t= short) When gametes (sex cells) are produced, allele pairs separate or segregate leaving them with a single allele for each trait. When the two alleles of a pair are different, one is dominant and the other is recessive. Slide 12 Law of Segregation From Mendel's law of segregation we see that the alleles for a trait separate when gametes are formed (through a type of cell division called meiosis). These allele pairs are then randomly united at fertilization. Traits come in these combinations: Homozygous= both letters are the SAME (TT, tt) Heterozygous = there is both a capital and lower case letter in the pair (Tt) Slide 13 Genotype vs. phenotype Difference between how an organism looks and its genes Phenotype what the organism looks like Genotype genetic makeup of the organism Explain cross using Mendels idea of .Dominant and recessive .Phenotype and genotype Slide 14 What did Mendels Findings mean? Some traits mask others Purple & white flowers are separate traits that do not blend Purple x white light purple Dominant allele LAW OF DOMINANCE Functional protein that masks another gene Affects the characteristic Recessive allele Not noticable effect Allele makes a non-functioning protein Slide 15 Warm UP Cross a homozygous white flower with heterozygous white flower. What is the probability of getting a purple flower? Slide 16 Making Crosses Alleles are represented as letters flower color alleles P (dominant) or p (recessive) True breeding purple flowers = PP True breeding white flowers = pp PP x pp Pp Slide 17 Mendels system is just TOO easy! Peas are genetically simple Most traits are controlled by a single gene Each gene only has 2 versions 1 completely dominant 1 recessive Slide 18 Many genes, one trait Polygenic inheritance Additive effects of many genes Humans Skin color Height Weight Eye color Intelligence behaviors Slide 19 Independent Assortment When more than one gene passes from generation to generation, each gene separates independently of the other Produces two factor crosses Yellow round peas x Green wrinkled peas RRYY x rryy Slide 20 Human Skin Color AaBbCc x AaBbCc Can produce a wide range of shades Most children = intermediate skin color Some can be very light, some can be very dark Slide 21 Human Skin Color Slide 22 Two Factor cross = dyhibrid cross Slide 23 Coat color in other animals Two genes: E, e and B, b Color = E; no color = e How dark the color is: B = black, b= brown Slide 24 Slide 25 Incomplete dominance Hybrids have an in-between appearance RR = red flowers rr = white flowers Rr = pink flowers Make 50 % less color Slide 26 Incomplete dominance Slide 27 Codominance Equal dominance Human blood ABO blood groups 3 versions A, B, i A & B alleles are codominant Both A & B alleles are dominant over the i allele The genes code for different sugars on the surface of red blood cells Name tag of the red blood cell Slide 28 Slide 29 A type A female would like to have a child with a Type B male. The type A females genotype is IAi. The type B male is IBIB. What are the possible genotypes and phenotypes for their child? What if the parents are Type O and Type AB? What are the possible genotypes and phenotypes for their child? Slide 30 Many genes, one trait Polygenic inheritance Additive effects of many genes Humans Skin color Height Weight Eye color Intelligence behaviors Slide 31 Independent Assortment When more than one gene passes from generation to generation, each gene separates independently of the other Produces two factor crosses Yellow round peas x Green wrinkled peas RRYY x rryy Slide 32 Human Skin Color AaBbCc x AaBbCc Can produce a wide range of shades Most children = intermediate skin color Some can be very light, some can be very dark Slide 33 Human Skin Color Slide 34 Two Factor cross = dyhibrid cross Slide 35 Coat color in other animals Two genes: E, e and B, b Color = E; no color = e How dark the color is: B = black, b= brown Slide 36 Slide 37 Environmental Effect Phenotype is controlled by both the environment and genes altering the pH of the soil = Blue flowers appear when the soil has an acidic pH of 5.5 or lower Slide 38 Coat color in Arctic animals is influenced by the environment.