Introduction to Genetics PDF

Chapter 12.1-12.3: Introduction to Genetics Gregor Mendel Austrian monk & scientist ○ “Father of Genetics” ○ Pea plants Small Easy to grow Hundreds of offspring Genetics - the study of heredity (how genes get passed down from one generation to the next. Mendel’s Experiments Character – heritable fea...

Chapter 12.1-12.3: Introduction to Genetics Gregor Mendel Austrian monk & scientist ○ “Father of Genetics” ○ Pea plants Small Easy to grow Hundreds of offspring Genetics - the study of heredity (how genes get passed down from one generation to the next. Mendel’s Experiments Character – heritable feature that varies among individuals ○ Ex: Flower color, seed shape Trait – Each variant for a character ○ Ex: Purple or white flowers / round or wrinkled seed Mendel’s Experiments Mendel’s Model Four main points: 1. Principle of Segregation - the two alleles for a trait separate during gamete formation (meiosis) ○ ○ 2. Alternative versions of genes account for variations in inherited traits Alleles – alternative versions of a gene For each traits, an organism inherits two copies of a gene, one from each parent Mendel’s Model 3. Principle of Dominance: If the two alleles at a locus differ, then the dominant allele determines appearance, while the recessive allele has no noticeable effect 4. Law of Segregation – two alleles for a heritable character segregate during gamete formation and end up in different gametes Processing Time: According to Mendel's principles, how are alleles for a trait inherited? What is the process called in Mendel's principle where alleles separate from each other during gamete formation? a. Crossing over b. Gene expression a. The organism inherits two copies of a gene, one from each parent. c. Mutation b. They are inherited only from the father According to Mendel's principle, how are different traits inherited? c. They are inherited only from the mother d. They are randomly inherited from any ancestor d. Segregation a. They are inherited independently b. They are always inherited together c. They are inherited in predetermined combinations d. They are randomly inherited without any relation Probability Probability scale ranges from 0-1 ○ Event certain to occur has a probability of 1 ○ Event certain not to occur has a probability of 0 With a coin, chance of flipping heads is ½ Every coin toss is an independent event ○ Probability does not change Probability Multiplication Rule ○ Probability of two or more independent events occurring together can be determined by multiplying their individual probabilities Addition Rule ○ Probability of any one of two or more mutually exclusive events occurring determined by adding their individual probabilities Processing Time: What is the probability of getting a head in a coin flip? What the probability of having a girl child? What the probability of getting a 3 on a roll of the dice? What the probability of having three girl children in a row? What the probability of getting a heads or a tails on a coin flip? Representation of Genes and Alleles 1. Alleles are represented by letters. 2. Capital = dominant allele T = tall Lowercase = recessive allele t = short 3. 1 gene = 2 alleles (1 from each parent) = 2 letters possible allele combos: TT, Tt, tt Genetic Vocabulary Heterozygous – two different alleles for a gene (Tt) Homozygous – pair of identical alleles for a gene (TT or tt) Genotype – genetic makeup (TT, Tt, or tt) Phenotype – appearance or observable traits (Tall or short) Let’s Practice: Using the characteristics of curly hair where curly is dominate (R) and straight is recessive (r), complete the chart below. Genotype Homozygous Dominant Homozygous Recessive Heterozygous Dominant Phenotype Traits Dominant allele Hair length Long or short Seed coat Gray or white Recessive allele l G Genes (genotype) Homozygous recessive Heterozygous dominant Coat pattern Tabby or stripeless Heterozygous dominant Leaf pattern Variegated or solid Homozygous dominant Tt V Appearance (phenotype) sdf Cross a heterozygous tall pea plant with a short pea plant (T= tall allele, t= short allele) Genotype Ratio Phenotype Ratio Practice Problem Having dimples is dominant over the absence of dimples. Cross a heterozygous dimpled man with a woman who does not have dimples. Show all work in the Punnett square and summarize your findings in the table. What is the genotype of the man? What is the genotype of the woman? Normal skin is dominant over albino skin. A woman who has normal skin, but whose father was albino, marries a heterozygous, normal skinned man. What type of offspring might they expect? Practice Problem What is the genotype of the woman? What is the genotype of the man? Dihybrid Cross: a cross that shows the possible offspring for two traits Fur Color: B: Black b: White Coat Texture: R: Rough r: smooth In this example, we will cross a heterozygous individual with another heterozygous individual. Their genotypes will be: BbRr x BbRr Dihybrid Cross: BbRr x BbRr First, you must find ALL possible gametes that can be made from each parent. Remember, each gamete must have one B and one R. FOIL (first, outside, inside, last) Write the gametes here: ________ ________ _________ _________ Dihybrid Crosses: a cross that shows the possible offspring for two traits BbRr x BbRr BR Fur Color: B: Black b: White BR Coat Texture: R: Rough r: Smooth Br Then, find the possible genotypes of the offspring bR br Br bR br How many of the offspring would have a black, rough coat? How many of the offspring would have a black, smooth coat? How many of the offspring would have a white, rough coat? How many of the offspring would have a white, smooth coat? BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth Use the following Punnett square to illustrate Mendel’s experiments True-breeding Round and Yellow (RRYY) x True-breeding wrinkled and green (rryy) True breeding Round, yellow seed (RRYY) True breeding Wrinkled, green seed (rryy) Right handedness (R) is dominant over left handedness (r). The ability to roll your tongue (T) is dominant over the inability to roll your tongue (t). What offspring might be expected from a cross involving the following parents: RRtt x RRTt Practice Problem Exception to Mendel's Rules 1. Some alleles are neither dominant nor recessive. 2. The majority of genes have more than 2 alleles. 3. Some traits are controlled by more than one gene. Incomplete Dominance One allele is not completely dominant over the other Blend + ing = Blending What type of offspring might be produced by two pink flowering plants? What are the genotypes of the parents? Practice Problem e c i t c a Pr m e l b o r P In a certain plant, flower color shows incomplete dominance, but the stem length shows dominance. The allele for long stem is dominant over the allele for short stem. Cross a heterozygous long-stemmed red plant with a short-stemmed pink plant. What is the genotype of the first parent? What is the genotype of the second parent? Codominance Phenotypes of both alleles clearly expressed Red and white camellia flower colors are codominant. What would be the result of a red flower crossing with a white flower? What are the genotypes of the parents? Practice Problem Multiple Alleles Three or more possible alleles for a trait ○ Ex: ABO blood types What types of offspring might be expected if one parent has type AB blood and the other parent is heterozygous for type A blood? What is the genotype of the first parent? What is the genotype of the second parent? Practice Problem Sex-Linked Inheritance Genes located on sex chromosomes Most often on X chromosome, but can be on Y chromosome. Practice Problem A normal man marries a heterozygous women for colorblindness. What are the chance of colorblindness in their son? What about their daughters? What is the genotype of the woman? What is the genotype of the man? Practice Problem A normal woman, whose father had hemophilia, married a normal man. What is the chance of hemophilia in their children? What is the genotype of the woman’s father? What is the genotype of the woman? What is the genotype of the man? Pedigrees: Let’s practice: 1. Which members of the family above are affected by Huntington’s Disease? 2. There are no carriers for Huntington’s Disease- you either have it or you don’t. With this in mind, is Huntington’s disease caused by a dominant or recessive trait? 3. How many children did individuals I-1 and I-2 have? 4. How many girls did II-1 and II-2 have? 5. How are individuals III-2 and II-4 related? Environment & Gene Expression Expression of a genotype can be affected by environmental influences, resulting in a range of phenotypes