Transcript Ch 9 PPT
Chapter 9 Fundamentals of Genetics Table of Contents Section 1 Mendel’s Legacy Section 2 Genetic Crosses I. Principles of Genetics A. HEREDITY B. Origin of Genetic C. Mendel’s Experiment D. Mendel’s Results a. Dominant b. Recessive E. Mendel’s Hypothesis a. Gene Segregation b. Punnett Squares F. Terminology a. Allele b. Genotype c. Phenotype d. Homozygous e. Heterozygous G. Simple Monohybrid Crosses H. Dihybrid Cross : Principle of Independent Assortment Chapter 9 Section 1 Mendel’s Legacy Objectives • Describe how Mendel was able to control how his pea plants were pollinated. • Describe the steps in Mendel’s experiments on true-breeding garden peas. • Distinguish between dominant and recessive traits. • State two laws of heredity that were developed from Mendel’s work. • Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes. Chapter 9 Section 1 Mendel’s Legacy Gregor Mendel • The study of how characteristics are transmitted from parents to offspring is called genetics. • Personal Information • Mendel’s Garden Peas – Mendel observed characteristics of pea plants. – Traits are genetically determined variants of a characteristic (like hair color or eye color). – Each characteristic occurred in two contrasting traits (one from each parent). Chapter 9 Section 1 Mendel’s Legacy Gregor Mendel, continued • Mendel’s Methods – Mendel used cross-pollination techniques in which pollen is transferred between flowers of two different plants. • Mendel bred plants for several generations that were truebreeding for specific traits and called these the P generation. • Offspring of the P generation were called the F1 generation. • Offspring of the F1 generation were called the F2 generation. Chapter 9 Section 1 Mendel’s Legacy Three Steps of Mendel’s Experiments Chapter 9 Section 1 Mendel’s Legacy Mendel’s Results and Conclusions • Recessive and Dominant Traits – Mendel concluded that inherited characteristics are controlled by two factors that occur in pairs. • dominant - trait that masked the other, like Purple. • recessive - trait that was masked, like white • The Law of Segregation – States that a pair of factors is segregated, or separated, during the formation of gametes. (remember homologous chromosomes separate) Chapter 9 Section 1 Mendel’s Legacy Mendel’s Results and Conclusions, continued • The Law of Independent Assortment – The law of independent assortment states that factors for individual characteristics are distributed to gametes independent of one another. – The law of independent assortment is observed only for genes that are located on different chromosomes (remember the homologous chromosomes line up is random and crossing over can occur) Chapter 9 Section 1 Mendel’s Legacy Support for Mendel’s Conclusions • Mendel’s factors are called alleles, or alternative forms of a gene. • One allele for each trait is passed from each parent to the offspring. – TRAIT or GENE = Color of flower – ALLELES = purple and white Chapter 9 Fundamentals of Genetics Table of Contents Section 1 Mendel’s Legacy Section 2 Genetic Crosses Chapter 9 Section 2 Genetic Crosses Objectives • Differentiate between the genotype and the phenotype of an organism. • Explain how probability is used to predict the results of genetic crosses. • Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses. • Explain how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait. • Differentiate a monohybrid cross from a dihybrid cross. Chapter 9 Section 2 Genetic Crosses Genetic TERMS The phenotype is the appearance of an organism, like purple or white The genotype is the genetic makeup of an organism, the alleles. • Heterozygous – two different alleles (Pp) • Homozygous – two alleles are the same (dominant – PP or recessive - pp). Chapter 9 Section 2 Genetic Crosses Probability • Probability is the likelihood that a specific event will occur. • A probability may be expressed as a decimal, a percentage, or a fraction. • A Punnett square can be used to predict the outcome of genetic crosses. • A cross in which one characteristic is tracked is a monohybrid cross. Chapter 9 Section 2 Genetic Crosses Monohybrid Cross of Heterozygous Plants In rabbits the allele for black coat color (B) is dominant over the allele for brown coat color (b). What is the genotypic ratio and phenotypic ratio be for a cross between a homozygous black rabbit and homozygous brown rabbit? White (W) hair in sheep is caused by the dominant gene while black (w) hair is recessive. A heterozygous white male and a black female are parents of a black lamb. What is the probability that their next lamb will be white? What are the genotypic and phenotypic ratios? In humans, polydactyly (an extra finger on each hand or toe on each foot) is due to a dominant gene. When one parent is polydactylous, but heterozygous, and the other parent is normal, what are the genotypic and phenotypic ratios of their children? Chapter 9 Section 2 Genetic Crosses Predicting Results of Monohybrid Crosses, continued • A testcross, in which an individual of unknown genotype is crossed with a homozygous recessive individual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait. Chapter 9 Section 2 Genetic Crosses Predicting Results of Monohybrid Crosses, continued • Incomplete dominance two or more alleles influence the phenotype and results in a phenotype are intermediates between the dominant trait and the recessive trait (so there is a blending of alleles). 1. Red snapdragon is crossed with pink snapdragon, what are the possible genotypes and phenotypes? 2. Pink snapdragon is crossed with white snapdragon, what are the possible genotypes and phenotypes? Chapter 9 Section 2 Genetic Crosses Predicting Results of Monohybrid Crosses, continued • Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring. COWS: BB = Black BW = Black and White WW = White Cross a black male with a black and white female, determine the possible genotype and phenotypes for the offspring? • II. Solving Genetic Problems A. Probability and Genetics: already covered B. Incomplete Dominance C. Codominance D. Multiple Alleles 1. more than just two alleles 2. Examples: Coat Color in Chinchillas Cross a Light Gray Chinchilla (c genotypes and phenotypes? ch h h h c ) with a Himalayan (c c ) Chinchilla, what are the possible Chapter 9 Section 2 Genetic Crosses Predicting Results of Dihybrid Crosses • Dihybrid cross two traits are tracked at the same time. Round (R) is dominant to wrinkled (r) Green (G) is dominant to yellow (g) Homozygous round yellow pea plant is crossed with wrinkled homozygous green pea plant, what are the possible genotypes and phenotypes of the offspring. Parents ______________ x __________________ Possible Gametes Genotype: Phenotype: Round (R) is dominant to wrinkled (r) Green (G) is dominant to yellow (g) Heterozygous round heterozygous green pea plant is crossed with Heterozygous round heterozygous green pea plant , what are the possible genotypes and phenotypes of the offspring. Parents ____________________ x _______________________ Possible Gametes Genotype: Phenotype: Heterozygous round heterozygous green pea plant is crossed with Heterozygous round heterozygous green pea plant , what are the possible genotypes and phenotypes of the offspring. Parents ____________________ x __________________________ Chapter 9 Dihybrid Crosses Section 2 Genetic Crosses Chapter 9 Section 2 Genetic Crosses Objectives • Differentiate between the genotype and the phenotype of an organism. • Explain how probability is used to predict the results of genetic crosses. • Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses. • Explain how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait. • Differentiate a monohybrid cross from a dihybrid cross. I. Principles of Genetics A. HEREDITY B. Origin of Genetic C. Mendel’s Experiment D. Mendel’s Results E. Mendel’s Hypothesis F. Terminology G. Simple Monohybrid Crosses 1. Complete Dominance 2. Incomplete Dominance 3. Codominance H. Dihybrid Cross : Principle of Independent Assortment