Section 1 Mendel’s Legacy Chapter 9 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.

Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel The study of how characteristics are transmitted from parents to offspring is called genetics. Mendel is considered to be the “father” of genetics because of all of his work with heredity Heredity is the passing of traits from parents to their offspring

Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued Mendel’s Garden Peas –Mendel observed characteristics of pea plants. –Traits are genetically determined variants of a characteristic. –Each characteristic occurred in two contrasting traits.

Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued Mendel’s Methods –Self-pollination occurs when pollen is transferred from the anthers (male) of a plant to the stigma (female) of the same plant –Cross-pollination occurs when pollen is transferred between flowers of two different plants Mendel controlled his experiments by manually pollinating the other plants through cross-pollination, he removed anthers from the plants he was working with

Section 1 Mendel’s Legacy Chapter 9 Mendel’s Experiments Mendel bred plants for several generations that were true-breeding (self-pollinating) for specific traits and called these the P generation. –True breeding pea plants always produce offspring each of which can have only one form of a trait –Ex. True-breed pea plants with yellow pods will self- pollinate and produce offspring with yellow pods Offspring of the P generation were called the F 1 generation. Offspring of the F 1 generation were called the F 2 generation.

Chapter 9 Three Steps of Mendel’s Experiments Section 1 Mendel’s Legacy Pg 175 Figure 9-3

Chapter 9 Click below to watch the Visual Concept. Visual Concept Mendel’s Experiments Section 1 Mendel’s Legacy

Chapter 9 Mendel’s Results and Conclusions Recessive and Dominant Traits –Mendel concluded that inherited characteristics are controlled by factors that occur in pairs. –In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.

Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued The Law of Segregation –The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes. Law of segregation is used to describe how traits can disappear and reappear in a certain pattern from generation to generation

Section 1 Mendel’s Legacy Chapter 9 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 separate chromosomes or are far apart on the same chromosome.

Section 1 Mendel’s Legacy Chapter 9 Support for Mendel’s Conclusions We now know that the factors that Mendel studied are alleles, or alternative forms of a gene. One allele for each trait is passed from each parent to the offspring. –We can see this by looking at ourselves in comparison to our parents, we may have some of both our mother and father –We will study this further with Punnett Squares in 9-2

Chapter 9 Click below to watch the Visual Concept. Visual Concept Mendel’s Conclusions Section 1 Mendel’s Legacy

SECTION 9.1 REVIEW PG 178 #1-8 Homework

Section 2 Genetic Crosses Chapter 9 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.

Section 2 Genetic Crosses Chapter 9 Genotype and Phenotype The genotype is the genetic makeup of an organism. The phenotype is the appearance of an organism. Homozygous – when both alleles of a pair are alike Heterozygous – when two alleles in a pair are different

Section 2 Genetic Crosses Chapter 9 Probability Probability is the likelihood that a specific event will occur. –Probability equation page 181 A probability may be expressed as a decimal, a percentage, or a fraction.

Chapter 9 Click below to watch the Visual Concept. Visual Concept Calculating Probability Section 2 Genetic Crosses

Chapter 9 Predicting Results of Monohybrid Crosses 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. –Figures 9-7 and 9-8 pg 182 Genotypic ratio is the ratio of genotypes that appear in offspring Phenotypic ratio is the ratio of offspring’s phenotypes

Chapter 9 Click below to watch the Visual Concept. Visual Concept Punnett Square with Heterozygous Cross Section 2 Genetic Crosses

Chapter 9 Monohybrid Cross of Heterozygous Plants Section 2 Genetic Crosses

Chapter 9 Section 2 Genetic Crosses Y = Yellow y = Green (non-yellow) What is the genotypic ratio for this monohybrid cross? What is the phenotypic ratio for this monohybrid cross?

Chapter 9 Section 2 Genetic Crosses Y = Yellow y = Green (non-yellow) What is the genotypic ratio for this monohybrid cross? 1:2:1 What is the phenotypic ratio for this monohybrid cross? 3 yellow : 1 green 3:1

Section 2 Genetic Crosses Chapter 9 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 Click below to watch the Visual Concept. Visual Concept Testcross Section 2 Genetic Crosses

Chapter 9 Predicting Results of Monohybrid Crosses, continued Complete dominance occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype. Ex. Both pea plants PP and Pp for flower color have purple flowers

Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Incomplete dominance occurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait. In four o’clock flowers, red flowers (R) self-pollinate and only produce red offspring, while white flowers (R’) self- pollinate and only produce white offspring IF, red (R) and white (R’) are crossed they will produce 100% pink (RR’) offspring

Section 2 Genetic Crosses Chapter 9 Predicting Results of Monohybrid Crosses, continued Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring. Four human ABO blood types, A, B, and AB and O, are determined by three alleles. The letters A and B refer to two molecules on the surface of the red blood cell. The genotype of a person with blood type AB is I A I B, and neither allele is dominant over the other type. Type AB blood cells carry both A- and B-types of molecules on their surface.

Section 2 Genetic Crosses Chapter 9 Predicting Results of Dihybrid Crosses A cross in which two characteristics are tracked is a dihybrid cross. –To create this type of cross we will use the FOIL method to be used in a 4x4 Punnett Square

Chapter 9 Dihybrid Crosses Section 2 Genetic Crosses

SECTION 9.2 REVIEW PG 186 #1-7 Homework