Chapter 4 Objectives Content Explain the relationship between traits and heredity. Explain the difference between dominant and recessive traits. Language Describe the experiments of Gregor Mendel. Section 1 Mendel and His Peas

Chapter 4 What is Heredity? Who discovered it?

Chapter 4 Who Was Gregor Mendel? Gregor Mendel was born in 1822 in Heinzendorf, Austria. At age 21, Mendel entered a monastery. He performed many scientific experiments in the monastery garden. Mendel discovered the principles of heredity, the passing of traits from parents to offspring. Section 1 Mendel and His Peas

Chapter 4 Unraveling the Mystery Mendel used garden pea plants for his experiments. Self-Pollinating Peas have both male and female reproductive structures. So, pollen from one flower can fertilize the ovule of the same flower. When a true-breeding plant self pollinates, all of the offspring will have the same trait as the parent. Section 1 Mendel and His Peas

Chapter 4 Pea plants can also cross-pollinate. Pollen from one plant fertilizes the ovule of a flower on a different plant. The image below shows cross- pollination and self-pollination. Section 1 Mendel and His Peas

Chapter 4 Characteristics Mendel studied only one pea characteristic at a time. A characteristic is a feature that has different forms in a population. Different forms of a characteristic are called traits. Section 1 Mendel and His Peas

Chapter 4 Mix and Match Mendel was careful to use plants that were true breeding for each of the traits he was studying. By doing so, he would know what to expect if his plants were to self-pollinate. Section 1 Mendel and His Peas

Chapter 4 Mendel’s First Experiments Mendel crossed pea plants to study seven different characteristics. Mendel got similar results for each cross. One trait was always present in the first generation, and the other trait seemed to disappear. Mendel called the trait that appeared the dominant trait. The trait that seemed to fade into the background was called the recessive trait. Section 1 Mendel and His Peas

Chapter 4 Mendel’s First Experiments Mendel crossed pea plants to study seven different characteristics. Mendel got similar results for each cross. One trait was always present in the first generation, and the other trait seemed to disappear. Mendel called the trait that appeared the dominant trait. The trait that seemed to fade into the background was called the recessive trait. Section 1 Mendel and His Peas

Chapter 4 Mendel’s Second Experiments To find out more about recessive traits, Mendel allowed the first-generation plants to self-pollinate. In each case some of the second- generation plants had the recessive trait. Section 1 Mendel and His Peas

Chapter 4 Ratios in Mendel’s Experiments The recessive trait did not show up as often as the dominant trait. Mendel decided to figure out the ratio of dominant traits to recessive traits. Section 1 Mendel and His Peas

Chapter 4 In all cases the ratio was about ____:____ dominant : recessive.

Chapter 4 Mendel’s Second Experiments Gregor Mendel – Gone But Not Forgotten Mendel realized that his results could be explained only if each plant had two sets of instructions for each characteristic. Mendel’s work opened the door to modern genetics. Section 1 Mendel and His Peas

Chapter 4 Bellringer If you flip a coin, what are the chances that it will land on heads? tails? Suppose that you flipped the coin and got heads. What are the chances that you will get heads again? Record your answers in your science journal. Section 2 Traits and Inheritance

Chapter 4 Objectives Explain how genes and alleles are related to genotype and phenotype. Use the information in a Punnett square. Explain how probability can be used to predict possible genotypes in offspring. Describe three exceptions to Mendel’s observations. Section 2 Traits and Inheritance

Chapter 4 Genes are found on the chromosomes(DNA) of an individual. Genes are the instructions for an inherited trait. The different forms (often dominant or recessive) of a gene are alleles. Pea plants have a gene for flower color, the alleles are either purple(Dominant) or white(recessive) Section 2 Traits and Inheritance

Chapter 4 Genotype The combination of inherited alleles together form an organism’s genotype. We use letters to represent the Alleles of a genotype The letter is chosen based on the name of the dominant trait Capitol letter for a dominant allele Lowercase letter for a recessive allele Ex: Purple flowers is a dominant trait in pea plants so we use a capitol P for Dominant and a lower case p for Recessive Chromosomes work in pairs so you have two copies of each allele resulting in three possible genotypes Section 2 Traits and Inheritance

Chapter 4 Possible Genotypes Ex : Flower color in peas Homozygous Dominant (PP) Both alleles are dominant Homozygous Recessive (pp) Both alleles are recessive Heterozygous (Pp) One dominant and one recessive allele

Chapter 4 Phenotype is an organism appearance due to its genotype Different Genotypes result in different Phenotypes Homozygous Dominant will show the Dominant Phenotype Homozygous Recessive will show the Recessive Phenotype Heterozygous will show the Dominant Phenotype PP = pp = Pp=

Chapter 4 Punnett Squares are used to organize all the possible genotype combinations of offspring from particular parents.

Chapter 4 Section 2 Traits and Inheritance

Chapter 4 What Are the Chances? Probability is the mathematical chance that something will happen. Probability is most often written as a fraction of percentage. Section 2 Traits and Inheritance

Chapter 4 Calculating Probability Section 2 Traits and Inheritance

Chapter 4 More About Traits Incomplete Dominance Researchers have found that sometimes one trait is not completely dominant over another. One Gene, Many Traits Sometimes one gene influences more than one trait. Many Genes, One Trait Some traits, such as the color of your skin, hair, and eyes, are the result of several genes acting together. Section 2 Traits and Inheritance

Chapter 4 More About Traits, continued The Importance of Environment Genes aren’t the only influences on traits. A combination of things determine an individual’s characteristics. Your environment also influences how you grow. Lifestyle choices can also affect a person’s traits. Section 2 Traits and Inheritance