Chapter 5 Heredity Table of Contents Section 1 Mendel and His Peas Section 2 Traits and Inheritance Section 3 Meiosis Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Objectives • Explain the relationship between traits and heredity. • Describe the experiments of Gregor Mendel. • Explain the difference between dominant and recessive traits. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Unraveling the Mystery, continued • 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 selfpollination. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Unraveling the Mystery, continued • 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Unraveling the Mystery, continued • 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Mendel’s Second Experiments, continued • 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Mendel’s Second Experiments, continued In all cases the ratio was about 3:1 dominant : recessive. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved. Chapter 5 Section 1 Mendel and His Peas Mendel’s Second Experiments, continued • 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. Chapter menu Resources Copyright © by Holt, Rinehart and Winston. All rights reserved.
