Unit 2 Lesson 4 Heredity Essential Question: How are traits inherited?

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1 Big Idea: Characteristics from parents are passed to offspring in predictable ways Unit 2 Lesson 4 Heredity Essential Question: How are traits inherited? Copyright Houghton Mifflin Harcourt Publishing Company

2 Give Peas a Chance What is heredity? P124 Traits, such as hair color, result from the information stored in genetic material. Heredity is the passing of genetic material from parents to offspring. What did Gregor Mendel discover about heredity? Gregor Mendel was an Austrian monk. In the 1800s, Mendel performed the first major experiments in heredity.

3 P124 What did Gregor Mendel discover about heredity? Mendel studied seven characteristics of pea plants. plant height, flower and pod position, seed shape, seed color, pod shape, pod color, and flower color. A characteristic is a feature that has different forms in a population. Each characteristic had two different forms. These different forms are called traits. Is flower color a characteristic or a trait? Characteristic

4 P125 What did Gregor Mendel discover about heredity? Mendel studied each characteristic separately, always starting with plants that were true-breeding. True-breeding plants always produce offspring with the same trait if allowed to self-pollinate naturally.

5 P124 What did Gregor Mendel discover about heredity? Mendel crossed plants that were true-breeding for producing yellow seed pods with plants that were truebreeding for green seed pods. All of the plants from the first generation produced green seed pods. Mendel called the green seed pod the dominant trait, and the yellow seed pod the recessive trait.

6 P125 What did Gregor Mendel discover about heredity? Next, Mendel let the first generation plants self-pollinate. Out of the generation that resulted, called the second generation, about three-fourths had green seed pods and one-fourth had yellow pods. The recessive trait had seemed to disappear in the first generation, but it reappeared in the second generation.

7 P125 What did Gregor Mendel discover about heredity? Mendel hypothesized that each plant must have two heritable factors for each trait, one from each parent. Some traits, such as yellow color (Recessive), could only be observed if a plant had two of the same factors. A plant with two different factors would show the dominant factor but be able to pass on both factors to its offspring.

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9 It s in Your Genes! How are traits inherited? P126 1) Genes are passed from parent to offspring 2) Genes Influence Traits 3) Many Genes can influence a single trait 4) Single gene can influence many traits 5) Environment can Influence Traits

10 P126 1) Genes are passed from parent to offspring It s in Your Genes! How are traits inherited? Mendel s ideas can be further explained by our modern understanding of DNA. What Mendel called factors are actually segments of DNA known as genes. Genes are segments of DNA. They give instructions for producing a certain characteristic

11 P126 How are traits inherited? 1) Genes are passed from parent to offspring The offspring has two versions of the same gene for every characteristic one from each parent. Different versions of a gene are known as alleles. Dominant alleles are shown with a capital letter, and recessive alleles are shown with a lowercase version of the same letter. An organism with one dominant and one recessive allele for a gene is heterozygous for that gene. An organism with two of the same alleles for a gene is homozygous for that gene.

12 P127 2) Genes Influence Traits How are traits inherited? The combination of alleles that you inherited from your parents is your genotype. Your observable traits make up your phenotype.

13 P127 2) Genes Influence Traits How are traits inherited? The dominant allele contributes to the phenotype if one or two copies are present in the genotype. The recessive allele contributes to the phenotype only when two copies of it are present.

14 P127 2) Genes Influence Traits How are traits inherited?

15 P127 2) Genes Influence Traits How are traits inherited? If one chromosome in the pair contains a dominant allele and the other contains a recessive allele, the dominant allele determines the phenotype. complete dominance.

16 P128 3) Many Genes can influence a single How are traits inherited? trait Some characteristics are a result of several genes acting together. Different combinations of alleles can result in different shades of eye color or even skin color.

17 P128 How are traits inherited? 4) Single gene can influence many traits Sometimes, one gene influences more than one trait. Vision and Skin problems many genetic disorders, such as sickle cell anemia, are linked to a single gene but affect many traits. Protein in RBC Damage spleen Not able to deliver oxygen to organs

18 P129 5) Environment can Influence How are traits inherited? Traits Sometimes, the environment can influence an organism s phenotype. Arctic fox gene (protein) reacts to amount of sunlight. Traits that are learned in one s environment are not inherited. Learn how to read, write, play basketball

19 Bending the Rules P130 What are the exceptions to complete dominance? Some traits do not follow the pattern of complete dominance. For traits that show incomplete dominance and codominance, one trait is not completely dominant over another.

20 P130 What are the exceptions to complete dominance? In incomplete dominance, each allele in a heterozygous individual influences the phenotype. The result of incomplete dominance is a phenotype that is a blend of the phenotypes of the parents.

21 P131 What are the exceptions to complete dominance? For a trait that shows codominance, both of the alleles in a heterozygous individual contribute to the phenotype. Heterozygous individuals have both of the traits associated with their two alleles.

22 P131 What are the exceptions to complete dominance? Human blood type is an example of codominance. Three alleles, called A, B, and O, play a role in determining blood type. A person with an A allele and a B allele has type AB blood.