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Transcript
Unit 2 Lesson 4 Heredity Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity Give Peas a Chance What is heredity? • Traits, such as hair color, result from the information stored in genetic material. • Heredity is the passing of genetic material from parents to offspring. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity How are traits inherited? • Genes are segments of DNA. They give instructions for producing a certain characteristic. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity How are traits inherited? • 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. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity How are traits inherited? • 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. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity How are traits inherited? • The combination of alleles that you inherited from your parents is your genotype. • Your observable traits make up your phenotype. • The phenotypes of some traits follow patterns similar to the ones Mendel discovered. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity 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. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity 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. • This is called complete dominance. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity How are traits inherited? • Some characteristics are a result of several genes acting together. • Sometimes, one gene influences more than one trait. • For example, many genetic disorders, such as sickle cell anemia, are linked to a single gene but affect many traits. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity How are traits inherited? • Sometimes, the environment can influence an organism’s phenotype. • Some traits are acquired only from one’s environment and are not inherited. • For example, your ability to read and write is an acquired trait. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity 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. Copyright © Houghton Mifflin Harcourt Publishing Company Unit 2 Lesson 4 Heredity 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. Copyright © Houghton Mifflin Harcourt Publishing Company