Unit 2 Lesson 4 Heredity Copyright © Houghton Mifflin Harcourt Publishing Company *

Give Peas a Chance What is heredity? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

How are traits inherited? 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 * *

What are the exceptions to complete dominance? 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 * *

What are the exceptions to complete dominance? 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 * *