Materials

  • CCB Science pages 184 - 193

Standards

Objectives

  • Use a Punnet Square to determine an organism’s genotype and phenotype

  • Explain the relationship between genotype and phenotype

  • Describe the role of alleles

Key Concept

  • Traits, or characteristics, are transmitted from one generation to the next. This transmission is called heredity. The young, also called offspring, resemble their parents. However, there are also differences, or variations, between them. The traits we observe in an organism represent its phenotype. The genetic information underlying the phenotype is called the genotype.

Vocabulary

Tier 2 heredity
offspring
Tier 3 allele
genotype
phenotype
Punnet square
Test Words distinguish

Evidence-Based Reading

  • Base Words: Emphasize how understanding the meaning of word parts can help them determine the meaning of complex words, especially science words. Write the Latin word dominant on the board, and explain that it means ruling, or governing. Write the Latin word ‘recedere’ on the board, and explain that it means to go back, or withdraw. Write the words dominant and recessive on the board. Tell students that you want them to underline or highlight these words the first time they appear on the page.

21st Century Skill

  • Leadership and Responsibility: Invite volunteers to read paragraphs of the text aloud. Ask students what hobbies or pursuits they participate in that require special safety equipment.

Writing Practice

  • Before students write, encourage them to review the lesson to locate important details that will help them define genotypes and phenotypes. Also have them search for specific examples they can use to support their definitions.

Before Lesson

Determine students’ readiness by engaging them in a discussion of an organism’s DNA, or deoxyribonucleic acid. Students should know that instructions for determining an organism’s traits, or characteristics, are found in its DNA, and that they inherit their DNA from their parents. Encourage students to discuss traits they share vii.th family members, or traits that their pets share with their offspring.

Background

An organism’s traits, or characteristics, are passed from parents to their offspring on chromosomes. Chromosomes are threads of proteins and a substance called DNA that contains small sections called genes. Each gene lives in a specific spot, or locus, on a chromosome. Help students recall their discussion of genes. Ask them to explain why some people refer to genes as instruction manuals for life.

Guided Practice

  • The Science of Heredity
    • Heredity and the Allele
    • The Punnet Square
    • X-Linked Inheritance
    • Exceptions to Dominance

Core Skill

Distinguish Among Reasoned Judgments: Remind students that a scientific conclusion is based on evidence, and when that evidence varies, so do conclusions. Help students to see that as scientists continue investigating, and as new technologies assist them in their work, more evidence becomes available. That evidence may help explain varying conclusions, or help scientists reconcile different conclusions to form a new conclusion.

Express Scientific Information: Observe students as they work, intervening if necessary to guide their understanding.

Extension

Review a Procedure: Ask students to turn to page 191, the procedure for extracting strawberry DNA. Ask students to summarize the steps in the investigation in the order they occurred. Have them describe the safety precautions they took while conducting the task. Invite students to discuss the results and any observations they made that they found particularly interesting.

Compare Data: Have students locate a print or online investigation that explains how to extract DNA from a fruit other than strawberries. Have students compare the procedures before they conduct the investigation they find. Ask students to summarize the similarities and differences between the two investigations and the results.

Lesson Review