Activity 4 Breeding Corn

BELL RINGER If a green pea pod plant is crossed with a yellow pea pod plant, what will the offspring look like? X ALL the offspring will be green!

Is it possible for a man & woman (each with dark hair) to have a child with blond hair?

Read the Introduction…Pg. 282 What is SELECTIVE BREEDING? What is SEXUAL REPRODUCTION? the process by which organisms with desirable traits are mated with the goal of producing even more desirable offspring. reproduction in which two parents contribute genetic material to the offspring.

Corn Reproductive Structures Explain how sexual reproduction in corn happens. For more information see your Teacher’s Edition for this activity. This image can be found on Transparency 4.3, “Corn Reproductive Structures.” Note: It is a common misconception that corn kernels are gametes. Make sure your students understand that each kernel is a fertilized offspring, or embryo.

How do traits get passed from parent to offspring? Through GAMETES: sex cells Male gamete is the SPERM Female gamete is the EGG FERTILIZATION: union of egg & sperm ZYGOTE: fertilized egg

Challenge How can information about the genetic makeup of plants help farmers breed plants for desirable traits?

Answer the 3 questions on the “Traits & Heredity” sheet under “I think…”

Breeding Corn: First Generation Procedure Steps 1-14 are an opportunity for you to use the Group Interaction (GI) Scoring Guide to assess students’ group interaction skills. For more information see the Teacher’s Edition for this activity and Teacher Resources IV: Assessment. Pedigrees are introduced formally in Activity 8, “Interpreting Pedigrees.” Refer to the slide to clarify students’ questions before they begin work in Procedure Step 2. For more information see your Teacher’s Edition for this activity. Be sure students have completed Procedure Step 2 before continuing to the next slide. This image can be found in Transparency 4.1, “Breeding Corn: First Generation.”

Read “Basic Genetics” on p. 286 What are alleles? Distinguish between dominant and recessive traits. A form of a gene…An organism has two copies of the gene for each of its traits. Be sure students understand clearly the terms allele, dominant and recessive and how to depict genes with letters before they move on to Punnett squares. For more information see your Teacher’s Edition for this activity. Dominant traits will mask another version of a trait; only one dominant allele needed to be expressed… A recessive trait will be hidden by a dominant trait.

GENES VS. ALLELES Segment of DNA that codes for one protein/trait Most traits are determined by TWO genes. Remember chromosomes have a homologous match…two chromosomes with similar genetic information EXAMPLE: hair color eye color height in pea plants Each form of a gene is called an ALLELE EXAMPLE: brown or blond blue, hazel, brown tall, short

Always expressed if present RECESSIVE (allele) May be present but will not be expressed if paired w/ dominant allele Requires TWO recessive alleles for recessive trait to be expressed EXAMPLES: light hair, blue eyes, short peas DOMINANT (allele) Always expressed if present Only need ONE dominant allele to be expressed EXAMPLES: dark hair, brown eyes, tall peas

As a group… Use the “P” allele cards to demonstrate what happened to make all corn kernel babies purple Discuss the 3 questions as a group and fill in under “My group thinks…”

Creating a Punnett Square Use as necessary to review how to show the results of a cross. See your Teacher’s Edition for this activity for more information. This image can be found on Transparency 4.4, “Creating a Punnett Square.” See your Teacher’s Edition for this activity for information on reviewing the ratios in Steps 7, 10 and 11.

All possible combinations using P, p: PP, pp, Pp, pP Genotype vs. Phenotype All possible combinations using P, p: PP, pp, Pp, pP GENOTYPE: actual genes in the pair; can’t see…they’re on chromosomes…but they determine the individual’s traits PHENOTYPE: the trait that is expressed; the ‘physical’ appearance

Describing GENOTYPE… Use terms: homozygous: both genes the same (PP, pp) *follow with ‘dominant’ or ‘recessive’ to distinguish upper case or lower case heterozygous: genes different; 1 dominant, 1 recessive (Pp, pP)

Read the scenario (step 8 on p.286) Count the number of purple kernels and the number of yellow kernels on corn ear A Record your data Count the number of purple kernels and the number of yellow kernels on corn ear B

Which describes the cross that produced ear A? Ear B? Students’ responses to Procedure Steps 16 and 17 may be scored with the Analyzing Data (AD) Scoring Guide. For more information see your Teacher’s Edition for this activity and Teacher Resources IV: Assessment. Students should conclude that the cross shown in Punnett Square Z produced the kernels on ear A and the cross shown in Punnett Square Y produced the kernels on ear B. Have the class conduct an Informal Meeting of the Minds to compare their results and conclusions. For more information on how to do this see your Teacher’s Edition for this activity. Punnett Square X Punnett Square Y Punnett Square Z

Breeding Corn: Second Generation You may wish to review what students know about each cross, including the allele combinations of the parents and offspring, if they do not come to an agreement. This image can be found on Transparency 4.2, “Breeding Corn: Second Generation.”

Complete the “now we know” column of the “traits & Heredity” page Answer the ANALYSIS questions p.289

Analysis 1 How does a Punnett square show the possible results of a cross between two individuals? Analysis Question 1 will help you gauge students understanding of heredity and the use of Punnett squares. A sample student response can be found in the Teacher’s Edition for this activity.

Analysis 2 Describe how your observations of offspring (corn kernels) allowed you to determine the genetic makeup of the two parents. Discuss how you used ratios in this process

Analysis 3 What do you predict will happen if a purple corn plant with the genes Pp is bred with a corn plant with purple kernels and the genes PP? Explain your answer, and include a matching Punnett Square. Analysis Question 3 will help you gauge students understanding of heredity and the use of Punnett squares. A sample student response can be found in the Teacher’s Edition for this activity.

Analysis 4 How could scientists use selective breeding to help solve a sustainability challenge such as breeding a crop that can survive drought? Analysis Question 4 may be scored using the Understanding Concepts (UC) Scoring Guide. A sample student response and more information can be found in the Teacher’s Edition for this activity and in Teacher Resources IV: Assessment.

Revisit the Challenge How can information about the genetic makeup of plants help farmers breed plants for desirable traits? Return students to Student Sheet 4.1, “Traits and Heredity,” and ask them to complete the “Now we know…” column. More information and a sample student response may be found in the Teacher’s Edition to this activity.

allele dominant Punnett square recessive selective breeding Key Vocabulary allele dominant Punnett square recessive selective breeding sexual reproduction trait See Teacher Resources III: Literacy for more information on key vocabulary and the most effective strategies to enhance student vocabulary learning. Note that bold words are formally defined in this activity. Words in regular font are used in the activity, but not formally defined. The definition of a key vocabulary word should not be discussed as a class prior to the formal definition being introduced.