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Activity 6-1 Expression: Dominant and Recessive

PLAN

Summary Students learn how gene expression for a particular trait is influenced by dominant and recessive alleles. They use red and white beans to represent two alleles for bean color. The red is the dominant allele (R), while the white is the recessive allele (r). Through 15 random selections of beans (alleles), from parents who are both heterozygous for the trait, students record the genotype and the resulting phenotype of the offspring. They recognize that there is a random assortment of allele combinations each time an offspring is created. They analyze the pattern of inheritance of this trait in offspring from heterozygous parents, and then compare it to the pattern of inheritance of this trait in offspring from one parent who is homozygous for the trait, while the other is heterozygous.

Objectives

Students:

\checkmark record the results of 15 random draws from the two gene pools.

\checkmark explain that for each offspring produced, there is a random selection of the allele contributed by each parent.

\checkmark predict which variation will be expressed in each offspring based on the genotypes drawn.

\checkmark calculate the percent of each genotype and each phenotype in the 15 offspring.

\checkmark explain the inheritance pattern of the recessive allele.

Student Materials

  • Activity Report
  • 20 white beans
  • 20 red beans
  • 2 jars or cups
  • Paper and pen/pencil

Teacher Materials

Activity 6-1: Expression: Dominant and Recessive

  • Activity Report Answer Key

Advance Preparation

  1. Obtain red and white beans and place 10 of each color in a separate cup.
  2. Gather one set of student materials for each group of students.
  3. Have extra red and white beans available.
  4. Coordinate this interdisciplinary activity with the math teacher.

Estimated Time One class period

Interdisciplinary Connection

Math Complete activities relating to probability, calculating percentages, and fractions in math class.

Prerequisites and Background Information

Students should know how to calculate percentages or have some skills working with fractions. Students should know how to use a table.

IMPLEMENT

Step 1 Instruct students to put the beans back in the jars after they have made each selection as all 20 beans need to be in each jar at the time of each draw.

Consider the case where one parent is homozygous with the dominant allele. Ask students to answer this question without performing the experiment, writing their responses on the Student Report or discussing the consequences in class.

Steps 2-5 Continue to emphasize that each draw represents a chance (random) event.

Steps 6-9 Make sure students are recording their choices and completing the Activity Report.

Extend Activity 6-1 by having students build an imaginary animal. They decide on 4 traits and determine what the dominant and recessive alleles are for those traits. Then they assign the dominant allele to the red bean and the recessive to the white bean for each trait. They continue as before but now every 4 draws represents the expression of the four traits of the imaginary animal. The following is an example:

Helpful Hints

  • Guide students in using their tables for recording data.
  • The beans can be replaced with small balls of crumpled paper of two colors.
ANIMAL: Snuggleuptous
TRAIT DOMINANT RECESSIVE
hair curly (C) straight (c)
tail long (L) short (I)
color black (B) white (b)
height tall (T) short (t)

ASSESS

Use the completion of the activity, the analysis of the data tables, and the answers on the Activity Report to assess if students can

\checkmark accurately record data on the 15 offspring produced for the two different cases presented.

\checkmark explain that for each offspring produced, there is a random selection of the allele contributed by each parent.

\checkmark predict which variation of the trait will be expressed in each offspring based on its genotype.

\checkmark calculate the percent of each genotype and each phenotype in the 15 offspring for the two different cases presented.

\checkmark explain the inheritance pattern of the recessive allele.

Activity 6-1 Expression: Dominant and Recessive Activity Report Answer Key

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. Record your observations in the table below.
  2. Color of 1st bean Color of 2nd bean Gene pattern (genotype) Color pattern (phenotype)
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
  3. Record your observations in the table below
  4. Color of 1st bean Color of 2nd bean Gene pattern (genotype) Color pattern (phenotype)
    1
    2
    3
    4
    5
    6
    7
    8
    9
    10
    11
    12
    13
    14
    15
  5. What do the jars containing the 20 beans represent?
  6. Why was only one bean at a time taken out of each jar?
  7. What does the pair of genes represent?
  8. Refer to Table 1. List all possible phenotypes and genotypes.
  9. Refer to Table 1. Calculate the percent for each phenotype and for each genotype by using the formula: number observed divided by the total number times 100. List the percentages of each phenotype and genotype below:
  10. After completing the 15 crosses between the jar with 20 white beans and the one with 10 red and ten white (Step 8), look at the data in Table 2 and explain why so many more pairs of white were drawn, considering white represents the recessive allele for the trait.

What Do You Think?

The phrase “Every human gene must have an ancestor” is found in the book Language of Genes. What does the phrase mean to you? Write a story or poem about real or imagined ancestors who might have had one or more variations you carry in your DNA today. Be creative. Have fun imagining who these people might have been and what they might have been like.

A suggested response will be provided upon request. Please send an email to teachers-requests@ck12.org.

Sometimes a baby with blue eyes is born to two parents with brown eyes. Grandparents smile and say “blue eyes skip a generation.” Is this myth correct? Can you explain how two brown-eyed parents could have a blue-eyed child?

Using Punnett squares, show the results of crossing a homozygous tall (TT) and a homozygous short (tt) pea plant. Then show the results of back crossing the \mathrm{F}_1 pea plants to each parental type.

&\text{Parents} && \text{Tall pea plant = IT}\\&&& \text{Short pea plant = tt}\\&\text{Gametes} && \text{Tt}

Use the Punnett square technique to show the results of crossing a tall pea plant with two tall alleles (TT) that has two alleles for wrinkled seeds (rr) with a short pea plant (tt) that has two alleles for round seeds (RR).

&\text{Parents} && \text{TTrr} \times \text{ttRR}\\&\text{Gametes} && \text{Tr} \qquad \ \text{tR}

What do you think is the importance of genetic maps?

Review Questions/Answers

  • Sample answers to these questions will be provided upon request. Please send an email to teachers-requests@ck12.org to request sample answers.
  1. What are alleles? Why are they important?
  2. What is the difference between dominant and recessive alleles?
  3. Although Gregor Mendel didn't know about meiosis or mitosis, his discoveries provided the foundation for modern genetics. What did he find?

Activity 6-1 Report Expression: Dominant and Recessive (Student Reproducible)

1. Record your observations in the table below.

Color of 1st bean Color of 2nd bean Gene pattern (genotype) Color pattern (phenotype)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

2. Record your observations in the table below.

Color of 1st bean Color of 2nd bean Gene pattern (genotype) Color pattern (phenotype)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

3. What do the jars and the beans represent?

4. Why was only one bean at a time taken out of each jar?

5. What does the pair of genes represent?

6. Refer to Table 1. List all possible phenotypes and genotypes.

7. Refer to Table 1. Calculate the percent for each phenotype and for each genotype by using the formula: number observed divided by the total number times 100. List the percentages of each phenotype and genotype below:

8. After completing the 15 crosses between the jar with 20 white beans and the one with 10 red and 10 white (Step 8), look at the data in Table 2 and explain why so many more pairs of white were drawn, considering white represents the recessive allele for the trait.

Image Attributions

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Authors:

Grades:

6 , 7 , 8

Date Created:

Feb 23, 2012

Last Modified:

Apr 29, 2014
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