Lesson 2 | Understanding Inheritance

Genetics 25

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Student Labs and Activities Page

Launch Lab 26

Content Vocabulary 27

Lesson Outline 28

MiniLab 30

Content Practice A 31

Content Practice B 32

Language Arts Support 33

School to Home 35

Key Concept Builders 36

Enrichment 40

Challenge 41

Skill Practice 42

Lesson 2 | Understanding Inheritance

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What is the span of your hand?Mendel discovered that some traits have a simple pattern of inheritance—dominant or recessive. However, some traits, such as eye color, have more variation. Is human hand span a Mendelian trait?

Procedure

Launch Lab LESSON 2: 15 minutes

Data and Observations

Think About This 1. What range of hand span measurements did you observe?

2. Key Concept Do you think hand span is a simple Mendelian trait like pea plant flower color?

1. Read and complete a lab safety form.

2. Use a metric ruler to measure the distance (in cm) between the tips of your thumb and little finger with your

hand stretched out. Record your measurement below.

3. As a class, record everyone’s name and hand span in a data table.

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Understanding Inheritance Directions: Answer each question or respond to each statement on the lines provided. Use complete sentences.

1. What is the difference between a phenotype and a genotype?

2. What does the term conclude mean?

3. Describe the difference between a homozygous genotype and a heterozygous genotype.

4. How does incomplete dominance differ from codominance?

5. What is the relationship between an allele and a gene?

6. What is the purpose of a Punnett square?

7. Give an example of a trait that is passed through polygenic inheritance.

Content Vocabulary LESSON 2


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Understanding InheritanceA. What controls traits?

1. Inside each cell is a nucleus that contains threadlike structures

called .

2. Mendel’s factors are parts of chromosomes, and each cell in the offspring contains

chromosomes from both .

3. A(n) is a section on a chromosome that has genetic information for one trait.

4. The different forms of a gene are called .

5. Geneticists refer to how a trait appears, or is expressed, as the

trait’s .

6. The two alleles that control the phenotype of a trait are called the

trait’s .

a. In genetics, letters represent dominant alleles, and

letters represent recessive alleles.

b. When two alleles of a gene are the same, its genotype is .

c. If two alleles of a gene are different, its genotype is .

B. Modeling Inheritance

1. In a situation based on chance, such as flipping a coin, the chance of getting

a certain outcome can be represented by a(n) such as 50:50, or 1:1.

2. A(n) is a model that is used to predict possible genotypes and phenotypes of offspring.

a. To create a Punnett square, you need to know the of both parents.

b. If you count large numbers of from a particular cross, the overall ratio will be close to the ratio predicted by a Punnett square.

3. A(n) is a diagram that shows phenotypes of genetically

related family members. It also gives clues about their .

Lesson Outline LESSON 2


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Lesson Outline continued

C. Complex Patterns of Inheritance

1. Alleles show when the offspring’s phenotype is a blend of the parents’ phenotypes.

2. Alleles show when both alleles can be observed in a phenotype.

3. Unlike the genes in Mendel’s pea plants, some genes have alleles.

4. ABO type is a trait that is determined by multiple alleles.

5. occurs when multiple genes determine the phenotype of a trait.

6. Human eye is an example of polygenic inheritance.

D. Genes and the Environment

1. are not the only factors that can affect phenotypes.

An organism’s can also affect its phenotype.

2. The flower color of one type of hydrangea is determined by the

in which the hydrangea grows.

3. choices can affect a person’s phenotype.


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Can you infer genotype?If you know that dragon traits are either dominant or recessive, can you use phenotypes of traits to infer genotypes?

Procedure

MiniLab LESSON 2: 20 minutes

1. Select one trait card from each of three dragon trait bags. Record the data in your Science Journal.

2. Draw a picture of your dragon based on your data. Label each trait homozygousor heterozygous.

3. For each of the three traits, place one check mark in the appropriate box.

4. Combine your data with your classmates’ data.

Analyze and Conclude 1. Describe any patterns you find in the data table.

2. Determine which trait is dominant and which is recessive. Support your reasoning.

3. Determine the genotype(s) for each phenotype. Support your reasoning.

4. Key Concept Decide whether you could have correctly determined your dragon’s genotype without data from other dragons. Support your reasoning.

Dragon Traits

Phenotype Homozygous Heterozygous

Green body

Red body

Four legs

Two legs

Long wings

Short wings


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Understanding Inheritance Directions: On the line before each definition, write the letter of the term that matches it correctly. Each term is used only once.

Content Practice A LESSON 2

1. threadlike structures in cells

2. contain instructions for traits

3. two different forms of a gene

4. outward appearance

5. determines outward appearance

6. represented by uppercase letters

7. represented by lowercase letters

8. RR

9. Rr

10. shows possible outcomes of genetic crosses

11. shows inherited traits in a family

12. produces a blend of the parents’ phenotypes

13. when both alleles are expressed

14. determines human blood type

15. when multiple genes determine a phenotype

16. can sometimes influence expression of genes

A. dominance

B. pedigree

C. genotype

D. heterozygous

E. chromosomes

F. codominance

G. homozygous

H. incomplete dominance

I. genes

J. environmental factors

K. alleles

L. multiple alleles

M. recessiveness

N. polygenic inheritance

O. Punnett square

P. phenotype


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Understanding InheritanceDirections: On the line before each statement, write the letter of the correct answer.

1. Segments of chromosomes that contain coded information for an organism’s traits are called

A. cells. B. genes. C. alleles. D. genotypes.

2. The outward expression, or appearance, of a genetic trait is its A. allele. B. pedigree. C. phenotype. D. inheritance.

3. The designation Rr for a pea-plant’s peas shows that the plant is A. purple. B. a hybrid. C. homozygous. D. a true-breeding plant.

4. A model that is used to show possible outcomes of cross-breeding is a A. ratio. B. coin toss. C. pedigree. D. Punnett square.

5. A cow with red hairs and white hairs in its coat is an example of A. codominance. B. multiple alleles. C. polygenic inheritance. D. incomplete dominance.

6. Variations in people’s height and eye color are due to A. codominance. B. multiple alleles. C. polygenic inheritance. D. incomplete dominance.

Content Practice B LESSON 2


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Reader’s TheaterAn Interview with Gregor Mendel

CHARACTERS: Reporter, Gregor Mendel

Reporter: Good evening. Tonight we have a special guest in our studio. His name is Gregor Mendel. Mr. Mendel was an Austrian friar and a scientific researcher more than 150 years ago. He traveled in a time machine to get to our interview today. Thank you for coming.

Gregor Mendel: It was a long journey, but I’m glad to be here.

Reporter: Our viewers are interested to hear about how your study of peas changed the way we view heredity.

Gregor Mendel: I’m glad to hear that my work is important. I started my research in the 1850s.

Reporter: I have some questions I’d like to ask you, if you don’t mind.

Gregor Mendel: No, I don’t mind. Ask any question you’d like.

Reporter: My first question concerns your choice of plants. Why did you use pea plants?

Gregor Mendel: Pea plants grow and reproduce quickly, so I was able to breed many plants in a short period of time. Also, they have a wide variety of traits, or characteristics, so I was easily able to record the results of the cross-pollination of different varieties. I studied many generations of pea plants to reach my conclusions. My colleagues at the monastery used to grumble because we ate so many peas.

Reporter: Now I understand why you used peas. Can you describe cross-pollination?

Gregor Mendel: I transferred pollen from the flowers on certain plants to the flowers on other plants. For example, I transferred pollen from short-stemmed pea plants to other short-stemmed pea plants. I noted that the offspring from this combination were always short-stemmed, just like the parents. When I crossed tall-stemmed plants with other tall-stemmed plants, however, I noted that tall and short plants grew. To me, this meant that the short-stemmed trait must be present somewhere in the genetic makeup of the tall-stemmed pea plants.

Reporter: And for those of us who don’t have a background in genetics, what did you conclude from your experiments?

Gregor Mendel: I determined that each parent pea plant must contain two characteristics for a particular trait. When two plants with different traits, such as tall and short stems, were bred, the offspring showed only one of the traits. This was then called the dominant trait, and the trait that did not appear was called recessive.

LESSON 2Language Arts Support

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Reader’s Theater continued

Reporter: How do you think the traits are inherited?

Gregor Mendel: From the evidence I gathered in my research, I concluded that each parent contributes one factor to the plant in the offspring generation. So, the offspring in the first filial generation gets one factor from the female parent and one factor from the male parent. The two factors interact to produce the resulting trait.

Reporter: Why is this called the study of heredity? What was it about your experiments that changed the way we look at heredity today?

Gregor Mendel: Until the time I conducted my research, people believed that the blending of traits resulted when two complex life-forms such as plants reproduced. I disproved that hypothesis by crossing two different flower colors, for example. I never saw a mixture of purplish-white flowers on a plant. The result was always purple or white.

Reporter: Can you give us an example with humans?

Gregor Mendel: Sure. Some people have unattached earlobes; that is, a part of the lobe hangs down from the side of the head. This is a dominant trait. The recessive trait is an attached earlobe. The lower part of this type of earlobe attaches directly to the side of the head. If a person’s mother has attached earlobes and the father has unattached earlobes, then the person will have attached or unattached earlobes, but not something in between. Not all traits follow such simple patterns of inheritance, but some do.

Reporter: Well, we hope you are aware that your work is important to the scientific community, although not everyone recognized your findings during your time. By 1900 your work was recognized as important to the world of biology, specifically to the study of genetics. Thanks again for your time this evening. We are fortunate to have had this opportunity to speak with you, Mr. Mendel. Have a pleasant trip back through history.

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School to Home LESSON 2

Understanding InheritanceFor this activity, you will need the tables below and a pencil. Refer to your textbook as needed.

A farmer who raises vegetables wants to cross two types of corn plants. One type is a homozygous plant with red kernels (RR) and the other is a homozygous plant with white kernels (rr). For these plants, red color is dominant and white color is recessive. Fill in the Punnett square below to predict the offspring the farmer should expect.

1. Using the Punnett square, predict the color of the corn kernels. Will the plants produce all red kernels, all white kernels, or a mixture of both colors?

2. What would be the ratio of red corn to white corn in the offspring?

Next, the farmer cross-pollinates the red hybrid (Rr) offspring. Complete the Punnett square below for this cross.

3. Using the Punnett square, predict the color of the corn kernels. Will the plants produce all red kernels, all white kernels, or a mixture of both colors?

4. What would be the ratio of plants with red kernels to plants with white kernels in the offspring?

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Understanding InheritanceKey Concept What determines the expression of traits?

Directions: On each line, write the term from the word bank that correctly completes each sentence. Some terms may be used more than once.

alleles chromosomes dominant genes genotype

heterozygous homozygous phenotype recessive

1. An organism’s are located on threadlike structures

called .

2. The different forms of are called .

3. A trait’s is its observable expression in the organism.

4. The observable expression of a trait is determined by its .

5. When an organism has two for a certain trait that are the

same, the of that trait is said to

be .

6. When the two are different, the

is said to be .

7. The genotype Rr results in a round pea, because the round

pea allele is to the wrinkled pea allele.

8. The wrinkled pea phenotype is and has the

genotype rr.

Key Concept Builder LESSON 2

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Understanding InheritanceKey Concept What determines the expression of traits?

Directions: The ozmox is a fictional creature with a variety of traits. Study the list of ozmox alleles for the seven traits below. Then look at the genotypes of a particular ozmox named Glork. Using that information, write Glork’s phenotype for each trait on the lines provided.

Ozmox alleles:Hair—shaggy (S); short-haired (s)Nose—orange (O); green (o)Tail—long (L); stubby (l)Teeth—pointed (P); rounded (p)Claws—curved (C); straight (c)Eyes—red (R); blue (r)Ears—big (B); small (b)

Glork’s genotypes: Ss, oo, LL, Pp, cc, rr, BB

1. Hair:

2. Nose:

3. Tail:

4. Teeth:

5. Claws:

6. Eyes:

7. Ears:



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Understanding InheritanceKey Concept How can inheritance be modeled?

A Punnett square is a model used to predict the possible outcomes of genetic crosses between organisms when their genotypes are known.

Directions: Complete the Punnett squares below.

1. Show a first-generation cross between two true-breeding pea plants—one with purple flowers (genotype PP) and one with white flowers (genotype pp).

2. Show a second-generation (hybrid) cross between two of the plants from the first-generation cross.

Directions: Answer each question on the lines provided.

3. What percentage of the offspring from the first-generation cross is likely to have purple

flowers? White flowers?

4. What percentage of the offspring from the second-generation cross is likely to have

purple flowers? White flowers?

5. What is the chance, in the form of a ratio, that the offspring from the second-

generation cross have purple flowers?

6. What is a pedigree?


P P

p

p

P p

p

p


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Understanding InheritanceKey Concept How do some patterns of inheritance differ from Mendel’s model?

Directions: Complete this spider map with information about the four kinds of complex patterns of inheritance discussed in the lesson. On each top line, list one of the patterns. On each bottom line, give an example of a trait produced by that type of inheritance.

Directions: Answer each question on the lines provided.

5. What are three environmental factors that can influence plant phenotypes?

6. What causes a Siamese cat to have dark fur on some parts of its body?

7. Which factor determines the wing pattern and coloration of the map butterfly?

Complex Patterns of Inheritance

1. 2.

3. 4.


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In Colorado, the potato beetle plagued potato crops for years. Potato beetles would eat an entire field, leaving nothing but stems.

In the past, farmers used chemical pesticides to control the beetle. But pesticides can contaminate soil and water. Some pesticides are linked to cancer. Farmers were left with a difficult choice—use chemicals that could potentially pollute the land or let the beetle destroy the potato crop.

Fortunately, scientists gave farmers a third option—a “smarter” potato that could fend off the beetle on its own.

Gene ModificationResearchers developed the disease-

resistant potato using gene modification. Gene modification is a type of biotechnology that is used to improve plants, animals, and microorganisms. In the case of the potato, researchers inserted a gene that changed the DNA of the potato. The potato now contains an organic pesticide, or biopesticide, that is deadly to the beetle.

Approximately 56 million hectares of American farmland are planted with genetically modified (GM) crops. Use of the technology is increasing in certain Asian,

African, and Latin American countries where hunger and malnutrition are epidemic. Scientists are focusing on developing GM crops that are more nutritious and more disease-resistant. For example, researchers have developed a rice plant that contains iron and vitamin A, and a genetically altered sweet potato that resists a destructive virus.

Concerns over GM CropsGM crops hold much promise for

reducing malnutrition and starvation. However, their use raises several concerns. The genes of GM plants might cross-fertilize with wild plants and create “superweeds.” These superweeds could become resistant to herbicides and compete with food crops for limited space. In addition, pests targeted by disease-resistant GM crops might mutate and become even more difficult to control.

There are also concerns for human safety. Opponents fear that allergies and other illnesses could result from eating GM crops. They point out that scientists likely do not know all the potential effects of these crops on humans and the environment. Already, studies indicate that the pollen from one variety of GM corn kills the caterpillar Danaus plexippus, the larva of the monarch butterfly.

GM Crops

LESSON 2Enrichment

Applying Critical-Thinking SkillsDirections: Answer each question.

1. Summarize What problems prompted scientists to begin developing GM crops?

2. Evaluate Do you think the use of GM crops should be expanded? Why?

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LESSON 2Challenge

Analyze a Punnett Square for Two Traits In peas, round shape (R) is dominant over wrinkled shape (r), and yellow color (Y) is

dominant over green (y). Suppose that a pea plant that has genotype RrYy is crossed with a pea plant that has genotype rrYy. Fill in the Punnett square below to predict the possible phenotypes and genotypes of the offspring. Then analyze the Punnett square. How many different phenotypes and genotypes are possible?

RY Ry rY ry

rY

ry

rY

ry

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How can you use Punnett squares to model inheritance? Geneticists use models to explain how traits are inherited from one generation to the next. A simple model of Mendelian inheritance is a Punnett square. A Punnett square is a model of reproduction between two parents and the possible genotypes and phenotypes of the resulting offspring. It also models the probability that each genotype will occur.

Learn ItIn science, a model is a representation of how something in the natural world works. A model is used to explain or predict a natural process. Maps, diagrams, three-dimensional representations, and mathematical formulas can be used to help model nature.

Try It 1. Use the Punnett square on this page to complete a

cross between a fruit fly with straight wings (cc) and a fruit fly with curly wings (CC).

2. According to your Punnett square, which genotypes are possible in the offspring?

3. Using the information in your Punnett square, calculate the ratio of the dominant phenotype to the recessive phenotype in the offspring.

Apply It 4. Based on the information in your Punnett square, how many offspring will have curly

wings? Straight wings?

5. If you switch the locations of the parent genotypes around the Punnett square, does it affect the potential genotypes of their offspring? Explain.

6. Key Concept Design and complete a Punnett square to model a cross between two fruit flies that are heterozygous for curly wings (Cc). What are the phenotypic ratios of the offspring?

ModelSkill Practice LESSON 2: 25 minutes

C Cc Cc

c

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Lesson 2 | Understanding Inheritance