Worksheet

Pale Stripes, Weak Muscles and a River Fish: Gene Changes at the Research Station

Grade 8 gene mutation practice: zebrafish lab lines and a river fish's pollution test show changed proteins with harmful, helpful or neutral effects.

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11 questions
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Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Short answer

About this worksheet

What students practice

Students trace how a gene mutation changes a protein and then a trait of an organism.
Students use data to decide whether a mutation is harmful, helpful or neutral in a given setting.
Students explain why the same mutation can help in one environment and make little difference in another.

How to use

Review the gene, protein and trait model in paragraph 2 before students start. The tables are averages, so remind students to compare groups rather than single fish.

Curriculum

NGSS standard covered

MS-LS3-1

Explain how gene mutations can change proteins and have harmful, helpful or neutral effects on an organism.

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Pale Stripes, Weak Muscles and a River Fish: Gene Changes at the Research Station

Follow three gene changes from the protein to the trait and decide how each one affects the fish.

Part 1: Two zebrafish lines

Read the station notes, then use them and Tables 1 and 2 to answer the questions.

A Week at the River Research Station

1Imani Castellano, an eighth grader, spent a week of her summer in a youth program at a river research station on the Hudson River in New York. The station studies wild fish from the river, and it also keeps tanks of zebrafish, small striped fish that scientists use to study genes. Zebrafish breed quickly, and their young larvae are nearly see-through, so their muscles and organs can be watched under a microscope.

2The station's geneticist, Dr. Leopold Nakashima, began with a model. A gene is a section of DNA on a chromosome that holds the instructions for making a protein. Proteins do many jobs in cells: some help build pigment, some hold muscle together and some receive chemical signals. A mutation is a change in a gene. If the change alters the shape of the protein, the protein may work differently or not at all, and a trait of the organism may change. Some mutations leave the protein's shape and job the same.

3The first zebrafish line Imani studied was the golden line. These fish carry a mutation in a gene for a protein in pigment cells that is needed to build dark pigment grains. In golden fish the protein is changed, and their pigment grains are fewer, smaller and paler than usual.

4The second line was the sapje line. These fish carry a mutation in the gene for a large muscle protein that holds the ends of each muscle fiber firmly to the tissue around it. Sapje fish make none of this protein. Imani tapped the side of each larva's dish and filmed how far it darted, then looked at its muscles under a microscope.

5The last fish was not from the lab. Atlantic tomcod live in the Hudson, where the mud still holds PCBs, pollutants released by factories decades ago. In young fish, PCBs attach to a receptor protein inside cells. The receptor then switches on genes that can cause heart and jaw deformities. Most Hudson tomcod carry a version of the receptor gene with a small piece missing, so their receptor protein lacks two of its building blocks and holds on to PCBs much less tightly. Dr. Nakashima showed Imani results from a lab test like ones scientists have run with tomcod from the Hudson and from a clean river.

Table 1: Zebrafish Larvae at 5 Days Old (averages of 30 larvae per line)
Line	Stripes	Damaged muscle (%)	Dart after a tap (mm)
Usual (no mutation)	Dark blue	2	22
Golden	Pale	2	21
Sapje	Dark blue	96	8

Table 2: Adult Zebrafish at 4 Months in the Lab Tanks (averages)
Line	Body length (cm)	Eggs per spawning	Survived to 4 months (%)
Usual (no mutation)	3.1	210	85
Golden	3.1	205	84

Use paragraphs 2 and 3. Which chain best explains how the golden mutation leads to pale stripes?

A. The pigment grains shrink → the gene breaks apart → the muscle protein is lost → the stripes look pale
B. The gene changes → the pigment-cell protein changes → fewer and paler pigment grains form → the stripes look pale
C. The fish lives in pale water → its pigment cells copy the water color → the pigment gene changes
D. The stripes fade → the pigment-cell protein changes → the gene changes to match the new stripes

Use Table 1. Compare the sapje larvae with the usual larvae.

On average, the sapje larvae darted mm less after a tap.

Use paragraph 4 and Table 1. Which explanation of the sapje results fits the evidence best?

A. Without the anchoring protein, muscle fibers are damaged as larvae move, so they dart weakly.
B. Sapje larvae were tapped more gently, so they darted shorter distances than the others.
C. Sapje larvae have pale stripes, so they are easier to see and dart less to save energy.
D. Sapje larvae make extra muscle protein, so their muscles are too stiff to dart far.

Use Tables 1 and 2. In the lab tanks, how does the golden mutation most likely affect the fish?

A. It lowers survival to 4 months by about a third, so it is harmful there.
B. It weakens the muscles, so golden larvae dart much less far than the usual larvae.
C. It makes golden adults grow longer and lay more eggs, so it is helpful there.
D. It changes the stripes but has about no effect on growth, survival or eggs, so it is about neutral there.

Circle the two results that are evidence that the golden mutation changes the color of the fish.

Golden larvae have pale stripes, while usual larvae have dark blue stripes.Golden adults lay about 205 eggs per spawning.Golden pigment grains are fewer, smaller and paler than usual.Golden adults grow to an average length of 3.1 cm.Golden larvae dart about 21 mm after a tap.

Suppose the station finds a new zebrafish with a mutation in the golden gene at a different spot. Tests show that its pigment-cell protein has the usual shape and works as usual. Based on paragraph 2, what stripes would you predict?

A. Dark blue stripes, because the protein that builds pigment still works
B. Damaged muscles, because a mutation in one gene changes many proteins
C. Stripes paler than golden fish, because it has a second mutation
D. Pale stripes, because the fish has a mutation in the golden gene

Part 2: Tomcod and PCBs

Use paragraph 5 and Table 3 to answer the questions.

Table 3: Young Tomcod With Heart or Jaw Deformities (100 larvae in each group)
Where parents lived	Receptor gene	Water	Larvae with deformities
Clean river	Usual	No PCBs	3
Clean river	Usual	Small amount of PCBs	74
Hudson River	Piece missing	No PCBs	4
Hudson River	Piece missing	Small amount of PCBs	6

Use Table 3. Compare the two groups raised in water with a small amount of PCBs.

In the PCB water, more larvae with the usual receptor gene had deformities than larvae with the changed gene.

Use paragraph 5 and Table 3. Why did so few Hudson larvae have deformities in the PCB water?

A. Their parents lived with PCBs, so the larvae learned to stay away from the PCBs in the water.
B. Their changed receptor protein holds PCBs less tightly, so it switches on the harmful genes much less.
C. Their receptor gene makes extra receptor protein, so it soaks up PCBs before they reach the heart.
D. The PCBs changed their receptor gene during the test, so the larvae grew resistant within days.

Look only at the two groups raised in water with no PCBs. What do these rows suggest about the tomcod receptor mutation?

A. It is harmful in clean water, because 4 larvae had deformities instead of 3.
B. It is helpful in clean water, because the Hudson larvae grew faster.
C. It is about neutral in clean water, because both groups had about the same few deformities.
D. It turns harmful in clean water, because the receptor then holds PCBs more tightly.

10.

Use all three tables. Fill in each blank with a word from the word bank. Each word is used once.

Word bank: harmful · helpful · neutral

For a young tomcod in water with PCBs, the receptor mutation is . For a sapje larva in a lab tank, the muscle protein mutation is . For a golden fish in a lab tank, the pigment mutation is about .

11.

Explain how the same receptor mutation can help a young tomcod in the Hudson River but make almost no difference to a young tomcod in clean water. Write a claim, give evidence from Table 3, and explain your reasoning step by step from the gene to the protein to the trait.