OwlSheets Students
← Exit

A Missing Muscle Protein: Sprinters, Volunteers and Lab Mice

0 / 11

A Missing Muscle Protein: Sprinters, Volunteers and Lab Mice

Trace one common gene change from DNA to protein to traits.

Part 1: Gene, protein and sprint data

Read the passage and Table 1. In Table 1, a difference of less than 0.05 s in sprint time or less than 2 cm in jump height is normal variation and does not count as an effect.

The Question After the Physical

1Jalen Torvik runs the 100 m dash for his middle school track team. At his preseason physical, the sports medicine doctor, Dr. Marisa Quenneville, checked his heart, lungs and joints and cleared him to compete. Jalen had a question for her. A teammate had read online that some people are "born without a sprint gene." Was that true?

2Dr. Quenneville explained that muscles contain two main kinds of fibers. Slow fibers keep working for a long time without tiring, which helps in long runs. Fast fibers contract quickly and powerfully, which helps in sprints and jumps, but they tire sooner. Inside fast fibers is a protein called alpha-actinin-3. It helps hold the fiber's strands of protein in place while the fiber pulls hard. Like every protein, it is built from instructions in a gene.

3Each person carries two copies of this gene, one from each parent. The typical version, called R here, holds the full instructions. A common version, called X, has a single changed letter in its DNA. Because of that change, the cell stops building the protein partway through, and the short piece is broken down. A person with two copies of version X makes no alpha-actinin-3 at all. In some groups of people, about one person in five has two X copies, and these people are healthy. A related protein, built from a different gene, does a similar job in their fast fibers.

4Dr. Quenneville showed Jalen results from a sports science lab. The lab tested 120 adult volunteers who all trained with the same running club for a year. Each volunteer ran a timed 30 m sprint and did a standing jump test. The lab also checked each volunteer's gene versions and looked at a tiny sample of fast fibers under a microscope (Table 1). Every volunteer gave permission, and each test was run three times, with the best result kept.

5The same lab bred mice that lack alpha-actinin-3 and compared them with typical mice of the same age and size. Each mouse ran on a slow treadmill until it tired, and a grip test measured how hard its front paws could pull (Table 2).

Table 1: Running Club Volunteers (group averages)
Gene versionsVolunteersAlpha-actinin-330 m sprint (s)Standing jump (cm)
R and R40Normal amount4.6246
R and X50Less, still present4.6545
X and X30None4.8141
1.
Use paragraphs 2 and 3 and Table 1. Sort each statement by the level it describes.
2.
Use Table 1. Compare the R and R group with the X and X group.

On average, the X and X volunteers took s longer to run 30 m.

3.
Use Table 1 and the rule above it. What do the results for the R and X group suggest?
Question 3 options
4.
People with two X copies make no alpha-actinin-3, yet they are healthy. Which explanation fits paragraph 3 best?
Question 4 options
5.
Based on Table 1, how does having two X copies most likely affect a person in a 100 m sprint race?
Question 5 options

Part 2: Mice, training and the whole picture

Use paragraph 5, Table 2 and what you found in Part 1.

Table 2: Lab Mice (averages of 20 mice in each group)
MiceAlpha-actinin-3Treadmill run (m)Front-paw grip (N)
TypicalNormal amount1,2001.8
Bred to lack itNone1,6001.6
6.
Use Table 2. Compare the treadmill runs of the two groups of mice.

To the nearest whole percent, the mice that lack the protein ran % farther than the typical mice.

7.
Circle the two results that are evidence that the missing protein lowers muscle strength or power.

8.
Which conclusion do Table 1 and Table 2 support together?
Question 8 options
9.
Jalen has an R copy and an X copy. Over eight weeks of hard sprint training, his 30 m time drops from 4.80 s to 4.70 s. What most likely happened?
Question 9 options
10.
Use Table 1.

Of the 120 volunteers, % had two X copies.

11.
Jalen's teammate says, "Version X is a harmful mutation. Anyone who has two X copies is worse off." Do you agree? Write a claim, give evidence from both tables and the passage, and explain your reasoning step by step from the gene to the protein to the trait.