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This page shows questions in the Flatfish public release module at MSDE. Life Science MISA
"Flatfish"

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Flatfish

The summer flounder is an important commercial and recreational fish found in the Chesapeake Bay. It is part of a group of vertebrates called flatfish that are found throughout the world. The most obvious characteristic of the flatfish is its asymmetry. Each side of the flatfish, when divided by a central line, is not identical.

Flatfish are born as symmetrical larvae swimming upright; however, as the flatfish develop into juveniles, they undergo many body changes during a process called metamorphosis. One significant change is the migration of one eye from one side of the head to the other. An adult flatfish has both eyes on the same side of its head. Adult flatfish usually lay flat on the ocean floor with both eyes on the upward-facing side of the head. Another change is in the coloration on the side of the body facing upward; it darkens to match the ocean floor. Adult flatfish swim with a sideways flapping motion. A diagram of an adult flatfish is shown.

The picture shows an adult Flatfish with both eyes on the same side of the head.

Eye migration in flatfish is controlled in part by the hormone thyroxine, produced by the thyroid gland. Thyroxine is produced by all vertebrates, but it causes eye migration only in flatfish. Thyroxine binds to molecules called thyroid receptors on the nuclear membrane of a cell and enters the nucleus of the cell. In the nucleus, it activates specific genes. The model shows what happens when thyroxine binds to its receptor.

The diagram titled Cell Response to Thyroxine shows parts of a cell. The cell membrane, Cytoplasm, Nuclear membrane and Nucleus are labeled. A Thyroxine hormone molecule starts outside the cell and passes through the cell membrane, where it connects with a Thyroxine receptor, then passes through the Nuclear membrane, where it connects with a Gene.

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Thyroxine Hormone

Scientists have extensively studied the metamorphosis in flatfish to understand the way in which thyroxine influences this process. The graphs show the relationship between thyroxine levels and the levels of gene expression during the flatfish larval stage. The migration of the eye occurs between day 25 and day 40. The coloration change in the upper side of the body occurs between day 40 and day 47. At day 47 metamorphosis is complete and the flatfish is now a juvenile.

The first graph is titled Thyroxine Hormone Level. The x axis is labeled Age of Fish in days. The x axis begins at zero and ends at fifty, increasing by intervals of ten. The y axis is labeled Thyroxine Level. The y axis begins at Low and ends at High. The data line starts at zero, medium-low, then decreases rapidly until it reaches three, very low, and stays about the same until it reaches twenty-five, low, where it begins to increase slowly to thirty-four, low, where it rises rapidly to thirty-five, medium-high, then dips slightly to thirty-nine, medium. The line then increases rapidly to forty, very high, then decreases rapidly to the end at forty-eight, medium. The second graph is titled Cellular Response to Thyroxine. The x axis is labeled Age of Fish in days. The x axis begins at zero and ends at fifty, increasing by intervals of ten. The y axis is labeled Level of Gene Expression. The y axis begins at Low and ends at High. The data line starts at zero, lowest, then increases rapidly until it reaches twelve, medium, where it begins to fluctuate slowly down and up, reaching sixteen, medium-low, then thirty-one, low. The line then increases rapidly to forty, high, and decreases rapidly to the end at forty-nine, medium-low.

The diagrams shows the physical changes flatfish undergo during metamorphosis.

There is a table titled Flatfish Metamorphosis. The table has four columns and three rows. The first column heading is Age in Days. The second column heading is Eye Migration. The third column heading is Swimming Position. The fourth column heading is Body Form. The key shows that the black dot represents the Migrating eye and the gray dot represents the Non-migrating eye. The first row is twenty-one, picture showing the migrating eye in almost the same location as the non-migrating eye on opposite sides of the head, picture showing the body tilted slightly to one side, picture showing the body parts developing and not clearly defined. The second row is thirty, picture showing the migrating eye on same side of the head as the non-migrating eye, picture showing body tilted to forty-five degree angle, picture showing the body parts defined, elongated, and flattened. The third row is fifty, picture showing the eyes unchanged, picture showing the body tilted to ninety degrees, picture showing the body fully developed.

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History of Flatfish

Scientists studied fossils from 50 million years ago to determine if there were transitional forms between symmetrical fish and asymmetrical flatfish. Transitional forms would have traits common to both ancestral fish and present-day flatfish. The phylogenetic tree shows the relationship between living flatfishes (Fishes C and D), a symmetrical fish (Fish A), and an extinct transitional form (Fish B) that was discovered.

The diagram titled Phylogenetic Tree shows the branching lines connecting four different fish. The key shows that the black dot represents the Migrating eye and the gray dot represents the Non-migrating eye. Fish A branches first from the source line, followed by Fish B, then Fish C and Fish D which are a branching pair.

Scientists compared certain genes in the symmetric fish and the flatfish. They compared these genes in symmetric stickleback, puffer fish, and zebra fish to two species of flatfish. A portion of the data from the scientific study are shown.

There is a table titled Amino Acid Differences. The table has three columns and five rows. The first column heading is Fish Species. The second column heading is Amino Acid Positions two hundred fifty-five through two hundred fifty-eight. The third column heading is Amino Acid Positions three hundred thirty-four through three hundred thirty-seven. The key shows that capital A represents Alanine, capital E represents Glutamate, capital H represents Histidine, capital L represents Leucine, capital P represents Proline, capital R represents Arginine, capital S represents Serine, capital T represents Threonine, capital Y represents Tyrosine. The first row is Stickleback, capital R H A E, capital A P L T. The second row is Pufferfish, capital R H A E, capital A P L T. The third row is Zebrafish, capital R H V E, capital S P L T. The fourth row is Japanese flouder (flatfish), capital R Y A E, capital A P L S. The fifth row is Tongue sole (flatfish), capital R Y A E, capital A P L S.

This is a drag and drop question that allows you to select text and place it in an appropriate answer space.

Create a sequence to show what happens when the thyroxine hormone activates a gene. Select and drag the processes into the correct positions.

The eye migration protein is created. DNA is transcribed into mRNA. The hormone and receptor bind to the gene. The amino acid sequence is created.

Arrow pointing down.

Arrow pointing down.

Arrow pointing down.

This is a test question that allows you to select a spot or region on a graphic.

The Phylogenetic Tree diagram can be used to show relatedness. Select the two fishes that are most closely related to each other.

This is a test question that allows you to enter extended text in your response.

Describe evidence that supports a relationship between biological evolution and the common ancestry of flatfish.

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