The Shelter Litter Notebook
A fifth-grade class volunteers at a local animal shelter and records data on a litter of six puppies. The mother is a black Labrador retriever with floppy ears and webbed feet. The father is not known. In their notebooks, the students list: three puppies have black coats, two are yellow, and one is chocolate brown; all six have floppy ears and webbed feet; one puppy has a white patch on its chest; one puppy has a notch in its left ear from catching it on a fence; and by week eight, four puppies sit on command after training while two still need practice. A visitor tells the class that the brown puppy will pass its brown coat to its own puppies, but that the puppy with the notched ear will pass the notch on too. The class must sort the traits and explain their reasoning to the visitor.
1. Sort the listed traits into inherited traits and acquired traits, and explain the rule you used for each group.
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Inherited traits - passed from parents through genes: coat color (black, yellow, brown), floppy ears, webbed feet, and the white chest patch. These are physical features the puppies were born with, and they came from the mother's and father's genetic material. The variation in coat color shows the father contributed different color information than the mother.
Acquired traits - gained during life: the notched left ear, and sitting on command. The notch is an injury from a fence, and sitting is a learned behavior from training. Neither is coded in the puppies' genes.
The rule: an inherited trait is present at birth and comes from parents; an acquired trait is gained by experience, injury, learning, or environment. A quick test is to ask, 'Was this puppy born with it, and could it have come from the parents' bodies?'
2. Respond to the visitor's two claims. Which one is correct and which is not, and why?
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The visitor is correct about the brown coat and wrong about the notched ear.
Coat color is inherited. Each puppy received gene instructions from both parents, and those instructions control pigment. So the brown puppy can pass brown-coat instructions to its own puppies. Because the father's traits are unknown, the class cannot say for sure what the puppies of a future litter will look like - but the potential to pass on coat color is real.
The notch is an acquired trait caused by a fence, a change to the body that did not alter the dog's genes. Nothing about a scar or injury can be written into the instructions a puppy passes on, in the same way a person's broken arm is not passed to their children. The same reasoning applies to sitting on command: a trained behavior is learned, not inherited.
3. The class must also classify the puppies in a report. State the vertebrate group the puppies belong to, give two pieces of evidence from the notebook, and explain why the litter has different coat colors.
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Vertebrate group: mammals. Evidence from the notebook: the puppies have fur (their coats) and were born from a mother that fed and cared for them - live birth and milk are mammalian features. They also breathe with lungs and have a backbone, which is what makes them vertebrates.
The differing coat colors within one litter come from inherited variation. Each puppy received a different mix of gene instructions from the mother and the unknown father. The mother carries black coat information, while the father's coat color is unknown; some puppies received instructions for yellow or chocolate. Same parents, different combinations - which is why littermates are not identical.
The notch and the sitting behavior should be left out of the inherited-trait section of the report, though the class may note that trained behavior is an acquired trait that can be influenced by environment and practice.