Many Genes, One Height: teacher key

How You Grow, grade 9 edition, written for 9th grade. Height comes from many genes working together. Bones lengthen at growth plates, where layers of cells build new bone until the plates close.

Read the book. Print this page for the key.

Questions and answers

1. Where does a long bone grow longer?
   • From its middle outward
   • Only at the joints
   • At each end, next to a growth plate (answer)
2. What does polygenic mean in the phrase polygenic trait?
   • Shaped by a single gene
   • Shaped by many genes working together (answer)
   • Shaped only by food
3. About how much of the differences in height between people do studies suggest are decided by the heights of their parents?
   • 60% to 70% (answer)
   • 30% to 40%
   • 90% to 100%
4. What happens to cartilage in a growth plate as the bone lengthens?
   • It stays the same forever
   • It is replaced by bone (answer)
   • It turns into muscle
5. Why does a bone stop getting longer after a growth plate has closed?
   • The plate has hardened into solid bone (answer)
   • The cartilage at the joint has grown larger
   • The bone has stopped being living tissue

Words

• polygenic: from many genes
• cartilage: rubbery tissue
• hypertrophic: swollen large
• epiphysis: bone end