Grade 9 Science Worksheets
Inside nearly every cell of your body is a 2-meter-long instruction manual written in a 4-letter alphabet. It's the reason you have your grandmother's eyes.
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What your child will learn: Biology: DNA & Genetics
- DNA is a double helix: a twisted ladder whose rungs are base pairs, A pairs with T, C pairs with G.
- A gene is a section of DNA that codes for a trait. Humans have about 20,000 genes on 46 chromosomes (23 from each parent).
- Dominant alleles (B) mask recessive ones (b). Two brown-eye-gene parents can have a blue-eyed child if both carry a hidden 'b'.
- Punnett squares predict trait probability: cross Bb × Bb and there's a 1-in-4 chance of bb (recessive trait shows).
Sample worksheet questions
1. How many chromosomes do humans have, and from where?
Answer: 46, 23 from each parent
2. What is a gene?
Answer: A section of DNA that codes for a trait
3. In a Bb × Bb cross, what fraction of offspring show the recessive trait?
Answer: 1/4 (the bb combination)
4. In genetics, what does a capital letter like 'B' represent?
Answer: A dominant allele
5. Why can two brown-eyed parents have a blue-eyed child?
Answer: Both can carry a hidden recessive allele and each pass it on
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🧬 Family Trait Tracker: Survey your family for tongue-rolling, ear lobe attachment, and hand-clasping preference. Chart which traits appear in which generations!
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