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Day 3 · Topic 3 of 6

Genetics

DNA structure, Punnett squares, protein synthesis, mutations, inheritance patterns, and genetic engineering.
📝 10 Questions ⏱ ~45 min ✅ answers-topic3.html

🐱 Cat Genetics Fun Fact!

Alishba, did you know that calico cats are almost always female? The orange and black coat colours are carried on the X chromosome — so a cat needs TWO X chromosomes (XX) to display both colours. Male cats (XY) almost never have both. This is the same sex-linked inheritance you will study in Question 8! Every calico cat is a walking genetics lesson.

✏️ Worked Example — Read This First!

Two heterozygous tall pea plants (Tt × Tt) are crossed. Draw the Punnett square and give the genotypic and phenotypic ratios.
1
Set up the Punnett square.
Parent 1 gametes: T and t. Parent 2 gametes: T and t.
2
Fill in the boxes.
TT | Tt | Tt | tt
3
Genotypic ratio.
1 TT : 2 Tt : 1 tt (1 homozygous dominant : 2 heterozygous : 1 homozygous recessive).
4
Phenotypic ratio.
Since T (tall) is dominant over t (short): 3 tall : 1 short. That means 75% tall, 25% short.
Genotypic ratio: 1 TT : 2 Tt : 1 tt. Phenotypic ratio: 3 tall : 1 short.
💡 Memory trick: For a monohybrid cross of two heterozygous parents, the phenotypic ratio is ALWAYS 3:1. Write this on your reference sheet!
Easy
Questions 1–3
Question 1 EasySee Answer →
Define the following terms: gene, allele, genotype, phenotype, dominant, recessive, homozygous, heterozygous.
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Question 2 EasySee Answer →
In pea plants, round seeds (R) are dominant over wrinkled seeds (r). Cross Rr × Rr. Draw the Punnett square and give the genotypic and phenotypic ratios.
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Question 3 EasySee Answer →
What is the difference between mitosis and meiosis? Which type of cell division produces gametes? How many chromosomes does a human egg cell have?
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Medium
Questions 4–7
Question 4 MediumSee Answer →
What is DNA? Describe its double helix structure. Name the four bases and explain the base pairing rules (A-T, G-C).
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Question 5 MediumSee Answer →
Describe the process of protein synthesis in TWO stages: transcription and translation. Where does each occur? What is the role of mRNA, tRNA, and ribosomes?
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Question 6 MediumSee Answer →
What is a mutation? Describe the difference between a point mutation (substitution) and a frameshift mutation (insertion/deletion). Give one example of a disease caused by each type.
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Question 7 MediumSee Answer →
Explain incomplete dominance and codominance with one example of each. How do these differ from simple dominant/recessive inheritance?
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Hard
Questions 8–10
Question 8 HardSee Answer →
A woman is a carrier for colour blindness (XBXb). She has children with a man who has normal vision (XBY). a) Draw the Punnett square. b) What is the probability of a colour-blind son? c) A colour-blind daughter? d) Why is colour blindness more common in males?
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Question 9 HardSee Answer →
What is genetic engineering? Describe the steps used to insert a human insulin gene into a bacterial cell. What is the role of restriction enzymes and plasmids? Why is this medically important?
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Question 10 HardSee Answer →
Compare the following chromosomal abnormalities: Down syndrome (trisomy 21), Turner syndrome (45, X0), Klinefelter syndrome (47, XXY). For each: a) cause (what went wrong in meiosis), b) chromosome number, c) main characteristics.
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🌟 Great work, Alishba!

You have just unlocked the code of life! DNA is like the sheet music for a Vocaloid song — the sequence of notes (bases) determines the melody (protein). Just as Len Kagamine’s voice is synthesised from digital code, your body is built from the genetic code in your DNA. Tomorrow: Evolution!