Genetics
- Monohybrid cross (Aa × Aa)
- genotypes 1 : 2 : 1, phenotypes 3 : 1
- Dihybrid cross
- phenotypes 9 : 3 : 3 : 1
- Hardy–Weinberg
- p + q = 1, p² + 2pq + q² = 1
- Independent genes
- multiply the probabilities
Biology: Genetics and Cell Biology: cram pack
Formula sheets, the key method steps for every topic and 4 practice problems, with full solutions at the back.
1Formulas and methods
2Practice problems
1.GeneticsMedium
Duchenne muscular dystrophy is X-linked recessive (allele d). A carrier mother, XDXd, has children with an unaffected father, XDY. The mother's gametes run down the side. Click the cell for an affected son.
♀ XDXd♂ XDY
- 1Xd × XD
- 2Xd × Y
- 3XD × XD
- 4XD × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives round seeds (dominant) or wrinkled seeds; gene B gives yellow seeds (dominant) or green seeds. Click the one cell for an offspring that is shows both wrinkled seeds and green seeds.
AaBb × AaBb
- 1ab × AB
- 2ab × ab
- 3ab × Ab
- 4ab × aB
- 5aB × AB
- 6aB × ab
- 7aB × Ab
- 8aB × aB
- 9AB × AB
- 10AB × ab
- 11AB × Ab
- 12AB × aB
- 13Ab × AB
- 14Ab × ab
- 15Ab × Ab
- 16Ab × aB
3.Cell biologyMedium
Which enzyme unwinds the DNA double helix during replication?
- APrimase
- BHelicase
- CDNA polymerase
- DDNA ligase
4.Cell biologyHard
Which statement about the sodium–potassium pump is correct?
- AIt moves Na⁺ and K⁺ in the same direction across the membrane
- BIt needs no energy
- CIt moves 2 Na⁺ out and 3 K⁺ in
- DIt moves 3 Na⁺ out and 2 K⁺ in for each ATP used
3Solutions
1.Genetics
Answer: Xd × Y
Punnett square: one parent's gametes run along the top, the other's down the side. Each cell joins the gamete above it with the gamete beside it, and every cell is equally likely. A recessive trait only shows when both alleles are recessive; for an X-linked trait, sons get their only X from the mother.
Fill the square
XdXD, XdY, XDXD, XDY
Find the cell
Xd × Y = XdY
Answer
Cell Xd × Y → XdY
2.Genetics
Answer: ab × ab
Punnett square: one parent's gametes run along the top, the other's down the side. Each cell joins the gamete above it with the gamete beside it, and every cell is equally likely. A recessive trait only shows when both alleles are recessive; for an X-linked trait, sons get their only X from the mother.
Genotype asked for
aabb
Gametes
A homozygous genotype needs the same gamete from both parents, so only one cell in the 16 fits.
ab × ab = aabb
Answer
Cell ab × ab → aabb
3.Cell biology
Answer: B · Helicase
Why this is the answer
Helicase separates strands at the replication fork; primase lays primers, polymerase extends them and ligase joins fragments.
Answer
B · Helicase
4.Cell biology
Answer: D · It moves 3 Na⁺ out and 2 K⁺ in for each ATP used
Why this is the answer
The Na⁺/K⁺-ATPase exports 3 Na⁺ and imports 2 K⁺ per ATP, maintaining gradients and contributing to the resting potential.
Answer
D · It moves 3 Na⁺ out and 2 K⁺ in for each ATP used
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