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
red-green colour blindness is X-linked recessive (allele b). A carrier mother, XBXb, has children with an affected father, XbY. The mother's gametes run down the side. Click the cell for an affected daughter.
♀ XBXb♂ XbY
- 1XB × Y
- 2XB × Xb
- 3Xb × Y
- 4Xb × Xb
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives purple flowers (dominant) or white flowers; gene B gives black fur (dominant) or white fur. Click the one cell for an offspring that is shows both white flowers and white fur.
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 motor protein generally carries cargo along microtubules towards the minus end, near the cell centre?
- AMyosin
- BActin
- CKinesin
- DDynein
4.Cell biologyHard
A non-competitive inhibitor binds an enzyme away from the active site. How does it change the kinetics?
- AIt has no effect at high substrate levels
- BVmax stays the same and Km rises
- CBoth Vmax and Km rise
- DVmax falls and Km stays the same
3Solutions
1.Genetics
Answer: Xb × Xb
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
XBY, XBXb, XbY, XbXb
Find the cell
Xb × Xb = XbXb
Answer
Cell Xb × Xb → XbXb
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: D · Dynein
Why this is the answer
Kinesins mostly move towards the plus end (out to the periphery) and dyneins towards the minus end (towards the centrosome). Myosin moves along actin.
Answer
D · Dynein
4.Cell biology
Answer: D · Vmax falls and Km stays the same
Why this is the answer
A pure non-competitive inhibitor reduces the number of working enzyme molecules, lowering Vmax. Substrate binding is unaffected, so Km stays the same.
Answer
D · Vmax falls and Km stays the same
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