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 a carrier 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 homozygous for purple flowers and for black 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
How do large proteins such as transcription factors enter the nucleus?
- ABy diffusing freely through the nuclear membrane lipids
- BThey are made inside the nucleus by nuclear ribosomes, so they never enter
- CBy exocytosis from the endoplasmic reticulum
- DThrough nuclear pore complexes, guided by a nuclear localisation signal
4.Cell biologyHard
Brown fat contains thermogenin (UCP1), which lets protons leak back across the inner mitochondrial membrane. What is the effect?
- AMore ATP is made per glucose
- BThe cell switches to fermentation
- CThe electron transport chain stops working because protons can no longer be pumped
- DEnergy from the proton gradient is released as heat instead of making ATP
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 · Through nuclear pore complexes, guided by a nuclear localisation signal
Why this is the answer
Proteins with a nuclear localisation signal are recognised by importins and carried through nuclear pore complexes. Translation happens in the cytoplasm.
Answer
D · Through nuclear pore complexes, guided by a nuclear localisation signal
4.Cell biology
Answer: D · Energy from the proton gradient is released as heat instead of making ATP
Why this is the answer
Uncoupling proteins let protons return to the matrix without passing ATP synthase. Electron transport continues, but the energy is released as heat, which is useful in newborns.
Answer
D · Energy from the proton gradient is released as heat instead of making ATP
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