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 unaffected father, XBY. The mother's gametes run down the side. Click the cell for an affected son.
♀ XBXb♂ XBY
- 1XB × XB
- 2XB × Y
- 3Xb × XB
- 4Xb × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives tall plants (dominant) or short plants; gene B gives yellow seeds (dominant) or green seeds. Click the one cell for an offspring that is shows short plants and is homozygous for yellow 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
What directly drives ATP synthase to make ATP in mitochondria?
- AElectrons from NADH flowing directly through ATP synthase
- BProtons flowing back into the matrix down their gradient
- CGlucose binding to ATP synthase
- DOxygen diffusing into the matrix
4.Cell biologyHard
A disease is passed from an affected mother to all her children but never from an affected father. Where is the mutation most likely located?
- AOn the X chromosome, as a dominant trait
- BIn mitochondrial DNA
- COn an autosome, as a recessive trait
- DOn the Y chromosome
3Solutions
1.Genetics
Answer: Xb × 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
XBXB, XBY, XbXB, XbY
Find the cell
Xb × Y = XbY
Answer
Cell Xb × Y → XbY
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 · Protons flowing back into the matrix down their gradient
Why this is the answer
The electron transport chain pumps protons into the intermembrane space. Their flow back through ATP synthase turns it and powers ATP synthesis.
Answer
B · Protons flowing back into the matrix down their gradient
4.Cell biology
Answer: B · In mitochondrial DNA
Why this is the answer
Mitochondria, and their DNA, are inherited almost only from the egg. Mitochondrial disorders therefore follow maternal inheritance.
Answer
B · In mitochondrial DNA
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