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
haemophilia is X-linked recessive (allele h). A carrier mother, XHXh, has children with an affected father, XhY. The mother's gametes run down the side. Click the cell for an affected son.
♀ XHXh♂ XhY
- 1XH × Y
- 2XH × Xh
- 3Xh × Y
- 4Xh × Xh
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
A competitive inhibitor binds the active site of an enzyme. What can overcome its effect?
- ALowering the temperature to 0 °C
- BRemoving the enzyme's cofactor
- CRaising the inhibitor concentration
- DRaising the substrate concentration
4.Cell biologyHard
Mitochondria have their own DNA, but where are most mitochondrial proteins made?
- AOn cytosolic ribosomes from nuclear genes, then imported
- BInside the mitochondrion from mitochondrial genes
- CIn the rough ER and delivered by vesicles
- DIn the Golgi apparatus
3Solutions
1.Genetics
Answer: Xh × 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
XHY, XHXh, XhY, XhXh
Find the cell
Xh × Y = XhY
Answer
Cell Xh × Y → XhY
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 · Raising the substrate concentration
Why this is the answer
Because substrate and inhibitor compete for the active site, enough substrate can outcompete the inhibitor. Vmax is unchanged but the apparent Km rises.
Answer
D · Raising the substrate concentration
4.Cell biology
Answer: A · On cytosolic ribosomes from nuclear genes, then imported
Why this is the answer
Most mitochondrial proteins are encoded in the nucleus, made in the cytosol and imported through the TOM and TIM translocases. Human mtDNA encodes only 13 proteins.
Answer
A · On cytosolic ribosomes from nuclear genes, then imported
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