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 affected father, XdY. The mother's gametes run down the side. Click the cell for a carrier daughter.
♀ XDXd♂ XdY
- 1Xd × Y
- 2Xd × Xd
- 3XD × Y
- 4XD × Xd
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives round seeds (dominant) or wrinkled seeds; gene B gives tall plants (dominant) or short plants. Click the one cell for an offspring that is shows both wrinkled seeds and short plants.
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
Gut epithelial cells take up glucose against its gradient with a sodium–glucose cotransporter. What kind of transport is this?
- ASimple diffusion
- BSecondary active transport
- CPrimary active transport
- DFacilitated diffusion
4.Cell biologyHard
Okazaki fragments are formed on:
- AThe leading strand
- BThe lagging strand during DNA replication
- CtRNA during transcription
- DmRNA during translation
3Solutions
1.Genetics
Answer: XD × Xd
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
XdY, XdXd, XDY, XDXd
Find the cell
XD × Xd = XDXd
Answer
Cell XD × Xd → XDXd
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 · Secondary active transport
Why this is the answer
The Na⁺/K⁺ pump uses ATP to make a sodium gradient. SGLT1 uses the energy of sodium flowing in to drag glucose in against its gradient.
Answer
B · Secondary active transport
4.Cell biology
Answer: B · The lagging strand during DNA replication
Why this is the answer
The lagging strand is synthesised discontinuously in short fragments away from the fork, then joined by ligase.
Answer
B · The lagging strand during DNA replication
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