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 unaffected 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 yellow seeds (dominant) or green seeds; gene B gives purple flowers (dominant) or white flowers. Click the one cell for an offspring that is shows both green seeds and white flowers.
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 separates during anaphase I of meiosis?
- ASister chromatids
- BHomologous chromosomes
- CWhole nuclei
- DCentromeres of each chromatid
4.Cell biologyHard
Which statement about the sodium–potassium pump is correct?
- AIt moves 2 Na⁺ out and 3 K⁺ in
- BIt moves 3 Na⁺ out and 2 K⁺ in for each ATP used
- CIt needs no energy
- DIt moves Na⁺ and K⁺ in the same direction across the membrane
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 · Homologous chromosomes
Why this is the answer
In anaphase I, homologous chromosomes move to opposite poles, halving the chromosome number. Sister chromatids separate in anaphase II.
Answer
B · Homologous chromosomes
4.Cell biology
Answer: B · It moves 3 Na⁺ out and 2 K⁺ in for each ATP used
Why this is the answer
The Na⁺/K⁺-ATPase exports 3 Na⁺ and imports 2 K⁺ per ATP, maintaining gradients and contributing to the resting potential.
Answer
B · It moves 3 Na⁺ out and 2 K⁺ in for each ATP used
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