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 an unaffected son.
♀ XDXd♂ XdY
- 1XD × Y
- 2XD × Xd
- 3Xd × Y
- 4Xd × Xd
2.GeneticsHard
A recessive condition affects 9% of a population in Hardy–Weinberg equilibrium. What fraction f of the population are carriers (heterozygous)?
q² = 0.09
f =
3.Cell biologyMedium
Which codon starts translation and which amino acid does it code for?
- AUGA, coding for methionine
- BAUG, coding for glycine
- CAUG, coding for methionine
- DUAA, coding for leucine
4.Cell biologyHard
Cyanide is rapidly lethal because it inhibits which component of the cell?
- ACytochrome c oxidase (complex IV)
- BATP synthase's rotor
- CThe Na⁺/K⁺ pump directly
- DHexokinase in glycolysis
3Solutions
1.Genetics
Answer: XD × 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
XDY, XDXd, XdY, XdXd
Find the cell
XD × Y = XDY
Answer
Cell XD × Y → XDY
2.Genetics
Answer: f = 0.42
Hardy–Weinberg: in a large, randomly mating population with no selection, the allele frequencies p (dominant) and q (recessive), p + q = 1, give genotype frequencies p², 2pq and q².
Allele frequencies
q = √0.09 = 0.3
p = 1 − 0.3 = 0.7
Carriers
2pq = 2·0.7·0.3 = 0.42
Answer
f = 0.42
3.Cell biology
Answer: C · AUG, coding for methionine
Why this is the answer
AUG is the usual start codon and codes for methionine. UAA, UAG and UGA are stop codons and code for no amino acid.
Answer
C · AUG, coding for methionine
4.Cell biology
Answer: A · Cytochrome c oxidase (complex IV)
Why this is the answer
Cyanide binds cytochrome c oxidase and stops electron transfer to oxygen. The proton gradient collapses and aerobic ATP production stops.
Answer
A · Cytochrome c oxidase (complex IV)
ExamProblems · examproblems.com/courses/biology