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 a carrier daughter.
♀ XHXh♂ XhY
- 1XH × Y
- 2XH × Xh
- 3Xh × Y
- 4Xh × Xh
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives black fur (dominant) or white fur; gene B gives round seeds (dominant) or wrinkled seeds. Click the one cell for an offspring that is homozygous for black fur and shows wrinkled 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 role does cholesterol play in animal cell membranes?
- AIt forms channels for ions
- BIt helps keep membrane fluidity stable across temperatures
- CIt makes the membrane completely rigid at every temperature
- DIt is the main carrier of glucose
4.Cell biologyHard
A signal molecule that cannot cross the membrane, such as adrenaline, acts by:
- ADiffusing into the nucleus and binding DNA to change gene transcription
- BBinding a surface receptor that triggers a second-messenger cascade
- CBeing converted into ATP
- DDissolving the membrane
3Solutions
1.Genetics
Answer: XH × Xh
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 × Xh = XHXh
Answer
Cell XH × Xh → XHXh
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 · It helps keep membrane fluidity stable across temperatures
Why this is the answer
Cholesterol reduces fluidity at high temperatures and prevents tight packing at low temperatures, buffering membrane fluidity.
Answer
B · It helps keep membrane fluidity stable across temperatures
4.Cell biology
Answer: B · Binding a surface receptor that triggers a second-messenger cascade
Why this is the answer
Hydrophilic signals bind membrane receptors (e.g. G-protein-coupled receptors), activating intracellular messengers; steroid hormones instead cross the membrane.
Answer
B · Binding a surface receptor that triggers a second-messenger cascade
ExamProblems · examproblems.com/courses/biology