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
red-green colour blindness is X-linked recessive (allele b). A carrier mother, XBXb, has children with an unaffected father, XBY. The mother's gametes run down the side. Click the cell for an unaffected son.
♀ XBXb♂ XBY
- 1XB × Y
- 2XB × XB
- 3Xb × Y
- 4Xb × XB
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives round seeds (dominant) or wrinkled seeds; gene B gives black fur (dominant) or white fur. Click the one cell for an offspring that is homozygous for round seeds and shows white fur.
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?
- AFacilitated diffusion
- BSecondary active transport
- CPrimary active transport
- DSimple diffusion
4.Cell biologyHard
How does a cell mark a damaged or short-lived protein for destruction by the proteasome?
- ABy removing all its phosphate groups
- BBy attaching a chain of ubiquitin molecules
- CBy adding mannose-6-phosphate
- DBy adding a signal sequence for the ER
3Solutions
1.Genetics
Answer: XB × 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
XBY, XBXB, XbY, XbXB
Find the cell
XB × Y = XBY
Answer
Cell XB × Y → XBY
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 · By attaching a chain of ubiquitin molecules
Why this is the answer
Enzymes attach a polyubiquitin chain to the target protein. The proteasome recognises this chain, unfolds the protein and breaks it into short peptides.
Answer
B · By attaching a chain of ubiquitin molecules
ExamProblems · examproblems.com/courses/biology