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 an unaffected son.
♀ XHXh♂ XhY
- 1Xh × Y
- 2Xh × Xh
- 3XH × Y
- 4XH × Xh
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 green seeds and is homozygous for purple 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
Which tag added in the Golgi sends enzymes to the lysosomes?
- AA KDEL sequence
- BUbiquitin
- CA nuclear localisation signal
- DMannose-6-phosphate
4.Cell biologyHard
In the most common cystic fibrosis mutation (ΔF508), the CFTR protein is made but is missing from the cell membrane. Why?
- AThe mRNA cannot leave the nucleus
- BThe gene is not transcribed at all
- CThe misfolded protein is held in the ER and degraded
- DThe protein is secreted out of the cell instead of being inserted
3Solutions
1.Genetics
Answer: XH × 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
XhY, XhXh, XHY, XHXh
Find the cell
XH × Y = XHY
Answer
Cell XH × Y → XHY
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: D · Mannose-6-phosphate
Why this is the answer
In the Golgi, lysosomal enzymes receive mannose-6-phosphate. Receptors that bind this tag package them into vesicles bound for lysosomes.
Answer
D · Mannose-6-phosphate
4.Cell biology
Answer: C · The misfolded protein is held in the ER and degraded
Why this is the answer
Loss of one phenylalanine makes CFTR misfold. ER quality control retains it and sends it for proteasomal degradation, so little reaches the membrane.
Answer
C · The misfolded protein is held in the ER and degraded
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