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 an affected son.
♀ XDXd♂ XDY
- 1Xd × Y
- 2Xd × XD
- 3XD × Y
- 4XD × XD
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives round seeds (dominant) or wrinkled seeds; gene B gives yellow seeds (dominant) or green seeds. Click the one cell for an offspring that is homozygous for round seeds and for yellow 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
The contractile ring that pinches an animal cell in two during cytokinesis is made of:
- AMicrotubules and kinesin
- BKeratin filaments
- CActin and myosin
- DCellulose fibres
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 misfolded protein is held in the ER and degraded
- CThe gene is not transcribed at all
- DThe protein is secreted out of the cell instead of being inserted
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: 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: C · Actin and myosin
Why this is the answer
A ring of actin filaments and myosin II contracts under the membrane, forming the cleavage furrow that separates the two daughter cells.
Answer
C · Actin and myosin
4.Cell biology
Answer: B · 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
B · The misfolded protein is held in the ER and degraded
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