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 unaffected 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 round seeds (dominant) or wrinkled seeds; gene B gives tall plants (dominant) or short plants. Click the one cell for an offspring that is homozygous for round seeds and for tall plants.
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
A newly made protein has an N-terminal signal sequence. Where is it directed?
- AInto the endoplasmic reticulum
- BInto the nucleus
- CInto the mitochondrial matrix
- DDirectly to the cytosol for use there
4.Cell biologyHard
A mutation in the lac repressor stops it binding to the operator. What is the result?
- AThe lac genes are expressed all the time, even without lactose
- BThe lac genes are expressed only when glucose is present in the medium
- CThe lac genes can never be expressed
- DThe bacteria can no longer take up glucose
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: A · Into the endoplasmic reticulum
Why this is the answer
The signal recognition particle (SRP) binds the signal sequence and brings the ribosome to the ER membrane, where the protein enters the ER lumen or membrane.
Answer
A · Into the endoplasmic reticulum
4.Cell biology
Answer: A · The lac genes are expressed all the time, even without lactose
Why this is the answer
If the repressor cannot bind the operator, RNA polymerase is never blocked, so the operon is constitutively expressed.
Answer
A · The lac genes are expressed all the time, even without lactose
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