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 a carrier daughter.
♀ XHXh♂ XHY
- 1Xh × XH
- 2Xh × Y
- 3XH × XH
- 4XH × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives tall plants (dominant) or short plants; gene B gives round seeds (dominant) or wrinkled seeds. Click the one cell for an offspring that is homozygous for tall plants and for round 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 Golgi apparatus mainly:
- AReplicates DNA
- BBreaks down old organelles and engulfed bacteria with enzymes
- CModifies, sorts and packages proteins for transport
- DProduces ATP
4.Cell biologyHard
What problem does telomerase solve?
- AThe removal of introns from mRNA
- BThe unwinding of the double helix at each replication fork by helicase
- CThe joining of Okazaki fragments
- DThe shortening of chromosome ends with each round of replication
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
XhXH, XhY, XHXH, XHY
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: C · Modifies, sorts and packages proteins for transport
Why this is the answer
The Golgi modifies proteins (e.g. glycosylation) and sorts them into vesicles for secretion, membranes or lysosomes.
Answer
C · Modifies, sorts and packages proteins for transport
4.Cell biology
Answer: D · The shortening of chromosome ends with each round of replication
Why this is the answer
Telomerase uses its own RNA template to add repeats to telomeres, balancing the end-replication problem. It is active in stem cells and most cancer cells.
Answer
D · The shortening of chromosome ends with each round of replication
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