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 yellow seeds (dominant) or green seeds; gene B gives purple flowers (dominant) or white flowers. Click the one cell for an offspring that is homozygous for yellow seeds and 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
Why does DNA replication need primase?
- ADNA polymerase can only extend an existing strand, so a short RNA primer is needed
- BPrimase unwinds the DNA double helix
- CPrimase proofreads the new DNA
- DPrimase joins the Okazaki fragments together once their RNA primers have been removed
4.Cell biologyHard
What problem does telomerase solve?
- AThe joining of Okazaki fragments
- BThe shortening of chromosome ends with each round of replication
- CThe unwinding of the double helix at each replication fork by helicase
- DThe removal of introns from mRNA
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: A · DNA polymerase can only extend an existing strand, so a short RNA primer is needed
Why this is the answer
Primase makes a short RNA primer with a free 3′ end. DNA polymerase extends it; the primer is later removed and replaced with DNA.
Answer
A · DNA polymerase can only extend an existing strand, so a short RNA primer is needed
4.Cell biology
Answer: B · 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
B · The shortening of chromosome ends with each round of replication
ExamProblems · examproblems.com/courses/biology