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
red-green colour blindness is X-linked recessive (allele b). A carrier mother, XBXb, has children with an unaffected father, XBY. The mother's gametes run down the side. Click the cell for a carrier daughter.
♀ XBXb♂ XBY
- 1Xb × Y
- 2Xb × XB
- 3XB × Y
- 4XB × XB
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 shows both wrinkled seeds and short 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
What is the G0 phase of the cell cycle?
- AThe phase in which DNA is copied
- BThe final stage of mitosis
- CA phase found only in cancer cells that have stopped responding to signals
- DA resting state in which cells have left the cycle and stopped dividing
4.Cell biologyHard
In Griffith's 1928 experiment, mice injected with heat-killed smooth (S) pneumococci plus live rough (R) bacteria died. What did this show?
- AA substance from the dead S cells transformed R cells into a virulent form
- BR bacteria are virulent on their own
- CMice make S bacteria from R bacteria
- DHeat does not kill S bacteria
3Solutions
1.Genetics
Answer: Xb × XB
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
XbY, XbXB, XBY, XBXB
Find the cell
Xb × XB = XbXB
Answer
Cell Xb × XB → XbXB
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 · A resting state in which cells have left the cycle and stopped dividing
Why this is the answer
Cells in G0 have exited the cycle and do not prepare to divide. Some can return to G1 when stimulated, such as liver cells after injury.
Answer
D · A resting state in which cells have left the cycle and stopped dividing
4.Cell biology
Answer: A · A substance from the dead S cells transformed R cells into a virulent form
Why this is the answer
Something from the heat-killed S strain changed living R bacteria into the virulent S type. Griffith called this transformation; the "transforming principle" was later shown to be DNA.
Answer
A · A substance from the dead S cells transformed R cells into a virulent form
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