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 × XH
- 2XH × Y
- 3Xh × XH
- 4Xh × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives round seeds (dominant) or wrinkled seeds; gene B gives purple flowers (dominant) or white flowers. Click the one cell for an offspring that is shows wrinkled seeds and is homozygous 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
Which enzyme makes the second messenger cyclic AMP when activated by a Gs protein?
- APhosphodiesterase
- BAdenylyl cyclase
- CPhospholipase C
- DProtein kinase A
4.Cell biologyHard
The endosymbiotic theory is supported by the fact that mitochondria:
- AContain chlorophyll
- BHave their own circular DNA and 70S-like ribosomes
- CHave no membranes
- DAre made in the nucleus
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
XHXH, XHY, XhXH, XhY
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: B · Adenylyl cyclase
Why this is the answer
Activated Gs stimulates adenylyl cyclase to convert ATP into cAMP. cAMP activates protein kinase A, and phosphodiesterase breaks cAMP down.
Answer
B · Adenylyl cyclase
4.Cell biology
Answer: B · Have their own circular DNA and 70S-like ribosomes
Why this is the answer
Mitochondria and chloroplasts have circular DNA, bacterial-like ribosomes, double membranes and divide by fission, suggesting a bacterial origin.
Answer
B · Have their own circular DNA and 70S-like ribosomes
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