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 an unaffected son.
♀ XBXb♂ XBY
- 1Xb × XB
- 2Xb × Y
- 3XB × XB
- 4XB × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives tall plants (dominant) or short plants; gene B gives black fur (dominant) or white fur. Click the one cell for an offspring that is shows short plants and is homozygous for black fur.
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?
- APhospholipase C
- BPhosphodiesterase
- CProtein kinase A
- DAdenylyl cyclase
4.Cell biologyHard
With 23 chromosome pairs, how many different chromosome combinations can independent assortment alone produce in human gametes?
- A2 × 23
- B46
- C23²
- D2²³ (about 8 million)
3Solutions
1.Genetics
Answer: XB × 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
XbXB, XbY, XBXB, XBY
Find the cell
XB × Y = XBY
Answer
Cell XB × Y → XBY
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 · 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
D · Adenylyl cyclase
4.Cell biology
Answer: D · 2²³ (about 8 million)
Why this is the answer
Each of the 23 pairs can orient two ways, giving 2²³ ≈ 8.4 million combinations, even before crossing over adds more variation.
Answer
D · 2²³ (about 8 million)
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