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
Tall (A) is dominant over short (a), and round seeds (B) over wrinkled (b). The genes are on different chromosomes. For the cross AaBb × Aabb, what is the probability P that an offspring is tall, round seeds?
AaBb × Aabb
P =
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives purple flowers (dominant) or white flowers; gene B gives tall plants (dominant) or short plants. Click the one cell for an offspring that is shows white flowers and is homozygous for tall 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
A competitive inhibitor binds the active site of an enzyme. What can overcome its effect?
- ARaising the inhibitor concentration
- BRaising the substrate concentration
- CLowering the temperature to 0 °C
- DRemoving the enzyme's cofactor
4.Cell biologyHard
Where in the cell does the electron transport chain of aerobic respiration take place?
- AOuter mitochondrial membrane
- BMitochondrial matrix
- CInner mitochondrial membrane
- DCytoplasm
3Solutions
1.Genetics
Answer: P = 0.375
Mendelian genetics: each parent passes on one allele of each gene, chosen at random. A Punnett square lists every combination of gametes, each equally likely. A dominant allele (capital letter) shows whenever it is present; a recessive one only in the homozygous form. Genes on different chromosomes are inherited independently, so their probabilities multiply.
Each gene on its own
P(tall) = 0.75
P(round seeds) = 0.5
Multiply
P = 0.75·0.5 = 0.375
Answer
P = 0.375
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 · Raising the substrate concentration
Why this is the answer
Because substrate and inhibitor compete for the active site, enough substrate can outcompete the inhibitor. Vmax is unchanged but the apparent Km rises.
Answer
B · Raising the substrate concentration
4.Cell biology
Answer: C · Inner mitochondrial membrane
Why this is the answer
Complexes of the ETC sit in the inner membrane, pumping protons into the intermembrane space; ATP synthase uses the gradient.
Answer
C · Inner mitochondrial membrane
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