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 short, round seeds?
AaBb × AaBb
P =
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 shows green 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
A competitive inhibitor binds the active site of an enzyme. What can overcome its effect?
- ARaising the substrate concentration
- BLowering the temperature to 0 °C
- CRemoving the enzyme's cofactor
- DRaising the inhibitor concentration
4.Cell biologyHard
Some antibiotics, such as tetracyclines, block bacterial protein synthesis with little effect on human cytoplasmic ribosomes. Why?
- ABacteria use DNA instead of mRNA as the template for translation on ribosomes
- BHuman ribosomes are inside the nucleus
- CHuman cells do not make proteins
- DBacterial 70S ribosomes differ in structure from eukaryotic 80S ribosomes
3Solutions
1.Genetics
Answer: P = 0.1875
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(short) = 0.25
P(round seeds) = 0.75
Multiply
P = 0.25·0.75 = 0.1875
Answer
P = 0.1875
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 · 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
A · Raising the substrate concentration
4.Cell biology
Answer: D · Bacterial 70S ribosomes differ in structure from eukaryotic 80S ribosomes
Why this is the answer
Bacterial ribosomes (70S: 30S + 50S) differ from cytoplasmic eukaryotic ribosomes (80S: 40S + 60S), so drugs can target them selectively.
Answer
D · Bacterial 70S ribosomes differ in structure from eukaryotic 80S ribosomes
ExamProblems · examproblems.com/courses/biology