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, wrinkled seeds?
AaBb × AaBb
P =
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives black fur (dominant) or white fur; gene B gives tall plants (dominant) or short plants. Click the one cell for an offspring that is shows both white fur 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
Cyclin-dependent kinases (CDKs) that drive the cell cycle become active when they bind to:
- ATubulins
- BHistones
- CCyclins
- DRibosomes
4.Cell biologyHard
A non-competitive inhibitor binds an enzyme away from the active site. How does it change the kinetics?
- AVmax falls and Km stays the same
- BIt has no effect at high substrate levels
- CVmax stays the same and Km rises
- DBoth Vmax and Km rise
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(tall) = 0.75
P(wrinkled seeds) = 0.25
Multiply
P = 0.75·0.25 = 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: C · Cyclins
Why this is the answer
CDKs are only active when bound to cyclins, whose levels rise and fall through the cycle. Active cyclin–CDK complexes phosphorylate targets that push the cell forward.
Answer
C · Cyclins
4.Cell biology
Answer: A · Vmax falls and Km stays the same
Why this is the answer
A pure non-competitive inhibitor reduces the number of working enzyme molecules, lowering Vmax. Substrate binding is unaffected, so Km stays the same.
Answer
A · Vmax falls and Km stays the same
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