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
Duchenne muscular dystrophy is X-linked recessive (allele d). A carrier mother, XDXd, has children with an unaffected father, XDY. The mother's gametes run down the side. Click the cell for an unaffected son.
♀ XDXd♂ XDY
- 1XD × Y
- 2XD × XD
- 3Xd × Y
- 4Xd × XD
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 homozygous for tall plants and 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
What is crossing over during meiosis?
- AFusion of two gametes
- BSeparation of sister chromatids as they move to opposite poles in anaphase II
- CCopying of DNA before division
- DExchange of genetic material between homologous chromosomes in prophase I
4.Cell biologyHard
In Michaelis–Menten kinetics, what does the Km of an enzyme represent?
- AThe amount of enzyme in the cell
- BThe substrate concentration at which the rate is half of Vmax
- CThe maximum rate of the reaction
- DThe reaction rate when the substrate concentration is close to zero
3Solutions
1.Genetics
Answer: XD × 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
XDY, XDXD, XdY, XdXD
Find the cell
XD × Y = XDY
Answer
Cell XD × Y → XDY
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 · Exchange of genetic material between homologous chromosomes in prophase I
Why this is the answer
Non-sister chromatids of homologous chromosomes exchange segments at chiasmata, increasing genetic variation.
Answer
D · Exchange of genetic material between homologous chromosomes in prophase I
4.Cell biology
Answer: B · The substrate concentration at which the rate is half of Vmax
Why this is the answer
Km is the substrate concentration giving half the maximum velocity. A low Km indicates high apparent affinity for the substrate.
Answer
B · The substrate concentration at which the rate is half of Vmax
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