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 a carrier daughter.
♀ XBXb♂ XBY
- 1Xb × XB
- 2Xb × Y
- 3XB × XB
- 4XB × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives black fur (dominant) or white fur; gene B gives yellow seeds (dominant) or green seeds. Click the one cell for an offspring that is homozygous for black fur and for yellow seeds.
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 does it mean that the genetic code is "degenerate" (redundant)?
- AThe code differs completely between species
- BMost amino acids are coded by more than one codon
- CEach codon codes for several amino acids
- DSome codons are never used
4.Cell biologyHard
Bacteria moved to a much colder environment change the fatty acids in their membranes. Which change keeps the membrane fluid?
- AFewer membrane proteins
- BMore unsaturated fatty acids
- CLonger fatty acid tails
- DMore saturated fatty acids
3Solutions
1.Genetics
Answer: Xb × XB
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 × XB = XbXB
Answer
Cell Xb × XB → XbXB
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 · Most amino acids are coded by more than one codon
Why this is the answer
Several codons can code for the same amino acid, often differing in the third base. This is why many point mutations are silent.
Answer
B · Most amino acids are coded by more than one codon
4.Cell biology
Answer: B · More unsaturated fatty acids
Why this is the answer
Double bonds in unsaturated fatty acids create kinks that prevent tight packing, keeping the membrane fluid at low temperatures.
Answer
B · More unsaturated fatty acids
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