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 × XD
- 2Xd × Y
- 3XD × XD
- 4XD × Y
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives purple flowers (dominant) or white flowers; gene B gives yellow seeds (dominant) or green seeds. Click the one cell for an offspring that is shows both white flowers and green 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
Which codon starts translation and which amino acid does it code for?
- AAUG, coding for glycine
- BUGA, coding for methionine
- CUAA, coding for leucine
- DAUG, coding for methionine
4.Cell biologyHard
Mitochondria have their own DNA, but where are most mitochondrial proteins made?
- AIn the Golgi apparatus
- BIn the rough ER and delivered by vesicles
- CInside the mitochondrion from mitochondrial genes
- DOn cytosolic ribosomes from nuclear genes, then imported
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
XdXD, XdY, XDXD, XDY
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 · AUG, coding for methionine
Why this is the answer
AUG is the usual start codon and codes for methionine. UAA, UAG and UGA are stop codons and code for no amino acid.
Answer
D · AUG, coding for methionine
4.Cell biology
Answer: D · On cytosolic ribosomes from nuclear genes, then imported
Why this is the answer
Most mitochondrial proteins are encoded in the nucleus, made in the cytosol and imported through the TOM and TIM translocases. Human mtDNA encodes only 13 proteins.
Answer
D · On cytosolic ribosomes from nuclear genes, then imported
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