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 an affected son.
♀ XBXb♂ XBY
- 1XB × Y
- 2XB × XB
- 3Xb × Y
- 4Xb × XB
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 white fur and is homozygous for tall 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
A newly made protein has an N-terminal signal sequence. Where is it directed?
- AInto the nucleus
- BDirectly to the cytosol for use there
- CInto the mitochondrial matrix
- DInto the endoplasmic reticulum
4.Cell biologyHard
Why can translation in bacteria begin before transcription of the mRNA is finished?
- ABacterial ribosomes can read the DNA template directly in the cytoplasm
- BThere is no nuclear envelope separating DNA from ribosomes
- CBacteria do not use mRNA
- DBacterial mRNA is spliced faster
3Solutions
1.Genetics
Answer: Xb × 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
XBY, XBXB, XbY, XbXB
Find the cell
Xb × Y = XbY
Answer
Cell Xb × Y → XbY
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 · Into the endoplasmic reticulum
Why this is the answer
The signal recognition particle (SRP) binds the signal sequence and brings the ribosome to the ER membrane, where the protein enters the ER lumen or membrane.
Answer
D · Into the endoplasmic reticulum
4.Cell biology
Answer: B · There is no nuclear envelope separating DNA from ribosomes
Why this is the answer
In prokaryotes DNA lies in the cytoplasm, so ribosomes can attach to mRNA while it is still being made. In eukaryotes mRNA must be processed and exported first.
Answer
B · There is no nuclear envelope separating DNA from ribosomes
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