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 yellow seeds (dominant) or green seeds; gene B gives tall plants (dominant) or short plants. Click the one cell for an offspring that is homozygous for yellow seeds and 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
During which phase of mitosis do sister chromatids separate?
- AMetaphase
- BAnaphase
- CProphase
- DTelophase
4.Cell biologyHard
How can one human gene produce several different proteins?
- ABy alternative splicing of its pre-mRNA
- BBy copying the gene into different chromosomes
- CBy reading the gene in all three frames at once
- DBy using a different genetic code in each tissue
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: B · Anaphase
Why this is the answer
In anaphase cohesin is cleaved and chromatids are pulled to opposite poles by spindle microtubules.
Answer
B · Anaphase
4.Cell biology
Answer: A · By alternative splicing of its pre-mRNA
Why this is the answer
Alternative splicing joins different combinations of exons from the same pre-mRNA, producing related proteins from one gene.
Answer
A · By alternative splicing of its pre-mRNA
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