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
haemophilia is X-linked recessive (allele h). A carrier mother, XHXh, has children with an affected father, XhY. The mother's gametes run down the side. Click the cell for an affected son.
♀ XHXh♂ XhY
- 1Xh × Y
- 2Xh × Xh
- 3XH × Y
- 4XH × Xh
2.GeneticsHard
Two AaBb parents are crossed. Gene A gives round seeds (dominant) or wrinkled seeds; gene B gives black fur (dominant) or white fur. Click the one cell for an offspring that is shows both wrinkled seeds and white 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
How does glucose enter most body cells, such as red blood cells?
- ABy facilitated diffusion through GLUT carrier proteins
- BBy primary active transport using ATP directly at the membrane
- CBy simple diffusion through the lipid bilayer
- DBy phagocytosis
4.Cell biologyHard
A signal molecule that cannot cross the membrane, such as adrenaline, acts by:
- ABeing converted into ATP
- BBinding a surface receptor that triggers a second-messenger cascade
- CDiffusing into the nucleus and binding DNA to change gene transcription
- DDissolving the membrane
3Solutions
1.Genetics
Answer: Xh × 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
XhY, XhXh, XHY, XHXh
Find the cell
Xh × Y = XhY
Answer
Cell Xh × Y → XhY
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: A · By facilitated diffusion through GLUT carrier proteins
Why this is the answer
Glucose uses GLUT carrier proteins to move down its concentration gradient without using ATP. This is facilitated diffusion.
Answer
A · By facilitated diffusion through GLUT carrier proteins
4.Cell biology
Answer: B · Binding a surface receptor that triggers a second-messenger cascade
Why this is the answer
Hydrophilic signals bind membrane receptors (e.g. G-protein-coupled receptors), activating intracellular messengers; steroid hormones instead cross the membrane.
Answer
B · Binding a surface receptor that triggers a second-messenger cascade
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