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
Tall (A) is dominant over short (a), and round seeds (B) over wrinkled (b). The genes are on different chromosomes. For the cross AaBb × aabb, what is the probability P that an offspring is tall, wrinkled seeds?
AaBb × aabb
P =
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 homozygous for black fur and shows short 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
Which tag added in the Golgi sends enzymes to the lysosomes?
- AUbiquitin
- BMannose-6-phosphate
- CA nuclear localisation signal
- DA KDEL sequence
4.Cell biologyHard
Which checkpoint ensures all chromosomes are attached to the spindle before anaphase begins?
- AThe G2/M checkpoint
- BThe G1/S checkpoint
- CThe spindle assembly (metaphase) checkpoint
- DThe S-phase checkpoint
3Solutions
1.Genetics
Answer: P = 0.25
Mendelian genetics: each parent passes on one allele of each gene, chosen at random. A Punnett square lists every combination of gametes, each equally likely. A dominant allele (capital letter) shows whenever it is present; a recessive one only in the homozygous form. Genes on different chromosomes are inherited independently, so their probabilities multiply.
Each gene on its own
P(tall) = 0.5
P(wrinkled seeds) = 0.5
Multiply
P = 0.5·0.5 = 0.25
Answer
P = 0.25
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 · Mannose-6-phosphate
Why this is the answer
In the Golgi, lysosomal enzymes receive mannose-6-phosphate. Receptors that bind this tag package them into vesicles bound for lysosomes.
Answer
B · Mannose-6-phosphate
4.Cell biology
Answer: C · The spindle assembly (metaphase) checkpoint
Why this is the answer
The spindle checkpoint delays anaphase until every kinetochore is attached, preventing unequal chromosome distribution.
Answer
C · The spindle assembly (metaphase) checkpoint
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