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, round seeds?
AaBb × aabb
P =
2.GeneticsHard
In a population of 2000 in Hardy–Weinberg equilibrium, 9% show a recessive trait. How many individuals N are expected to be homozygous dominant?
N = 2000q² = 0.09
N =
3.Cell biologyMedium
Active transport differs from facilitated diffusion because it:
- ANeeds no proteins
- BOnly moves water
- CMoves substances down their gradient faster by using carrier proteins
- DUses energy to move substances against their concentration gradient
4.Cell biologyHard
Which checkpoint ensures all chromosomes are attached to the spindle before anaphase begins?
- AThe G1/S checkpoint
- BThe S-phase checkpoint
- CThe G2/M checkpoint
- DThe spindle assembly (metaphase) 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(round seeds) = 0.5
Multiply
P = 0.5·0.5 = 0.25
Answer
P = 0.25
2.Genetics
Answer: N = 980
Hardy–Weinberg: in a large, randomly mating population with no selection, the allele frequencies p (dominant) and q (recessive), p + q = 1, give genotype frequencies p², 2pq and q².
Allele frequencies
q = √0.09 = 0.3
p = 0.7
Homozygous dominant
p² = 0.49
N = 2000·0.49 = 980
Answer
N = 980
3.Cell biology
Answer: D · Uses energy to move substances against their concentration gradient
Why this is the answer
Active transport uses ATP (or another gradient) to move molecules against their gradient; facilitated diffusion is passive.
Answer
D · Uses energy to move substances against their concentration gradient
4.Cell biology
Answer: D · 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
D · The spindle assembly (metaphase) checkpoint
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