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
A recessive condition affects 1 in 1600 of a population in Hardy–Weinberg equilibrium. What fraction f of the population are carriers (heterozygous)?
q² = 0.000625
f =
3.Cell biologyMedium
Active transport differs from facilitated diffusion because it:
- AMoves substances down their gradient faster by using carrier proteins
- BNeeds no proteins
- CUses energy to move substances against their concentration gradient
- DOnly moves water
4.Cell biologyHard
Which checkpoint ensures all chromosomes are attached to the spindle before anaphase begins?
- AThe S-phase checkpoint
- BThe spindle assembly (metaphase) checkpoint
- CThe G2/M checkpoint
- DThe G1/S checkpoint
3Solutions
1.Genetics
Answer: P = 0.5625
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) = 0.75
P(round seeds) = 0.75
Multiply
P = 0.75·0.75 = 0.5625
Answer
P = 0.5625
2.Genetics
Answer: f = 0.04875
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 = √0.000625 = 0.025
p = 1 − 0.025 = 0.975
Carriers
2pq = 2·0.975·0.025 = 0.04875
Answer
f = 0.04875
3.Cell biology
Answer: C · 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
C · Uses energy to move substances against their concentration gradient
4.Cell biology
Answer: B · 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
B · The spindle assembly (metaphase) checkpoint
ExamProblems · examproblems.com/courses/biology