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% of a population in Hardy–Weinberg equilibrium. What fraction f of the population are carriers (heterozygous)?
q² = 0.01
f =
3.Cell biologyMedium
Gut epithelial cells take up glucose against its gradient with a sodium–glucose cotransporter. What kind of transport is this?
- ASecondary active transport
- BFacilitated diffusion
- CPrimary active transport
- DSimple diffusion
4.Cell biologyHard
In damaged tissue, cells swell, their membranes burst and the area becomes inflamed. Which type of cell death is this?
- ASenescence
- BNecrosis
- CApoptosis
- DMitosis
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 = 0.18
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 = √0.01 = 0.1
p = 1 − 0.1 = 0.9
Carriers
2pq = 2·0.9·0.1 = 0.18
Answer
f = 0.18
3.Cell biology
Answer: A · Secondary active transport
Why this is the answer
The Na⁺/K⁺ pump uses ATP to make a sodium gradient. SGLT1 uses the energy of sodium flowing in to drag glucose in against its gradient.
Answer
A · Secondary active transport
4.Cell biology
Answer: B · Necrosis
Why this is the answer
Necrosis is uncontrolled death with swelling, membrane rupture and leakage of contents that trigger inflammation. Apoptosis is orderly shrinkage into apoptotic bodies that are removed quietly.
Answer
B · Necrosis
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