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 short, round seeds?
AaBb × Aabb
P =
2.GeneticsHard
In a population of 500 in Hardy–Weinberg equilibrium, 1 in 2500 show a recessive trait. How many individuals N are expected to be homozygous dominant?
N = 500q² = 0.0004
N =
3.Cell biologyMedium
Where in the cell does the citric acid (Krebs) cycle take place?
- AInner mitochondrial membrane
- BCytoplasm
- CIntermembrane space
- DMitochondrial matrix
4.Cell biologyHard
A double-stranded DNA sample contains 30% adenine. What percentage is guanine?
- A40%
- B70%
- C20%
- D30%
3Solutions
1.Genetics
Answer: P = 0.125
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(short) = 0.25
P(round seeds) = 0.5
Multiply
P = 0.25·0.5 = 0.125
Answer
P = 0.125
2.Genetics
Answer: N = 480.2
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 = √0.0004 = 0.02
p = 0.98
Homozygous dominant
p² = 0.9604
N = 500·0.9604 = 480.2
Answer
N = 480.2
3.Cell biology
Answer: D · Mitochondrial matrix
Why this is the answer
The citric acid cycle runs in the mitochondrial matrix, producing NADH, FADH₂ and CO₂. The electron transport chain sits in the inner membrane.
Answer
D · Mitochondrial matrix
4.Cell biology
Answer: C · 20%
Why this is the answer
A = T = 30%, so A + T = 60%. The remaining 40% is split equally between G and C, so G = 20%.
Answer
C · 20%
ExamProblems · examproblems.com/courses/biology