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.

In the print window, choose “Save as PDF” to keep a copy on your device.

1Formulas and methods

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

2Practice problems

1.GeneticsMedium

Duchenne muscular dystrophy is X-linked recessive (allele d). A carrier mother, X^DX^d, has children with an affected father, X^dY. The mother's gametes run down the side. Click the cell for a carrier daughter.

♀ X^DX^d♂ X^dY

1X^d × X^d
2X^d × Y
3X^D × X^d
4X^D × Y

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

The contractile ring that pinches an animal cell in two during cytokinesis is made of:

AKeratin filaments
BCellulose fibres
CMicrotubules and kinesin
DActin and myosin

4.Cell biologyHard

Some antibiotics, such as tetracyclines, block bacterial protein synthesis with little effect on human cytoplasmic ribosomes. Why?

AHuman ribosomes are inside the nucleus
BHuman cells do not make proteins
CBacterial 70S ribosomes differ in structure from eukaryotic 80S ribosomes
DBacteria use DNA instead of mRNA as the template for translation on ribosomes

3Solutions

1.Genetics

Answer: X^D × X^d

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.

Fill the square

X^dX^d, X^dY, X^DX^d, X^DY

Find the cell

X^D × X^d = X^DX^d

Answer

Cell X^D × X^d → X^DX^d

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: D · Actin and myosin

Why this is the answer

A ring of actin filaments and myosin II contracts under the membrane, forming the cleavage furrow that separates the two daughter cells.

Answer

D · Actin and myosin

4.Cell biology

Answer: C · Bacterial 70S ribosomes differ in structure from eukaryotic 80S ribosomes

Why this is the answer

Bacterial ribosomes (70S: 30S + 50S) differ from cytoplasmic eukaryotic ribosomes (80S: 40S + 60S), so drugs can target them selectively.

Answer

C · Bacterial 70S ribosomes differ in structure from eukaryotic 80S ribosomes

ExamProblems · examproblems.com/courses/biology