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

haemophilia is X-linked recessive (allele h). A carrier mother, X^HX^h, has children with an unaffected father, X^HY. The mother's gametes run down the side. Click the cell for a carrier daughter.

♀ X^HX^h♂ X^HY

1X^h × X^H
2X^h × Y
3X^H × X^H
4X^H × Y

2.GeneticsHard

A recessive condition affects 16% of a population in Hardy–Weinberg equilibrium. What fraction f of the population are carriers (heterozygous)?

q² = 0.16

f =

3.Cell biologyMedium

Which enzyme makes the second messenger cyclic AMP when activated by a Gs protein?

APhosphodiesterase
BAdenylyl cyclase
CPhospholipase C
DProtein kinase A

4.Cell biologyHard

Bacteria moved to a much colder environment change the fatty acids in their membranes. Which change keeps the membrane fluid?

AMore unsaturated fatty acids
BLonger fatty acid tails
CMore saturated fatty acids
DFewer membrane proteins

3Solutions

1.Genetics

Answer: X^h × X^H

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^hX^H, X^hY, X^HX^H, X^HY

Find the cell

X^h × X^H = X^hX^H

Answer

Cell X^h × X^H → X^hX^H

2.Genetics

Answer: f = 0.48

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 = √0.16 = 0.4

p = 1 − 0.4 = 0.6

Carriers

2pq = 2·0.6·0.4 = 0.48

Answer

f = 0.48

3.Cell biology

Answer: B · Adenylyl cyclase

Why this is the answer

Activated Gs stimulates adenylyl cyclase to convert ATP into cAMP. cAMP activates protein kinase A, and phosphodiesterase breaks cAMP down.

Answer

B · Adenylyl cyclase

4.Cell biology

Answer: A · More unsaturated fatty acids

Why this is the answer

Double bonds in unsaturated fatty acids create kinks that prevent tight packing, keeping the membrane fluid at low temperatures.

Answer

A · More unsaturated fatty acids

ExamProblems · examproblems.com/courses/biology