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.

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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 an affected son.

♀ 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 1% of a population in Hardy–Weinberg equilibrium. What fraction f of the population are carriers (heterozygous)?

q² = 0.01

f =

3.Cell biologyMedium

How does glucose enter most body cells, such as red blood cells?

ABy simple diffusion through the lipid bilayer
BBy facilitated diffusion through GLUT carrier proteins
CBy primary active transport using ATP directly at the membrane
DBy phagocytosis

4.Cell biologyHard

Sickle cell disease is caused by a single base substitution that changes glutamate to valine in beta-globin. What type of mutation is this?

AMissense mutation
BSilent mutation
CNonsense mutation
DFrameshift mutation

3Solutions

1.Genetics

Answer: X^h × Y

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 × Y = X^hY

Answer

Cell X^h × Y → X^hY

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: B · By facilitated diffusion through GLUT carrier proteins

Why this is the answer

Glucose uses GLUT carrier proteins to move down its concentration gradient without using ATP. This is facilitated diffusion.

Answer

B · By facilitated diffusion through GLUT carrier proteins

4.Cell biology

Answer: A · Missense mutation

Why this is the answer

A single base change (GAG to GTG) replaces one amino acid with another, a missense mutation. The hydrophobic valine makes deoxygenated haemoglobin polymerise.

Answer

A · Missense mutation

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