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 a carrier daughter.

♀ X^HX^h♂ X^HY

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

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

Where in the cell does the citric acid (Krebs) cycle take place?

AMitochondrial matrix
BInner mitochondrial membrane
CIntermembrane space
DCytoplasm

4.Cell biologyHard

The endosymbiotic theory is supported by the fact that mitochondria:

AHave their own circular DNA and 70S-like ribosomes
BAre made in the nucleus
CContain chlorophyll
DHave no membranes

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

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: A · 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

A · Mitochondrial matrix

4.Cell biology

Answer: A · Have their own circular DNA and 70S-like ribosomes

Why this is the answer

Mitochondria and chloroplasts have circular DNA, bacterial-like ribosomes, double membranes and divide by fission, suggesting a bacterial origin.

Answer

A · Have their own circular DNA and 70S-like ribosomes

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