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
♂♀Xh​YXh​XH​

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

♀ XHXh♂ XhY
  1. 1Xh × Xh
  2. 2Xh × Y
  3. 3XH × Xh
  4. 4XH × Y
2.GeneticsHard
♂ AaBb♀ AaBbABabaBAbaBabABAb

Two AaBb parents are crossed. Gene A gives purple flowers (dominant) or white flowers; gene B gives yellow seeds (dominant) or green seeds. Click the one cell for an offspring that is homozygous for purple flowers and shows green seeds.

AaBb × AaBb
  1. 1aB × AB
  2. 2aB × ab
  3. 3aB × aB
  4. 4aB × Ab
  5. 5ab × AB
  6. 6ab × ab
  7. 7ab × aB
  8. 8ab × Ab
  9. 9AB × AB
  10. 10AB × ab
  11. 11AB × aB
  12. 12AB × Ab
  13. 13Ab × AB
  14. 14Ab × ab
  15. 15Ab × aB
  16. 16Ab × Ab
3.Cell biologyMedium

What is the net ATP yield of glycolysis per molecule of glucose?

  1. A36 ATP
  2. B2 ATP
  3. C4 ATP
  4. D1 ATP
4.Cell biologyHard

A disease is passed from an affected mother to all her children but never from an affected father. Where is the mutation most likely located?

  1. AOn the Y chromosome
  2. BOn an autosome, as a recessive trait
  3. CIn mitochondrial DNA
  4. DOn the X chromosome, as a dominant trait

3Solutions

1.Genetics

Answer: XH × Xh

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

XhXh, XhY, XHXh, XHY

Find the cell

XH × Xh = XHXh

Answer

Cell XH × Xh → XHXh
2.Genetics

Answer: Ab × Ab

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.

Genotype asked for

AAbb

Gametes

A homozygous genotype needs the same gamete from both parents, so only one cell in the 16 fits.

Ab × Ab = AAbb

Answer

Cell Ab × Ab → AAbb
3.Cell biology

Answer: B · 2 ATP

Why this is the answer

Glycolysis uses 2 ATP and produces 4, a net gain of 2 ATP, plus 2 NADH and 2 pyruvate per glucose.

Answer

B · 2 ATP
4.Cell biology

Answer: C · In mitochondrial DNA

Why this is the answer

Mitochondria, and their DNA, are inherited almost only from the egg. Mitochondrial disorders therefore follow maternal inheritance.

Answer

C · In mitochondrial DNA

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