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1.6.4Inquiry Process

Genomes — IB Biology HL Revision Notes & Topical Questions

5 min read 5 parts Lesson 18 of 160

📚 IB Biology HL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Part 1 of 5What a Genome Is

Genome
  • Genome The complete set of genetic information of an organism, including all of its chromosomal DNA.
Base sequence
  • Base sequence The order of A, T, C and G along DNA, which is unique to each species and differs slightly between individuals.
Nuclear genome
  • Nuclear genome DNA in the nucleus, which in humans is about 3.1 billion base pairs spread across 46 chromosomes.
Organelle genomes
  • Organelle genomes Mitochondria and chloroplasts have their own small circular DNA, inherited separately from nuclear DNA.
Genes
  • Genes Segments of DNA coding for polypeptides or functional RNA, forming only part of the genome.

Part 2 of 5Genome Features

Genome Features
Coding DNA
  • Coding DNA Sequences that code for polypeptides make up only about 1 to 2 percent of the human genome.
Non-coding DNA
  • Non-coding DNA Includes introns, regulatory sequences, and repeated sequences that are not translated.
Variation
  • Variation Individuals differ at roughly one base in every thousand, mostly single nucleotide polymorphisms.
Prokaryote genomes
  • Prokaryote genomes Smaller, with little non-coding DNA, so most of the sequence codes for proteins.
SpeciesGenome sizeApprox. genes
E. coli4.6 Mb4300
Homo sapiens3100 Mb20 000

Part 3 of 5Human Genome Project

1
The international project began in 1990 with the aim of sequencing all the bases of the human genome.
2
DNA was cut into fragments, sequenced, and then assembled into continuous chromosome sequences by computers.
3
A working draft was published in 2001 and the project was declared essentially complete in 2003.
4
It revealed that humans have about 20 000 protein-coding genes, far fewer than expected.
5
The data are freely available and enable research into disease, evolution and personalised medicine.

Part 4 of 5Worked Example

Question

  • The human genome is about 3.1 × 10⁹ base pairs and contains roughly 20 000 protein-coding genes.
  • Estimate the average number of base pairs per protein-coding gene, and comment on the result.

  1. Divide total base pairs by number of genes: 3.1 × 10⁹ ÷ 2 × 10⁴.
  2. 3.1 × 10⁹ ÷ 2 × 10⁴ = 1.55 × 10⁵ base pairs per gene.
  3. This is far larger than a typical gene, because most of the genome is non-coding DNA such as introns, regulatory sequences and repeats.

Answer About 155 000 base pairs per gene, showing that most human DNA does not code for protein.

Part 5 of 5Exam Checklist & Tips

1.6.4 – Key Points for the Exam

  • Genome All the genetic information of an organism.
  • Gene A heritable sequence coding for a polypeptide or functional RNA.
  • Base pair Two complementary nucleotides joined by hydrogen bonds.
  • SNP A single base difference between individuals.

Common Mistakes

  • Saying the genome is only the genes; it includes non-coding DNA.
  • Using genome and chromosome as synonyms.
  • Stating that humans have the largest genome of any organism.
  • Forgetting mitochondrial DNA is part of the cell genome.

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