Biology · MU Pleven

6. Structure of eukaryotic chromosomes. Karyotype. Methods of cytogenetic analysis.

Covers the organisation of eukaryotic genomes and chromatin, from nucleosome packing and the levels of DNA folding through to loop domains anchored at MARs/SARs. It then describes chromosome structure, centromeres and telomeres, and the centromere-based classification into metacentric, submetacentric, acrocentric and telocentric types. The human karyotype, chromosome groups A to G, and the G, Q, R and C banding methods are set out next, followed by FISH and comparative genomic hybridization for cytogenetic analysis.

Inside: 17 sections · 6 labelled pictures · 26 flashcards · 4 min

Topic 6 of 63 in the MU Pleven syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 17 sections, about 543 words (4 min of reading), with 26 flashcards.

In this note

  1. Structure of eukaryotic chromosomes. Karyotype. Methods of cytogenetic analysis.
  2. EUKARYOTIC GENOME & C-VALUE
  3. EUKARYOTIC GENE ORGANIZATION
  4. CHROMATIN & NUCLEOPLASM
  5. PACKING OF DNA INTO METAPHASE CHROMOSOMES
  6. LEVELS OF DNA PACKING
  7. FUNCTIONS OF MARs/SARs
  8. CHROMOSOME STRUCTURE & FUNCTION
  9. CONDENSATION & CHROMOSOME TERRITORIES
  10. CHROMOSOME CLASSIFICATION BY CENTROMERE POSITION
  11. HUMAN KARYOTYPE
  12. Chromosome groups A–G:
  13. KARYOTYPING & BANDING TECHNIQUES
  14. CENTROMERES & TELOMERES
  15. OTHER CHROMOSOME FEATURES
  16. MOLECULAR CYTOGENETICS — FISH
  17. COMPARATIVE GENOMIC HYBRIDIZATION (CGH)

EUKARYOTIC GENOME & C-VALUE

  • Eukaryotes have a diploid number of chromosomes.
  • Genome = genetic information in one complete haploid set.
  • C-value = total amount of DNA in the haploid genome.

EUKARYOTIC GENE ORGANIZATION

  • Typical eukaryotic gene consists of:
  • Exons → sequences present in mature mRNA.
  • Introns → intervening, non-coding sequences.
  • Regions between genes may regulate chromatin structure or contain promoters.
  • Eukaryotic genes may form clusters, but are independently regulated.
  • No operons / no polycistronic mRNA in eukaryotes (unlike prokaryotes).
  • Prokaryotes often regulate multiple genes through a single control element.

Chromosomes store and organise the organism’s genetic information.

  • Allow condensation of DNA so it fits inside the nucleus.
  • Ensure hereditary information is transmitted to offspring.
  • Each species has a specific chromosome number.
  • Humans: 46 chromosomes (somatic cells), 23 in gametes.

CHROMATIN & NUCLEOPLASM

  • Chromatin = DNA + associated proteins.
  • Stored in the nucleoplasm (gel-like nuclear interior).
  • Forms the material that makes chromosomes.
  • Prokaryotes: DNA is a single circular chromosome.
  • Eukaryotes: DNA arranged in multiple linear chromosomes.
  • Each eukaryotic species has a fixed chromosome number in body cells.

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