Summary and Exam Tips for Chromosome
Chromosome is a subtopic of Genetics, which falls under the subject Biology in the IB DP curriculum. Prokaryotes have a single, circular DNA molecule as their chromosome, which is not associated with proteins, hence termed "naked." Some prokaryotes also contain plasmids, small circular DNA rings that can carry genes like those for antibiotic resistance. In contrast, eukaryotic chromosomes are linear and associated with histone proteins, forming a complex structure. Eukaryotes have multiple chromosomes, each carrying different genes at specific loci. Homologous chromosomes in eukaryotes carry the same genes but may have different alleles. Diploid nuclei contain pairs of homologous chromosomes, while haploid nuclei have one chromosome from each pair. The number of chromosomes is a species-specific characteristic, affecting interbreeding capabilities. Karyograms visually represent chromosomes in homologous pairs, aiding in sex determination and diagnosing conditions like Down syndrome. Sex chromosomes (X and Y) determine sex, while autosomes do not. Techniques like Cairns’ autoradiography have advanced our understanding of chromosome structure and replication.
Exam Tips
- Understand Key Differences: Be clear on the differences between prokaryotic and eukaryotic chromosomes, especially regarding structure and association with proteins.
- Memorize Definitions: Know the definitions and characteristics of terms like plasmids, diploid, and haploid nuclei.
- Use Visual Aids: Familiarize yourself with karyograms and how they are used to determine sex and diagnose genetic conditions.
- Practice Comparisons: Be prepared to compare chromosome numbers and genome sizes across different species.
- Focus on Applications: Understand practical applications like Cairns’ autoradiography technique and how it supports theories like semi-conservative replication.
