3.4.1 DNA, genes and chromosomes

Question 1

What is the structure of chromosomes?

Answer 1

• A Chromosome is one long piece of DNA found in the nucleus

• Chromosomes are only visible when the cells are dividing (from prophase onwards).

• DNA is wrapped around histone proteins forming nucleosomes - these coil up further to form chromatin.

• These nucleosomes then condense tightly during mitosis (and meiosis).

• Telomeres at the ends of the
chromosomes are repetitive DNA - they offer protection against degradation.

Question 2

What are homologous chromosomes?

Answer 2

Chromosomes with the same shape and size with the same genes but different alleles.