cells and chromosomes

• chromosomes are made of DNA and a protein called histone
• chromosomes only become visible when chromatin condenses during interphase, after each DNA molecule has replicated - the two copies are called sister chromatids
• sister chromatids lie parallel to each other and are held together by the centromere
• humans have 23 pairs of chromosomes, 46 in total
• the number of chromosomes in a complete set is the haploid, humans receive on on set from each parent and so the chromosomes occur in matching pairs
• matching pairs of chromosomes are called homologous pairs