The cell cycle and cell division

The cell cycle and cell division

Chromosome structure

Chromosomes are made of DNA and a protein called histone. DNA is a double helix, which runs the length of a chomosome and sections of this are called genes.

DNA > Chromatin > Chromosomes#

Chromosomes are only visible when chromatin condesnes prior to cell divison. This is after each DNA molecule has made an exact copy of itself. The two copies of a chromosome are called sister chromatids. They lie parallel along their length joined at a region called the centromere. Pairs of matching chromosomes are called homologous pairs.

Ploidy level and chromosome number

• Different species have different numbers of chromosomes in their cells.
• Normal human body cells have 46 chromosomes (eggs have 23, sperm have 23) 
• The number of chromosomes in a complete set is the haploid number, n  (n=23)
• Humans recieve one complete set of chromosomes from each parent and have two sets of chromosomes, known…