The cell cycle and cell division

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  • Created by: zoolouise
  • Created on: 07-04-16 20:04

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#

(http://oerpub.github.io/epubjs-demo-book/resources/0321_DNA_Macrostructure.jpg)

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.

(http://www.clt.astate.edu/mhuss/chromosome.jpg)

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…

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