Genetic Variation & Control

Genetic Variation & Control

1. A nucleus of a cell contains chromosomes which is made up of DNA

   • A section of DNA is called a gene
     • Carry information that control the characteristics of an organism, different genes control the development of different characteristics
     • During reproduction, genes are passed from parent to offspring (they are inherited)

2. Inheritance of genes

   • Male gamete: Sperm
   • Female gamete: Egg
   • At fertilization genes carried by the egg/sperm are mixed to produce a new individual. (Fusing of the nuclei)
     • This mixing is completely random so produces lots of variation, even among offspring from same parents.
   • 23 pairs of chromosomes in an adult cell

3. Sexual/Asexual reproduction

   • Sexual
     • Genes from egg and sperm fuse together and produce a new individual
       • Contains genes from both parents so you have characteristics from both.
   • Asexual
     • One parent is needed
       • DNA will be genetically identical so there will be no variation i.e. cloning
     • E.g. bacteria, fungi, identical twins
   • sexual: if there was a disease and there was no variation between species then they would be wiped out
   • asexual: if there is only one organism left then they can repopulate

4. Meiosis

   • Gametes are formed from cells in the reproductive organs by a type of cell division called meiosis.
   • The cells that are formed by meiosis have half as many chromosomes as the cell that formed them
   • Main features: the chromosomes are copied and the cell divides twice, forming four gametes