sexually produced organisms vary in characteristics because meiosis which produces gametes fuse to give a sexually produced offspring.
Meiosis causes variation through :-
- crossing over - homologous chromosome pair along their length gene by gene. - Breaks occur along the chromosomes and they rejoin trading some of their genes
NB crossing over in prophase I
--------------------------------------------------------------------------------
- Independent assortment - chromosomes randomly move to separate poles during meiosis I. - Each gamete will have different combination of chromosomes and contain a mixture from both father and mother
--------------------------------------------------------------------------------
- Segregation of sister chromatids in Anaphase - often one chromatid is a mixture of paternal and maternal DNA while other chromatid is not
---------------------------------------------------------------------------------
- Random fertilization - each gamate contains a different set of DNA. - any male gamete will fuse with any female gamete so each offspring will be genetically different which cause variation
