Mendelian genetics

Early beliefs Pangenesis – males and females formed genes in every organ, genes were carried via blood to genitals into children (Hippocrates, Aristotle) Epigenesis – embryo was preformed in the sperm; females ‘grew’ the embryo Blending theory – offspring gets a blend of parent characteristics

And then came Gregor Mendel A monk who lived in Austria in the mid 1800s Researched the common pea plant between 1856 and 1863 (studied about 10,000)

Why pea plants? - easily available, easy to grow, mature quickly -Different varieties had different traints -Each trait only had two variations -Flowers were self-pollinating

Mendel’s experiments Crossed two purebred parents (P generation) (one short and one tall) BIG SURPRISE!! All offspring (F1)were tall (blending theory did not hold) Crossed F1 generation amongst themselves RESULT: original traits displayed in 3:1 ratio

Fundamental Laws of Genetics 1)The Law of Segregation: Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization. (meiosis was discovered 25 years later )

2) The Law of Independent Assortment: Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.

Mono- and di- hybrid crosses Monohybrid – a cross of parents with differing forms of only one gene (alleles) (wrinkled and round peas) Dihybrid – a cross that involves two genes with contrasting alleles (shape (wrinkled and round)and colour (yellow and green))

3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.