Lecture 3
Basic Principles of Inheritance

Old notions of inheritance
	Blending- as in skin color
	Problems for Natural Selection
		Hybridization of types
		Loss of variation
Gregor Mendel (1822-1884) & the discovery of the laws of heredity
	Background
		Austrian rural peasant family- very knowledgable about plants
		Smart kid- entered monastery to further education
		Stunk at parish work- too empathetic
		Became teacher- a natural
		Went to get teacher's certificate- failed exam when disagreed with one 
		    answer vehemently
		Decided to prove examiner wrong
	Mendel's pea plants 1857-1865
		Controlled breeding & extensive records
		Tracked simple traits
			7 pairs of traits
			None linked
		First bred pure plants
		Next cross-bred different varieties
		Traits disappeared in first generation
		Cross-bred those & traits reappeared
		3:1 ratio in traits
		Why is this important?
			Traits endure
			Variation maintained
	The laws of heredity
		The infamous Punnett Square
		Particulate inheritance
		Law of Segregation
		Law of Independent Assortment
		Dominant & Recessive
	Forgotten and rediscovered
		Paper published in 1866
		No-one understood it; was ignored
		Re-discovered in 1900 by 3 separate botanists; de Vries, Correns, & 			   Tschermark
Chromosomes, Genes and mutations
	First came discovery of cell, nucleus (1820's) & cell division (mitosis)
	Chromosomes found in 1870's
		Duplicate & divide to create new cells
		Each species has set number- 46 for humans
		Come in pairs; one of each pair from each parent- Homologous 				   Chromosomes
		Sex cell division produces gametes with 1/2 number (meiosis)
			First homologous pair off then divide
			Then duplicate & divide to produce gametes
	Mutations
		Hugo deVries- 1890's
			Studied primroses looking for source of variation
			Discovered "new" traits- mutations
			Closing in on Mendel's Laws when discovered Mendel's work
			Called units of inheritance "pangens" later contracted to "genes"
	Genes- term coined in 1909
		By 1880's, people suspect that chromosomes made up of smaller 				    bits that controlled for certain structures
		T. E. Morgan
			Professor at Columbia, fascinated by thought of mutations
			Decided to work with fruit flies
			First mutation discovered in 1910- White eyes
			Further work (& more mutations) proved that genes existed
		Important concepts
			Alleles- different types of the same gene
			Genotype- genetic constitution
			Phenotype- physical expression
			Homologous Pair- both genes on homologous chromosomes
			Homozygous- Homologous Pair with same allele
			Heterozygous- Homologous Pair with different alleles
			Monogenetic- a trait that is controlled by one gene location
			Polygenetic- a trait that is controlled by several gene locations