MENDELIAN GENETICS Meet Lucy and Maria Aylmer twins

MENDELIAN GENETICS

Meet Lucy and Maria Aylmer, twins from the UK. Lucy and Maria have the same parents. Initial Idea: Explain in your own words how is this possible?

The story of Gregor Mendel 1822 -1884

• Born 1822 in Heizendorf • Peasant farmer parents • Great promise as a student • Post-secondary studies at the University Philosophical Institute in Olmutz • Plagued by ill health • “unstable psychological constitution” • Became a monk in 1843 in Brno to be free from what he describe as “the bitter struggle for existence”

Franz Unger • Studied at the University of Vienna under Professor of Plant Physiology Franz Unger. • Unger rejected the established idea of the time that species were stable. • Proposed that variations arise in natural populations. • Suggested that large variations form specific differences in species. • Shift from “preformation” to blending in the scientific community.

Timeline • Comte de Buffon (1707 -1788): experiments in hybridization with animals (from other people reports). Concluded that offspring inherit the extremities of their body from their sires and their internal parts, shape and size from their mothers.

It took time for plants to be used in hybridization experiments. “What man will ever believed that God Almighty should have introduced such confusion, or rather such shameful whoredom, for the propagation of the reign of plants. Who will instruct young students in such a voluptuous system without scandal? ” J. G. Siegesbeck, Professor of Botany at St. Petersburg

• Father of classification • Made the plants sexual organs the basis for his system of classification • Concluded that any plant showing a combination of characteristics from those of two known species must be an hybrid. • Did not test for purity of type. • “Two Layer theory of heredity”: outer layer (leaves and rind of the stem) inherited from father, and inner layer inherited from mother. Carl Linnaeus (1707 -1778)

Mendel’s ideas • Summer 1856 • First tested 34 varieties of pea plants for purity of type • Was interested in understanding the mathematical relationships of the various hybrid offspring. • Between 1856 and 1865: 29, 000 plants.

• Crossed purple and white flower plants (P generation) • Offspring were always purple (F 1 generation) • Crossed F 1 to F 1 • Offspring were mixed purple and white (F 2 generation) averaging a 3: 1 ratio purple to white. • Many more experiments with many other traits. • Invented the idea of “factors” to explain the results.

• Law of segregation: every individual possesses a pair of alleles(assuming diploidy) for any particular trait and that each parent passes a randomly selected copy (allele) to its offspring. • Law of independent assortment: separate genes for separate traits are passed independently of one another from parents to offspring.

• Published in 1866 • Not widely read or accepted • No actual evidence for the “factors” • No statistical analysis available • Died in 1884 of kidney failure (62 years old) • Work not recognized for another 34 years.