Genetics A. The work of Gregor Mendel 1. Monohybrid crosses 2. Dominant and recessive alleles 3. Law of Segregation B. Mendel and meiosis

Who was this Mendel and what the heck is he doing in a monastery? born in 1822 trained himself to be a naturalist early in life worked as a substitute science teacher failed the qualifying exams to be a regular high school teacher! joined a monastery in Brunn, Austria sent to Vienna U. to study science and math

MendelWeb Mendel’s first published work: "Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight! Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!!

The work of Gregor Mendel worked with pea plants… …he called them his children! Why pea plants??? There was a long-standing tradition of breeding pea plants at the monastery where Mendel lived and worked

So…they were readily available and they come in lots of varieties! …there were plants with different flower colors, seed color, flower position etc..

‘Brother Greg... We grow tired of peas again!!!’

And best of all… Pea plants flowers can reproduce by themselves This allowed Mendel to see if strains were true breeding and to produce hybrids

How Mendel made hybrids… He’d then tie little bags around the flowers to prevent contact with stray pollen.

Mendel’s hybridization experiments… Monohybrid crosses: Parental Generation True-breeding purple flower True-breeding white flower x All purple flowers (the hybrids) F1 generation Allowed F1 offspring to self-fertilize F2 generation 705 purple 224 white

The results of Mendel’s monohybrid crosses led him to propose… All organisms contain two “units of heredity” for each trait (alleles). Dominant and recessive alleles… …and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive). The Law of Segregation – during gamete formation, alleles separate randomly into separate gametes.

A bit of genetic jargon… phenotype vs. genotype What the organism looks like What alleles the organism has - its genetic makeup

More jargon… homozygous vs. heterozygous P 2 of the same alleles: PP or pp 2 different alleles: Pp p

A Punnett square

A Punnett square… Gametes from one parent p P PP Pp P Gametes from other parent purple purple pp Pp p purple white Ratio: 3:1 or ¾ purple, ¼ white