April 2008

Mendelian GeneticsMendelian Genetics

March 6, March 6, 20092009Mr. Mr. BromwellBromwell

GeneticsGenetics – the scientific study of heredity.– Studied for centuries• Artificial selection (i.e. breeding)• Domestication

– Blending hypothesis• Could not account for unexpected traitstraits

A traittrait is a characteristic that can be passed from parent to offspring.

Gregor Johann MendelGregor Johann Mendel(1822-1884)

• 1822 - Born in Heizendorf, Austria

• 1843 - Enters monastery• Studied physics, math,

chemistry, botany, paleontology, & plant physiology

• Fails professorial exam • 1860s – returns to

monastery – Studies inheritance of traits

in pea plants.– Uses 20,000 plants– Refutes blending hypothesis

Why Peas?Why Peas?• Mendel choose peas

because… … they are easy to grow. … they reproduce rapidly.… they were readily available.… the structure of pea flower

enabled him to control fertilization.

… they possessed distinctive traits that could be easily distinguished.

The Sex Lives of PeasThe Sex Lives of Peas

The Sex Lives of PeasThe Sex Lives of Peas

• Pea plants usually reproduce by self-fertilizationself-fertilization.– leads to “true-breeding” or

“pure-breeding” plants

• Mendel could easily cross-cross-pollinatepollinate pea plants by hand.– can result in “hybrids”

Pea flower

Mendel’s ExperimentMendel’s Experiment

x

Mendel’s HypothesisMendel’s Hypothesis1. Each trait is controlled by a ‘factor.’– since there were two distinct traits possible, there

must be two distinct factors– ‘factor’ is called an alleleallele – alternative forms of a

single genegene, or region of a chromosome that codes for a trait.

2. Alleles are paired in each plant.3. If an organism has two different alleles for a

trait, only one is shown.– dominant allele dominant allele – fully shown (expressed)– recessive allele recessive allele – masked by the dominant allele

ReferencesReferencesBiggs, Alton, et. al. Biology. New York: The McGraw Hill Companies, Inc., 2007. Fairholm, Rebsie. "Daughter of the Soil." [Weblog How to breed your own garden peas]

20 May 2007. 2 Apr 2008 <http://daughterofthesoil.blogspot.com/2007/05/how-to-breed-your-own-garden-peas.html>.