Mendel and Morgan- Genetic Pioneers

A. Introduction

B. The Life of Gregor Mendel

Statue of Gregor Mendel on the grounds of the Augustinian Abbey, Brno, Czech Republic

Mendel's garden on the abbey grounds where experiments in pea genetics were done.

C. Why peas?

• Flower structure
• pollination and fertilization
• the offspring of peas

D. The Classical Experiments of Mendel

• The method for the genetic cross
• what types of pea plants did Mendel work with? example, flower color

• What is a parental strain?
• Mendel's First Experiment
• What is the F1 generation?
• What is a dominant trait?
• Mendels Second Experiment
• What is the F2 generation?
• What is a recessive trait?
• Mendels Explanation of the data: 

1) Hereditary characters were transmitted from parent to offspring by discrete factors (now called genes). 

2) The factors exist in alternate forms (now called alleles): recessive and dominant

3) Each pea “parent” had a pair of factors, one originally obtained from each parent

4) During sexual reproduction, the factors separate (or segregate) to produce pollen and/or egg cells (that is, each gamete contains only 1 factor). This is called Mendel’s Law of Segregation.   

5) The expression of a given trait depends on the specific combination of recessive and dominant factors. The dominant trait will be expressed if both factors are dominant or if one factor is dominant and the other recessive. The recessive trait is only expressed if the factors received from both parents are recessive.

• What are homozygous alleles?
• What are heterozygous alleles?
• The Punnet Square

• The dihybrid cross
• Mendel's Principle of Independent Assortment
• Explanation of Independent Assortment Using Chromosomes in Meiosis  

E. Modifications to Mendel

1. Implication from Mendel?

• Polygenic Inheritance (height genes; skin pigmentation)

2. Incomplete Dominance

-snapdragons

3. Multiple alleles and codominance

-Human blood groups

4. Epistasis

-flower color

5. Effect of environment

6. Sex Linkage and T.H. Morgan

• the fly (Drosophila melanogaster)
• why do you need mutant flies?
• The eye color experiment

from: http://www.exploratorium.edu/exhibits/mutant_flies/white-eyes.gif

• Why are there no white eyes females in the F2 as predicted by Mendel?
• Answer of Morgan:

The gene for eye color was linked to the "X" chromosome, "Y" chromosome carries no information for eye color:

    Female flies XX

    Male flies  XY

• Other sex-linked traits