Mendel and Genetics

Brother Gregory speaks to his class,

The subject for today's lesson is the nature of plant hybridizations, or how I discovered the new science of genetics! You must follow this lesson, carry out some of my famous genetic crosses using pea plants, and try to answer the questions.

"Let us begin .......

"It all began in my monastery garden late one summer, when I noticed that not all the pea plants I was growing looked the same.

peas -|- differences -|- idea -|- flowers
fertilization -|- artifical -|- blending -|- one trait

traits -|- genetic cross -|- round two

"Some had flowers that were one color and some had flowers that looked completely different , also, some grew tall (almost as big as me!) while others were much shorter, hardly coming up to my knees. These characteristics seemed to come in pairs. I was wondering why this should be so, when suddenly I got an idea.

"The flowers were known to be the reproductive structures of the plant, and somehow produced the seeds that in turn gave rise to the next generation of pea plants.

"But, before seeds formed, pollen from one flower had to be moved to a different flower by insects, birds or the gardener who was trying to grow a better crop of peas.

"It was thought that both parents gave something to seed during this process and most believed that two fluids blended together in a way that gave rise to an offspring that was a combination of characters, or a mixture of characters from both parents - just as if two cans of paint had been mixed together.

"I decided to test this by performing a series of experiments in which one pea plant was hybridized with a second pea plant. I would first identify a set of stable characters, or traits, that were cleanly and clearly inherited, then I would hybridze the plants together and follow what happen to each individual trait, one at a time, to see if there were any consistent patterns of inhertiance that I could interpret.

traits -|- genetic cross -|- round two

A Genetic Cross - how the hybridzations were performed - and why.

"Every spring I go out into the garden and begin my experiments in plant hybridizations, which use as their starting material Pisum sativa - the common pea plant.

"I have collected a range of different types of pea plants, which I hope are all the same species, However, the art of classification is not perfected yet, so there is some doubt on this issue.

"This is where you do get your chance to repeat my work and discoveries. Begin by reading the backgound material, which is an introduction to the ideas and process I once used.

Performing a Genetic Cross
an introdution to the ideas and the process


"So, how did it go?

"Did you find out how a genetic cross is performed?

"However, before going any further, it is important to realize that good, scientific experiments need to be carefully controlled so as to prevent mistakes or errors mixing up the results and your conlcusions.

"Now it is time to find out something about the traits and plants we will be using in these crosses.

Pure Breeding - the consistency of the material

"This is where I began to develop my ideas concerning the atomistic nature of the controlling principals that were producing the traits we see in these plants.

"Before you can start helping me with my experiments in plant hybridization, you must first investigate the Pisum sativum plants that I have given you. These plants are your starting material. You must find out which of these plants, and which of their traits, you can trust.

Performing a Genetic Cross: #2
pure breeding and consistency of the material

"Any parent plant(s) that consistently give only one type of offspring in your experiments can be called pure breeding which strongly implies that they are carrying pure controlling elementes and of only one kind.

"Which traits of these pea plants are consistently pure breeding? These are the ones we will need for future experiments.

blending inheritance

Blending or Not - do traits blend or remain separate as they are inherited?

"I want you now to investigate the properties of the Pisum sativum traits and find out if alternative versions of a trait blend together in an offspring, or if the different forms of a trait remain independent and distinct.

"Once in the body of the offspring plant, the elementes direct the development of the traits they control. There are two possibilities for what happens next and you must eliminate one of the options.

"One very old idea is that traits blend like cans of paint. The other option is that each trait remains intact and distinct. You must carry out the next set of experiments to determin which is the case.

Performing a Genetic Cross: #3
do traits blend in the offspring, or not?

genetic cross -|- round two
combinations -|- dominant -|- patterns

Patterns of Inheritance - one trait inherited for two generations

"I now want you to investigate the patterns of inheritance seen in your pea hybrids as the traits are inherited through two generations. These generations are called the first filial or F1 and the second filial or F2 generations.

"If I am right, and the form of a trait is controled by a transmission elemente, then an offspring recieves one elemente from its male parent and a second elemente from its female parent.

"Once in the body of the offspring, these elementes direct the development of the traits they control. It should be possibile to determin what elementes each offspring inherits by the numbers, and ratios, of the offspring showing those traits.

Performing a Genetic Cross: #4
what are the patterns and what do they mean?

results -|- data -|- publication

genes -|- patterns
combinations -|- results -|- ratios

interpretation -|- consequence


"What kind of results did you get?

"In all of these experiments you are collecting raw data and then trying to find patterns that can be interpreted, however, the interpretation of raw data has to be done very carefully.


"Every time you perform one of these experiments and gather data, the raw numbers will be different, and on their own hard to interpret. However a simple mathematical calcultion suddenly puts it all into perspective.

"A ratio between two numbers of pea plants becomes a consistent value if there is an unseen force directing the outcome. The actual numbers are simply a reflection of an underlying principal which the ratio between them reveals.

What it all means

"The ratio between these two numbers gave me a clue. There were two elementes (later called 'genes') in each pea plant for each of the traits I was studying, and they came in two different forms - which I called dominant and recessive. A plant could have any combination of these two 'genes' and this combination would determine the appearance of that trait.

"At the time of reproduction, each parent plant donated only one of these 'genes' to either its pollen grain or its egg cell. During fertilization and seed formation, these donated genes were reunited and helped create the next generation of plants. I had discovered the secret of inheritance!

"I later published my findings in a local scientific journal and sent copies to all my scientific friends and any one whom I thought would be interested, but none of them followed up my work or tried to repeat my hybridizations or results.

traits -|- genotype -|- combinations -|- dominant
patterns -|- haploid and diploid -|- genetic cross
genetic cross round two -|- ratios -|- results

interpretation -|- consequence

peas -|- differences -|- idea -|- flowers
fertilization -|- artifical -|- controls -|- blending -|- one trait
blending inheritance -|- results -|- statistics -|- publication
classification -|- species problem

Science@a Distance
© 2004, Professor John Blamire