Gregor Mendel

GREGOR MENDEL

The Ferdinand Magellan of Genetics

Quick QuestionChallenge:

Who was Gregor Mendel, and what did he do?

Gregor Mendel was an Austrian monk who discovered the basic tenets of genetics through

breeding experiments with peas.

Quick review: Sexual reproduction in plants

Mendel’s first cross: two true-breeding parents

What do you think the hybrid offspring looked like?

Results of the first cross:

They were all tall! Why? Some genes (like the one for plant

height) have two contrasting forms, called alleles.

Mendel determined that the allele for shortness was completely masked by the presence of the allele for tallness.

In other words, Tallness (T) is dominant and shortness (t) is recessive.

He found this principle of dominance to be true for many other pea traits, too!

You decide what’s dominant

GENE Plant heightDominant allele Tall (T)Recessive allele Short (t)

Mendel’s F1 cross

Will all the offspring of this generation be tall, too?

No!

How did short plants reappear?

When sex cells (or gametes) form, alleles must separate (or segregate) from each other so that each sperm and each egg only has one allele.

When fertilization occurs, the alleles recombine randomly.

If two recessive alleles pair up, the recessive trait will now be shown!

Let’s act out Mendel’s crosses to see how this

happens…

Who wants to be a gamete?

TWO TASKS:

1. Grab a laptop and complete the WebLab in today’s daily agenda

(accessible from Moodle)

2. Upon completion of the WebLab, start your homework

assignment, which is due tomorrow.