Mendel & Heredity
Chapter 11.1
The Origins of Genetics
Heredity
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The passing of traits from parents to
offspring is known as heredity.
What are some examples of traits that
are passed from your parents?
Even before the structure of DNA was
discovered people were interested in
how genes on DNA were passed from
generation to generation.
Gregor Mendel
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Gregor Mendel was an Austrian monk born
in 1822.
Mendel is known today as the father of
modern genetics.
Mendel performed experiments on
different varieties of pea plants.
Mendel used pea plants because there are
many different traits, they grew quickly
and they can self-pollinate.
Seven traits Mendel
studied
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Flower color – (purple & white)
Seed color – (yellow & green)
Seed shape – (round & wrinkled)
Pod color – (green & yellow)
Pod shape – (smooth & wrinkled)
Flower position – (middle & top)
Plant height – (tall & short)
Mendel’s Observation
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Mendel’s first observation came from a
monohybrid cross a cross that involves
one pair of contrasting traits.
For example crossing a plant with purple
flowers with one with white flowers.
In order to make sure he had truebreeding purple & white plants Mendel
self-pollinated each for many generations.
Three Steps of Mendel’s
Experiments.
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Step 1: Mendel crossed the two
different true-breeding plants & called it
the P (or parental) generation.
Step 2: The offspring from the P
generation were then crossed and called
the F1 Generation.
Step 3: The offspring from the F1
generation were then crossed and called
the F2 Generation.
Mendels Results
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After the P generation was crossed
Mendel noticed that all of the offspring
exhibited one type of color, the other
color “disappeared”.
In the F2 generation the color that
“disappeared” came back in a ratio of
about one in every four.
Calculating Mendel’s
ratios.
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Mendel noticed that he had 705 purple
flowers and 224 white flowers in his F2
generation.
705/224 = 3.15
224/224 = 1
A ratio of about 3:1
Do your own: 787 tall plants & 277 short.
Review Questions
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Why did Mendel use pea plants?
What was the ratio Mendel noticed in
his F2 generation?
What is the following ratio of pod color
428 green & 152 yellow.
How did Mendel make sure that his P
generation were true-breeding?