Mendel and his Peas
Chapter 5 Lesson 1
Chapter 5: Genetics
How are traits passed
from parents to
offspring?
Mendel and his Peas
• Why did Mendel perform crosspollination experiments?
• What did Mendel conclude about
inherited traits?
• How do dominant and recessive
factors interact?
Gregor Mendel
the father of genetics
Genetics
the study of how traits are
passed from parents to
offspring
(the study of inheritance)
Heredity
the passing of traits from
parents to offspring
Trait: a genetically determined
characteristic or condition
Gregor Mendel
Mendel's work was
done about 140 yrs.
ago, but even now
much of what we
know about
genetics is based
on Mendel's work
and illustrated by it.
Gregor Mendel
was born in 1822 on a farm in
Heinzendorf, Austria
At age 21 entered the
Augustinian order of the Roman
Catholic Church
As a monk he - studied science
at the University of Vienna and
became an excellent
mathematician
Gregor Mendel
As a school teacher - he engaged in
many scientific activities
At a monastery - he began a
program of selective breeding of
peas. After 8 yrs. of raising 30,000
pea plants and recording and
classifying many pages of notes, he
wrote a paper with his conclusions
called Mendelian Genetics (1865).
Mendel’s Experimental Methods
Mendel studied genetics by doing
controlled breeding experiments with
pea plants.
There are two types of pollination:
• self-pollination
• cross-pollination
Self-Pollenation
Mendel’s Experimental Methods
When a true-breeding (purebred) plant
self-pollinates, it always produces
offspring with traits that match the
parent.
Mendel crosspollinated pea
plants himself
and recorded
the traits that
appeared.
Cross-Pollenation
Mendel’s Experimental Methods
Why did Mendel perform crosspollination experiments?
Mendel’s Results
Once Mendel had enough truebreeding plants for a trait he
wanted to test, he cross-pollinated
selected plants.
Plants are called hybrids if they
come from true-breeding parent
plants with different forms of the
same trait.
First-Generation Crosses
Mendel’s Results
hybrid
Science Use the offspring of two
animals or plants with different forms of
the same trait
Common Use having two types of
components that perform the same
function, such as a vehicle powered by
both a gas engine and an electric motor
Mendel’s Results
Mendel also cross-pollinated hybrid plants.
He observed that offspring of hybrid
crosses always showed traits in a 3:1 ratio.
Second-Generation
(hybrid) Crosses
Mendel’s Results
Mendel recorded traits
of offspring from many
hybrid crosses.
Mendelian Genetics
His paper was the first recorded
study of how traits pass from one
generation to the next.
Mendel also was the first to use the
mathematics of probability to explain
heredity.
Mendelian Genetics
When Mendel's paper was published, in
1865, it received little attention, and was
rarely cited by botanists or biologists
during the next 34 years.
In 1900, Mendel's work was cited by
three botanists, writing in different parts
of Europe: Hugo de Vries, in
Amsterdam; Carl Correns, in Tübingen;
and Eric Von Tcshermak, in Esslingen,
Austria.
Mendel's Theories
the concept of unit
characteristics
the concept of dominant and
recessive
the concept of segregation
the concept of
unit characteristics
Mendel concluded that two factors, one
from the sperm and one from the ovum,
control each inherited trait.
if factors were the same - purebred
TT (tall) tt (short)
if factors were not the same - hybrid Tt (tall)
The Concept of
Dominant and Recessive
Dominant trait - a genetic factor that blocks
another genetic factor.
Recessive trait - a genetic factor that is
blocked by the presence of a dominant
factor.
The dominant allele (factor) completely
masks the presence of the recessive allele
(factor).
the concept of
segregation
Mendel reasoned that when a cell
forms gametes, the genes separate
(segregate) so that there is only 1
gene for each characteristic in each
gamete.
Principles of Heredity
1. Traits are controlled by alleles on
chromosomes.
2. An allele’s effect is dominant or
recessive.
3. When a pair of chromosomes
separates during meiosis the
different alleles for a trait move into
separate sex cells.