Download Gregor Mendel and Introduction to Genetics

Gregor Mendel and Introduction to Genetics
For thousands of years farmers and herders have been selectively
breeding their plants and animals to produce more useful hybrids. It
was somewhat of a hit or miss process since the actual mechanisms
governing inheritance were unknown. Knowledge of these genetic
mechanisms finally came as a result of careful laboratory breeding
experiments carried out over the last century and a half.
By the 1890's, the invention of better microscopes allowed biologists to
discover the basic facts of cell division and sexual reproduction. The
focus of genetics research then shifted to understanding what really
happens in the transmission of hereditary traits from parents to
children.
A number of hypotheses were suggested to explain heredity, but Gregor
Mendel, a little known Central European monk, was the only one who
got it more or less right. His ideas had been published in 1866 but
largely went unrecognized until 1900, which was long after his death. His early adult life was spent
in relative obscurity doing basic genetics research and teaching high school mathematics, physics,
and Greek in Brünn (now in the Czech Republic). In his later years, he became the abbot (friar) of
his monastery and put aside his scientific work.
While Mendel's research was with plants, the basic underlying principles of heredity that he
discovered also apply to people and other animals because the mechanisms of heredity are
essentially the same for all complex life forms.
Through the selective cross-breeding of common pea plants over many generations, Mendel
discovered that certain traits show up in offspring without any blending of parent characteristics.

For instance, the pea flowers are either purple or white--intermediate colors do not appear in
the offspring of cross-pollinated pea plants.

Mendel observed __________ traits (specific characteristics)that are easily recognized and
apparently only occur in one of two forms:
o flower color is __________________________________
o flower position is ________________________________
o stem length is _______________________________
o seed shape is ___________________________________
o seed color is ________________________________
o pod shape is ____________________________________
o pod color is _________________________________

The pea plant was favorable organism for
these studies because it was self-fertilizing

When he made crosses, he followed only 1 or
2 (out of his 7) ____________ (characters) at
a time

He employed a very consistent method:
-
Opened flower & placed pollen from
one type onto the stigma

Mendel _______________ each flower with
little bag

When pods were ripe harvested them and
planted ________________

He _____________ the number of each type
of offspring and carefully recorded all of his data.
Mendel’s 1st and 2nd Experiments:

Crossed (P1):

(P1) =

Pure (true) breeding

Predictions: The offspring would be:





All tall
All short
All intermediate
Some would be tall and some short
1st Exp (P1): Crossed:
o

All offspring (F1):
o These offspring of the parental generation are
called _________________, which are offspring with different traits than parents.
o (F1) =

2nd Exp: Bred F1
o Results: Ratio of 787 tall to 277 short ________

Mendel assumed that the two “_______________” for each trait must exist in the parental
germ cells producing the gametes (pollen / egg)

These “factors” are called _________________

Each allele came from the parents and were united in ____________________.

In forming pollen and egg, the two alleles for any trait must separate and go into different
__________________

This became known as Mendel’s “____________________________________”
Mendel’s 3rd Experiment:

Crossed one of the F1 tall plants with its dwarf parent:
o

Possible Outcomes:
o All would be tall
o Mixture of Tall & Dwarf
o All would be intermediate

After the third experiment, Mendel formulated his
“Principles of Dominance” which states:

Used capital letter to denote what he called the
_______________ form of the trait: T = ______

Used lower case letter to denote what he called the
______________ trait: t = _______________________

Thus for the Tall and Dwarf crosses:
o TT =
o tt =
o Tt =

Pure-breeding forms later called _________________________

Hybrids later called __________________________
Test Cross:

Mendel recognized that it is not always possible to tell what offspring will be like by
inspecting the parent

Mendel could test if tall plants were pure-breeds (homozygotes) or hybrid (heterozygotes) by
the __________________ or _____________________

What % would you predict for each genotype (genetic
make-up)?
Punnett Squares:

It was now possible to account for the 3:1 ratio in the
F1 in Mendel’s second experiment:

This method of calculating traits of offspring in each
generation is called a ________________________.

The ___________________________ that might result
from a genetic cross can be determined by drawing a
Punnett square.

Punnett squares help to determine ________________ and __________________

Phenotype –

Genotype –
Independent Assortment:

After showing alleles ___________________ during the formation of
_________________, Mendel wondered if they did so independently.

In other words,

Example: Does the gene for seed color have anything to do with the
gene for seed shape?

To answer these questions, Mendel performed an experiment to
follow two different genes as they passed from one generation to the
next.

This experiment is known as the _____________________ or
__________________________

Mendel chose two different characteristics of the pea:
- Seed Coat:
- Seed color:

First, Mendel crossed pure-breeding plants that produced only round yellow peas (________)
with plants that produced wrinkled green peas (________).

All of the F1 offspring produced _______________________ (__________).

This proved round and yellow must be _________________alleles.

Try doing the Punnett square.

This cross does not indicate whether _____________________________________.

This cross only provided hybrids plants (F1) needed to produce an F2 generation that would
provide the answers to Mendel's question.

Mendel knew the F1 had a genotype of __________(___________________).

How would the alleles segregate into the F2

After Mendel counted the offspring of the dihybrid cross, he could make the following
conclusion.

__________ for different traits segregate _______________________ during the formation of
_______________.

This became known as Mendel’s second principle: __________________________
Summary of Mendel’s Principles:

1.
2.
3.
4.
Mendel’s principles form the basis of the modern science of genetics. These principles can be
summarized as follows: