MENDEL used PEA PLANTS to find the rules of

GENETICS

Why? Do you know the shape of pea flowers?

Why? Do you know the shape of pea flowers?

Pollen matures in anthers.

When pollen comes into contact with the stigma, the ovules

in the ovary are fertilized

and form the seeds, then ovary becomes

the pod.Ovules in

The shape of a pea flower is very important : petals cover the stigma from pollen of other flowers, thus promoting self-pollination

Now, in these pea flowers, do you see the anthers with pollen and do you see the stigma???

No, of course, because petals close pollen and anthers into the flower.

That is why Mendel decided to use peas to understand genetic rules: it is sure that pollen, with the father information, drops only on the ovules with the mother information of the same flower (You know that often pollen is transported by wind or by insects but this in not possible in the pea flowers because the pollen is hidden into the flower).

The seven characters

Mendel’s genetics

Moreover pea plants are easy to grow and are not expensive.So Mendel thought they were an optimum material to study how characters can be transmitted from parents to next generations.

Before starting the study of the characters’ transmission,

Mendel started to study a lot of different pea plants:

he found 22 different pea plants

and for two years he studied these plants, how they grew, how the children were, to find traits (characters) that were very easy to recognize.

SEVEN were the characters that he found

These are the seven characters that Mendel studied:

PURE LINESPURE LINES

Then Mendel decided to be sure that

So for many generations he planted

• At the end he called these plants

An example: the pure line of a red flower

• Individuals that belong to pure line have the same characters from one generation to another

START!!!!Mendel could start: he had all that he needed for his experiments because he had:

- 7 different characteristics to analyze

- pure lines for each characteristic

CROSS-POLLINATION ….

So Mendel kept the pollen of a pure line red flower and put it on a stigma of pure line white flower: we call this cross pollination

Parental generation ＝

P

QUIZ: what did he obtain? Red flowers or white flowers or some red and some white flowers???

QUIZ: what did he obtain? Red flowers or white flowers or some red and some white flowers???

Mendel chose to artificially breed pure lines of plants such as red flowers and white flowers.

He obtained only

red flowers!!!!

Parental generation ＝

P

1st generation of children ＝

F1

XParental generation ＝ P

1st generation of children ＝ F1

X

Why does a character always disappear? Where has the information for white (flower), green (seed), or terminal (position of flower) gone ?

Why does a character always disappear? Where has the information for white (flower), green (seed), or terminal (position of flower) gone ?

Experiments with pure lines of green and yellow peas,

axial or terminal flowers These are the results:

Parental generation ＝ P

1st generation of children ＝ F1

Hoping to understand more about this problem, Mendel decided to analyze another generation: the 2nd filial generation (F2).To obtain the F2 Mendel carried out a self pollination: he didn’t touch flowers of F1 so the pollen went on the stigma of the same flower.

Mendel let F1 generation plants self-pollinate and obtained the following generation (F2).

F1

…AND SELF POLLINATION

P

F1

F2

The missing characters in the F1 generation (white) reappeared in the following generation (F2)!!!.

The white (flower) character reappeared!

pollen

pollen

polle

n

polle

n

pollen

CROSS-POLLINATION

SELF-POLLINATION

P

F1

F2

QUIZ: how much information 1s present in the F1 about the colour of flowers?QUIZ: how much information is present in each flower about its colour ?

QUIZ: how much information 1s present in the F1 about the colour of flowers?QUIZ: how much information is present in each flower about its colour ?

Mendel called DOMINANT the character that appeared in the F1 generation (red flower) and RECESSIVE the character (white) that was present but not expressed.

Mendel thought that the information white was present also in the F1 but was hidden.So in the F1 is present the white information but obviously is present also the red information!!!

Mendel thought that the information white was present also in the F1 but was hidden.So in the F1 is present the white information but obviously is present also the red information!!!

red information+white information=red colour

P

F1

F2

So it is So it is

reasonable to reasonable to

say that the say that the

colour of pea colour of pea

flowers is flowers is

always always

controlled by controlled by

two factorstwo factors: :

red (dominant) red (dominant)

and and

white white

(recessive). (recessive).

So it is So it is

reasonable to reasonable to

say that the say that the

colour of pea colour of pea

flowers is flowers is

always always

controlled by controlled by

two factorstwo factors: :

red (dominant) red (dominant)

and and

white white

(recessive). (recessive).

Also the pure lines have two factors but of the same type.

white inf.+white inf.=white colour

red inf.+red inf.=red colour

red information+white information=red colour

pure lines

red information+white information=red colour

Only one item of information for the colour of the flower (red or white) is present in the pollen and in the ovule (one in the pollen, one in the ovule).Since the new flower has two parents, it receives 2 items of information (one from the pollen, one from the ovule).

The meiosis separates the two items of information so in the gamets (pollen and ovule) the information is again one.

P

F1

P

F1

F2

The pure lines have only one kind of factor .

…and the F2 generation? Also the flowers of the F2 has two factors (=alleles) received by its parents (the F1 flowers,obviously!)The colour of pea flower is controlled by two alleles: red ( dominant) and white (recessive)

The F1 is only red because all flowers have one red (dominant) information.

In F2 the white colour reappears because some flowers have the two items of information for the white colour.

Mendel carried out similar experiments with all characters (do you remember the 7 characters that he found?) and always one character disappeared in the F1 but reappeared in F2.

XP

F1

F2

Cross-pollination of pure lines

Self-pollination

Every 3 dominant characters there is 1 recessive character

(3:1)

If one allele (factor, unit) is dominant, the character will be dominant, if no allele is dominant, character will appears recessive.

The allele is designed with a capital letter if dominant, small letter if recessive.

CONCLUSIONEvery character is given by two alleles (factors, units): mother transmits 1 allele to every child and so father does .

Red

So each child receives 2 alleles. Conventionally the allele is designed by a letter.

• Mendel cross-pollinated two pure plants, one with red flowers and one with white flowers and called they PARENT GENERATION. From this cross he obtained a FIRST GENERATION (F1), in which all the plants showed only red flowers, while the character of the white flower seemed to have disappeared. Mendel called the character that appeared in the F1 generation DOMINANT (red flower).

• He then let F1 generation plants self-pollinate and saw that the missing character in the F1 generation (white) reappeared in the following generation (F2). This character was called RECESSIVE. In the F2 generation the dominant and recessive characters were in a ratio of 3:1.

• a) The inheritance of each character is determined by units or factors that are passed unchanged to the descendents;

• b) Each individual inherits one unit from each parent for each character;

• c) The character may not appear in an individual but can still be passed to the next generation.

• Alleles are alternative forms of the same gene which has a defined character.

• There are individuals:

• HOMOZYGOUS, having two identical alleles. In this case they can be dominants if they have both dominant alleles or recessives if both alleles are recessive

• HETEROZYGOUS, who have inherited different alleles from each parent.

Let us summarize…and formalize