Mendel

© Fall 2005, Pflugerville ISD, 7th Grade

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Gregor Mendel

(1822-1884)The Father of Genetics

© Fall 2005, Pflugerville ISD, 7th Grade2

Gregor Johann Mendel

Austrian monkStudied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendel's work was not recognized until the turn of the 20th century

© Fall 2005, Pflugerville ISD, 7th Grade3

Gregor Johann Mendel

Between 1856 and 1863, Mendel cultivated and tested thousands of pea plants

He found that the plants' offspring retained traits of the parents

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© Fall 2005, Pflugerville ISD, 7th Grade

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Mendel stated that physical traits are inherited as “particles”Mendel did not know that the “particles” were actually Chromosomes & DNA

Particulate Inheritance

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Why peas, Pisum sativum?

Can be grown in a small area Produce lots of offspring Produce pure plants when allowed to self-pollinate several generations Can be artificially cross-pollinated

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© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

• Mendel tested 7 traits:1. Flower color2. Flower position3. Seed color4. Seed shape5. Pod shape6. Pod color7. Plant height

http://www.fieldmuseum.org/exhibits/traveling_mendel.htm

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

• Mendel crossed flowers that were true-breeding for each characteristic.

• He crossed a purple (PP) flowered plant with a white (pp) flowered plant. (Parent Generation)

http://biology.kenyon.edu/courses/biol114/KH_lecture_images/Mendel/Mendel.html

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

• The first generation (F1) of plants all had purple flowers.

• Where did the white color go??

  (Pp)

(Pp)

   (Pp)    (Pp)

Purple Parent (PP)

Wh

ite

Par

ent

(p

p)

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas• Mendel took two of his

first generation (F1 x F1) purple flowered plants and crossed them together.

• In the second generation (F2) he had 3 purple flowered plants, and 1 white flowered plant.

(PP)   (Pp)

  (Pp)   (pp)

Purple Parent (Pp)

Pu

rple

Par

ent

(Pp

)

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

• Mendel noticed in the first generation, all of the white flowers seemed to disappear.

• He called this a recessive trait. • The white color faded into the

background at first. • It showed up in the next generation

when he pollinated the flowers.

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

• The color (purple) that seemed to mask over the recessive color was named the dominant trait.

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

• Mendel was responsible for figuring out that each plant carried two sets of instructions for each characteristic (one from the “mom” and one from the “dad”).

• Like many scientists, his work was not accepted until after his death.

© Fall 2005, Pflugerville ISD, 7th Grade

Let’s Review

1. If you crossed a true-breeding black rabbit with a true-breeding white rabbit, all of the offspring would be black. Which trait is dominant in rabbits: black fur or white fur?

2. Which trait is recessive?

© Fall 2005, Pflugerville ISD, 7th Grade

Answer

• The trait for black fur is dominant over the trait for white fur. The white fur trait is recessive.

http://www.buckeyevalleyfarms.freeservers.com/photo.html

  (Bb)

  (Bb)

(Bb)   (Bb)

Black Rabbit (BB)

Wh

ite

Rab

bit

(b

b)

© Fall 2005, Pflugerville ISD, 7th Grade

Google’s tribute to Mendel July 2011

© Fall 2005, Pflugerville ISD, 7th Grade

Science Humor

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

Vocabulary1. Heredity- the passing of traits from

parent to offspring.2. Self-pollinate- A plant is often able to

pollinate by itself because it contains both the male and female reproductive structures. This only requires 1 parent.

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

3. True-breeding- all of the offspring will have the same trait as the parent when self-pollinated

4. First-generation- the very first set of offspring from two parents

5. Dominant trait- the trait observed when at least one dominant allele for a characteristic is inherited

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas6. Recessive trait- a trait that is apparent

only when two recessive alleles for the same characteristic are inherited

7. Genes- a segment of DNA that carries hereditary instructions and is passed from parent to offspring

8. Alleles- multiple forms of the same gene

© Fall 2005, Pflugerville ISD, 7th Grade

Mendel and His Peas

9. Genotype- an organisms inherited combination of alleles

10. Phenotype- an organisms inherited appearance