© Fall 2005, Pflugerville ISD, 7th Grade

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Gregor Gregor MendelMendel

(1822-1884)(1822-1884)The Father The Father of Geneticsof Genetics

© Fall 2005, Pflugerville ISD, 7th Grade

Gregor Johann MendelGregor Johann MendelAustrian monkAustrian monkStudied the Studied the inheritanceinheritance of traits in of traits in pea plantspea plantsDeveloped the Developed the laws of laws of inheritanceinheritanceMendel's work was Mendel's work was not recognized until not recognized until the turn of thethe turn of the 20th 20th centurycentury

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© Fall 2005, Pflugerville ISD, 7th Grade

Gregor Johann MendelGregor Johann Mendel

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

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

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© Fall 2005, Pflugerville ISD, 7th Grade

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

Particulate InheritanceParticulate Inheritance

© Fall 2005, Pflugerville ISD, 7th Grade

Why peas, Why peas, Pisum sativumPisum sativum??

Can be grown in a Can be grown in a small areasmall area Produce Produce lots of lots of offspring offspring Produce Produce purepure plants plants when allowed to when allowed to self-self-pollinatepollinate several several generations generations Can be Can be artificially artificially cross-pollinatedcross-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)

© 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)

© 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)

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Google’s tribute to Mendel July 2011

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Science Humor

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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

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Mendel and His Peas

9. Genotype- an organisms inherited combination of alleles

10. Phenotype- an organisms inherited appearance