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© Fall 2005, Pflugerville ISD, 7th Grade
copyright cmassengale
1
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
copyright cmassengale
© Fall 2005, Pflugerville ISD, 7th Grade
copyright cmassengale
4
Mendel stated that physical traits are inherited as “particles”Mendel did not know that the “particles” were actually Chromosomes & DNA
Particulate Inheritance
© Fall 2005, Pflugerville ISD, 7th Grade5
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
copyright cmassengale
© 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 allele. • 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 allele.
© 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. Trait- Each different form of a
characteristic such as stem height or seed color.
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
3. Genetics- The science of heredity.4. Fertilization- A new organism begins to
form when egg and sperm join together.
5. Purebred- An organism that is the offspring of many generations that have the same trait.
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas7. Genes- a segment of DNA that carries
hereditary instructions and is passed from parent to offspring; the factors that control a trait.
8. Alleles- multiple forms of the same gene.
9. Dominant Allele- one whose trait always shows up in the organism when the allele is present.
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
10. Recessive Allele- A trait that is hidden whenever the dominant allele is present.
11. Hybrid- An organism that has two different alleles for a trait.
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