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Gregor Gregor MendelMendel

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

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

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

Particulate InheritanceParticulate Inheritance

Why peas, Why peas, Pisum sativumPisum 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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Mendel and His PeasMendel 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

Mendel and His PeasMendel 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

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)

Mendel and His PeasMendel 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)

Mendel and His PeasMendel 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.

Mendel and His Peas

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

Mendel and His PeasMendel 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.

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?

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)

Google’s tribute to Mendel July 2011

What Did Mendel Find?He discovered different laws and rules that explain factors affecting heredity.

Rule of Unit FactorsEach organism has two alleles for each trait

Alleles - different forms of the same gene

Genes - located on chromosomes, they control how an organism develops

Rule of DominanceThe trait that is visible in the offspring is the dominant trait (uppercase)

The trait that disappears in the offspring is the recessive trait (lowercase)

Law of SegregationThe two alleles for a trait must separate when gametes are formed

A parent randomly passes only one allele for each trait to each offspring

Law of Independent Assortment

The genes for different traits are inherited independently of each other.

Mendel and His PeasVocabulary

1. 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.

Mendel and His Peas3. 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

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

Mendel and His Peas

9. Genotype- an organisms inherited combination of alleles

10. Phenotype- an organisms inherited appearance