mendel notes

© Fall 2005, Pflugerville ISD, 7th Grade

copyright cmassengale

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Gregor Mendel

(1822-1884)The Father of Genetics


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

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Gregor Johann Mendel

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

He discovered how heredity works – how organisms transfer their traits to their offspring.

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copyright cmassengale

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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


Why peas, Pisum sativum?

Why Peas?Produce lots of offspring Grow quicklyCan be grown in a small area Can be artificially cross-pollinated

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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.htmp173 Life Science Textbook


Mendel and His Peas

• 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


Yes, copy the picture.

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

• Where did the white color go??

(Pp)

(Pp)

(Pp) (Pp)

Purple Parent (PP)

Whi

te P

aren

t

(pp)


• Mendel crossed his first generation (F1 x F1) purple flowered plants together.

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

(PP) (Pp)

(Pp) (pp)

Purple Parent (Pp)

Purp

le P

aren

t (Pp

)

Yes, copy the picture.


Below is a pedigree of two peas and their offspring.


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 away, and was not

expressed physically.• But - it showed up in the next

generation!


Mendel and His Peas

• The purple that overpowered the recessive color was named the dominant trait.


Mendel and His Peas

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

• These sets of instructions are called alleles. (remember the “Genetics Notes?”)


Vocabulary

- Heredity- the passing of traits from parent to offspring.- Homozygous – both alleles are identical. Also known as True-breeding. Ex: PP or pp- Heterozygous - each allele is different. Also known as hybrids. Ex: Pp


Vocabulary

- P generation- the parent generation.- First-generation or F1- the very first set of

offspring from two parents- Second-generation or F2 – the offspring of

the kids from the F1 generation (grandkids)- Dominant trait- Represented with a capital letter, it overpowers the recessive trait.


Vocabulary-Recessive trait- a trait that shows up only when two recessive alleles for the same characteristic are inherited-Genes- a section of DNA that carries hereditary instructions and is passed from parent to offspring-Alleles- multiple forms of the same gene


VocabularyGenotype- the genetic code. Ex: PpPhenotype- the physical appearance. Ex: Purple FlowersPedigree – your family tree.Incomplete Dominance – a blend of the parents’ phenotypes.

Ex: Bb light brownbrown white


VocabularyCodominance – When both phenotypes are visible. Ex: Hair that has both blond strands and brown strands. Karyotype – a chart of all your chromosomes lined up in order.Sex Chromosomes – chromosomes that determine a person’s gender. ex: XX and XYX-linked, or sex-linked inheritance – see p186 in Life Science Book.


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)

Whi

te R

abbi

t (bb

)


Google’s tribute to Mendel July 2011


Science Humor

mendel notes

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