Genetics & Gregor Mendel Notes

© Fall 2005, Pflugerville ISD, 7th Grade

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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 found that the plants' offspring retained traits of the parents – this is now called “heredity”

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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.htm

p173 Life Science Textbook


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


Yes, copy the picture too.

• 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)


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

)


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, and was not expressed physically.

• 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 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.


Vocabulary

Heredity- the passing of traits from parent to offspring.Homozygous – both alleles are identical. Also known as True-breeding. Ex: PP or ppHeterozygous - 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 parentsSecond-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.


VocabularyRecessive trait- a trait that is apparent only when two recessive alleles for the same characteristic are inheritedGenes- a segment of DNA that carries hereditary instructions and is passed from parent to offspringAlleles- 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: White flowering plant crossed with red flowering plant produces a pink flowering plant.


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. X-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)

Wh

ite

Rab

bit

(b

b)


Google’s tribute to Mendel July 2011


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Genetics & Gregor Mendel Notes