Gregor Mendel1822-1884Father of Genetics: Principles of biological and hereditary traits

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

Gregor J. Mendel

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

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

Vocab To Keep in mind

• Heredity- the passing of traits from parent to offspring.• 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.

• Dominant trait- the trait observed when at least one dominant allele for a characteristic is inherited

• Recessive trait- a trait that is apparent only when two recessive alleles for the same characteristic are inherited

• Genes- a segment of DNA that carries hereditary instructions and is passed from parent to offspring

• Alleles- multiple forms of the same gene• Genotype- an organisms inherited combination of alleles• Phenotype- an organisms inherited appearance

Inheritance

Mendel stated that physical traits are inherited as “particles”Mendel did not know that the “particles” were actually Chromosomes & DNAChromosome: a threadlike structure of nucleic

acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Gene: a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.

Why grow peas?

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

Mendel’s tests

• Mendel tested 7 traits:1. Flower color2. Flower position3. Seed color4. Seed shape5. Pod shape6. Pod color7. Plant height

The 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)

The Peas cont’d

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

• Where did the white color go??

  (Pp)

  

(Pp)

   (Pp.)    (Pp)

Purple Parent (Pp)

Purp

le P

aren

t (Pp

)

The Peas cont’d

• 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)

Purp

le P

aren

t (Pp

)

Purple Parent (Pp)

Mendel & The 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.

Mendel & The Peas

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

Traits

• 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”).

• Trait- a distinguishing quality or characteristic, typically one belonging to a person

Test your knowledge

• 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?

• Which trait is recessive?

And the answer is….

• The trait for black fur is dominant over the trait for white fur. The white fur trait is recessive.

  (Bb)

  (Bb)

 

(Bb)   (Bb)

Whi

te R

abbi

t (bb

)

Black Rabbit (BB)

Review

• Heredity- the passing of traits from parent to offspring.• 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.

• Dominant trait- the trait observed when at least one dominant allele for a characteristic is inherited

• Recessive trait- a trait that is apparent only when two recessive alleles for the same characteristic are inherited

• Genes- a segment of DNA that carries hereditary instructions and is passed from parent to offspring

• Alleles- multiple forms of the same gene• Genotype- an organisms inherited combination of

alleles• Phenotype- an organisms inherited appearance

Any last questions???