Gregor Mendel Give peas a chance How a

Gregor Mendel “Give peas a chance!” How a monk learned about inheritance using a tasty vegetable

Gregor Mendel n n Gregor Mendel was a monk who loved gardening. In fact, he loved plants so much that he spent most of his adult life studying how certain traits were passed from “parent” plant to “baby” plant.

Mendel and his peas n Gregor Mendel is most famous for his scientific study of pea plants.

Pea plants have seven observable characteristics. Each characteristic has two possible traits. n n n n Characteristic Possible Traits 1. Plant height ---------------Long or short stems 2. Flower position along stem-------Axial or terminal 3. Pod color------------------Green or yellow 4. Pod appearance------------Inflated or constricted 5. Seed texture---------------Smooth or wrinkled 6. Seed color-----------------Yellow or green 7. Flower Color----------------Purple or white

Purebred By controlling plant pollination (fertilization), Mendel was able to create pea plants that were purebred for each trait. n This is also known as true breeding. n True breeding parent plants always produce offspring with the same trait. n

Purebred n Examples of Pure Breeding: n n n A purebred Labrador bred with a purebred Labrador will always produce fully Labrador offspring. A plant purebred for purple flowers will always produce offspring with purple flowers. A plant purebred for white flowers will always produce offspring with white flowers.

What happens if you cross two purebred plants? purple flowers x white flowers or wrinkled seeds x smooth seeds or tall plants x short plants etc,

Let’s take a look at flower color…. n Mendel called the purebred parents the P generation. n For each cross (plant “couple”), the P generation consisted of a purebred purple flower plant and a purebred white flower plant

Flower color cross n n n Mendel called the offspring plants the F 1 generation (1 for 1 st , F for filial- son or daughter) Plants in the F 1 generation are called hybrids because their parents have different traits. Mendel discovered that when he crossed a purebred purple flower plant and a purebred white flower plant, ALL of the offspring had purple flowers!

Crossing two purebred plants n n In every case of crossing two purebred plants, one trait “won out” in the F 1 generation. Examples: n n n Purple flower color “won out” over white flower colors Smooth seed texture “won out” over wrinkled seed texture. Why do you think this is? ? ?

Dominant and Recessive n n n Traits can be dominant or recessive! Mendel called the trait that appeared in the F 1 generation (purple flowers in this case) the dominant trait. Mendel called the trait that did not appear in the F 1 generation (white flowers) recessive trait.

What do you think happened when Mendel let plants from the F 1 generation self-pollinate? Did he end up with purebred purple flowers?

No!!!

Dominant and Recessive Traits n About 25% of the flowers in the F 2 generation were white! Even though the F 1 generation looked like purebred purple plants, they carried the trait for white flowers somewhere inside. n Where was this white flower trait “hidden”? ? n

The traits are hidden in the genes! n A gene is a segment of DNA that codes for a particular protein. The protein results in the trait. So…. . Each characteristic = One gene n For example: n n n There’s a gene for plant height There’s a gene for seed color There’s a gene for flower color etc. . .

Alleles n n Each alternative (different) form of a gene is called an allele. Examples: n n n The plant height gene has two alleles, tall and short. The flower color gene has two alleles, purple and white The seed texture gene has two alleles, wrinkled and smooth.

The gene is like the “address. ” The allele is like what or who you would find at the address.

From his research, Mendel came to two conclusions: n n 1. The Law of Segregation: Two factors (alleles) control each specific characteristic (gene). These factors (alleles) are separated during the formation of gametes. 2. The Law of Independent Assortment: Factors (alleles) for different characteristics (genes) are distributed to gametes independently. This means that the allele for seed texture isn’t dependent on the allele for plant height, etc.

As humans, our alleles are what create the diversity among us!