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

Gregor Mendel Born in 1822. Gregor Mendel was a monk who taught high school and worked in the monastery gardens. 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.

Gregor Mendel Genetics: the scientific study of heredity. Considered the “Father of Genetics” due to his work studying inheritance. Genetics: the scientific study of heredity.

Mendel and his peas Gregor Mendel is most famous for his scientific study of pea plants. He chose pea plants because they reproduce quickly and produce large amounts of offspring.

Pea plants have seven observable characteristics Pea plants have seven observable characteristics. Each characteristic has two possible traits. 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. This is also known as true breeding. When they self-fertilize, true breeding parent plants always produce offspring with the same trait.

Purebred Examples of True Breeding: A purebred Labrador bred with a purebred Labrador will always produce fully Labrador offspring. No Chihuahuas??? A self-pollinating plant purebred for purple flowers will always produce offspring with purple flowers. A self-pollinating 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 tall plants x short plants Labrador x Poodle

Let’s take a look at flower color…. Mendel called the purebred parents the P generation. For each cross (plant “parents”), Mendel cross-pollinated plants who were true breeding with opposite traits. Example: the P generation consisted of a purebred purple flower plant and a purebred white flower plant

Flower color cross Mendel called the offspring plants the F1 generation (1 for 1st , F for filial- son or daughter) Plants in the F1 generation are called hybrids because their parents have different traits. What do you think Mendel expected to see when he crossed a purebred purple flower plant with a purebred white flower plant?

All of the hybrid, or F1 Generation, offspring had purple flowers!

Crossing two purebred plants In every case of crossing two purebred plants, one trait “won out” in the F1 generation. Examples: 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 Traits can be dominant or recessive! Mendel called the trait that appeared in the F1 generation (purple flowers in this case) the dominant trait. Mendel called the trait that did not appear in the F1 generation (white flowers) recessive trait.

Did he end up with purebred purple flowers? What do you think happened when Mendel let plants from the F1 generation self-pollinate? Did he end up with purebred purple flowers?

No!!!

Dominant and Recessive Traits About 25% of the flowers in the F2 generation were white! Even though the F1 generation looked like purebred purple plants, they carried the trait for white flowers somewhere inside. Where was this white flower trait “hidden”??

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

Alleles Each alternative (different) form of a gene is called an allele. Examples: 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.

In other words… Inheritance is determined by factors (genes) that are passed from one generation to the next. These genes can come in different forms called alleles. Law of Dominance: Some alleles are dominant and others are recessive

For every gene, how many alleles do you get from each parent? This is a result of what process??

From his research, Mendel came to two conclusions: 1. The Law of Segregation: Two factors (alleles) control each specific characteristic (gene). These factors (alleles) are separated during the formation of gametes (meiosis). 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!

Terminology Alleles are represented with letters Dominant – The allele/trait that is expressed (T) Recessive – The allele/trait that is hidden (t) Genotype – The allele makeup of a gene (TT, Tt, tt) Phenotype – The physical appearance of a trait (Tall plant, purple flowers, etc)

Genotypes and Phenotypes There are three possible genotypes: Homozygous Dominant (BB, TT, PP) Homozygous Recessive (bb, tt, pp) Heterozygous (Bb, Tt, Pp) Homozygous: Has two of the same allele. Heterozygous: Has one of each allele.

Mendelian Genetics

Punnett Squares Mendel’s work has allowed us to be able to predict possible offspring outcomes between two known genotypes. This prediction is illustrated through a punnett square.

Monohybrid Crosses Two heterozygous tall plants are allowed to cross-pollinate. Use a punnett square to predict the genotype and phenotype probabilities.

Monohybrid Crosses Genotype Probabilities: Phenotype Probabilities: TT: 25% Tt: 50% Tt: 25% Phenotype Probabilities: Tall: 75% Short: 25%