Introduction to Genetics

Ch 9

The Work of Gregor Mendel A. The branch of biology that studies heredity is

called genetics. B. Gregor Mendel is considered the father of

genetics who studied in a monastery. C. He planted hundreds of pea plants to study

their traits. D. He self-pollinated plants: 1. He brushed the pollen of one plant onto

itself

2. These parents inherited all the characteristics of the single plant that bore them.

E. He also cross pollinated plants. 1. He brushed the pollen of one plant

onto another.

2. He discovered that purebred tall

plants would only produce tall offspring. F. He studied many traits. 1. Other characteristics of the pea

plants are:

Round peas or Wrinkled Yellow peas or Green Gray peas or White Smooth pods or Constricted Green pods or Yellow Axial or Terminal Tall or Short

I. Dominance vs. recessive traits: 1. Dominant traits show through with one

parent’s dominant trait: Ex. Tt = Tall 2. This is known as a hybrid or heterozygous

(two different traits) T= Dominant for tallness t= Recessive for shortness 3. An organism will always show the

dominant trait.

4. Recessive traits show through only when an organism has two recessive traits.

5. Ex. tt = short 6. TT or tt are considered purebred or

homozygous because both genes from the mother and the father are the same.

7. Phenotype: The physical appearance of the offspring in a punnett square.

8. Genotype: The genetic makeup of the offspring.

J. Mendel’s experiment: F1 generation (segregation)

He crossed a purebred for tallness with a purebred for shortness:

TT x tt

The F2 generation would be Tt xTt

Do the following cross: Cross a hybrid for tallness with a purebred

for shortness: Tt x tt

Do the following cross: Two parents are hybrid for brown hair.

What are the probabilities of their offspring having brown or blond hair?