Introduction to Genetics

The Work of Gregor Mendel

Biology Text Chapter 11

The Beginning of Genetics

• Genetics is the study of heredity (Traits we inherit from our parents).

• Gregor Mendel was an Austrian Monk who was in charge of the monastery garden. Mendel carried out experiments with garden peas.

• The original pea plants Mendel had were true-breeding. True-breeding plants produce offspring identical to themselves. Tall seeds produced tall plants, some produced yellow seeds, etc.

Cross Pollination• To cross pollinate pea plants, Mendel

cut off the male parts of one flower, then using a brush dusted it was pollen of another flower.

• In the example to the left, a purple flower (Parent plant) was crossed with a white flower pea plant (Parent plant).

• Purple flower color is dominate over the white color. The first generation (F1)of plant expresses its color as purple, but also has recessive genes for white flowers that might be expressed in its offspring.

Genes and Dominance• Mendel studied seven different

pea plant traits.• Traits are specific

characteristics, like seed color or plant height that varies from one individual to another.

• Mendel crossed plants with the seven different traits.

• Each original plant is a parent (P) generation. The offspring are called F1 or first filial. Filial is Latin for son or daughter.

• Hybrids are the offspring of parents with different traits.

Mendel’s Conclusions

• Mendel’s first conclusion was that traits are passed from one generation to the next. From parents to offspring.

• Scientists call the chemicals that control and determine traits genes.

• Different forms of a gene are called alleles. Alleles for plant height are short or tall. Seed shape is a round allele or wrinkled allele, etc.

Principle of Dominance

• Mendel’s second conclusion is the principle of dominance

• The principle of dominance states that some alleles are dominant and others are recessive. When a dominant and recessive allele are on a gene, the dominant allele will express over the recessive gene.

• The capital letter represents the dominant allele and the lowercase letter represents the recessive allele

Segregation• Mendel wondered what happened to the

recessive alleles from the parent plant.• He crossed two of the hybrid F1 plants to

produce the F2 or second filial generation.

• The alleles separated during the formation of gametes (sex cells) in the F1.

• As the male and female gametes came together, different dominant and recessive plants were produced in the F2 generation.