Learning Goal 1The Work of Gregor Mendel

Background on Gregor Mendel

Details -

Reasons for Choosing Peas -

Mendel’s Experimental Design

His Pea Experiment -

Mendel’s Results -

Mendel’s Laws

Law of Dominance -

Law of Segregation -

Law of Independent Assortment -

Genetic Terms

Alleles -

Homozygous -

Heterozygous -

Genotype -

Phenotype -

Unit IV

Learning Goal 1Describe the research of Gregor

Mendel and predict the outcome of genetic crosses.

Background on Gregor Mendel

• Details• Austrian monk with an

interest in gardening and a good knowledge of mathematics.

• In the 1840’s he experimented with the traits of garden peas (Pisum sativum).

Reasons for Choosing the Garden Pea

• Many varieties exist.• Easy to observe

contrasting traits.• They self-pollinate.• They reproduce

quickly.

Mendel’s Experimental Design

• His Pea Experiment• He allowed each variety to self-

pollinate for several generations to ensure that they were true-breeding (offspring always exhibited the same trait). He called this the P1 (parent) Generation.

• He took two of these parent plants with contrasting forms of the same trait and cross-pollinated them.

• The plants that resulted from this cross were called the F1 Generation.

• Mendel then allowed the F1 plants to self-pollinate to produce the F2 Generation.

Mendel’s Results

• For every trait, one form would disappear from the F1 generation.

• The disappearing trait reappeared in the ¼ of the F2 generation.

• This was true of all seven traits that Mendel looked at.

• He used the term dominant to refer to the form of the trait exhibited in the F1 generation and recessive to refer to the disappearing trait.

Mendel’s Laws

• Law of Dominance –

One form of each trait is dominant and one is recessive.

Law of Segregation

• Members of each gene pair (alleles) separate during gamete formation (meiosis).

Law of Independent Assortment

• The genes for different traits separate independently from one another during gamete formation.

Genetic Terms

• Alleles – members of a gene pair symbolized by letters. Dominant alleles are capital letters, and recessive alleles are lower case.

• Homozygous – the alleles of a gene pair are identical (RR or rr).

• Heterozygous – the alleles of a gene pair are different (Rr).

• Genotype – describes the types of alleles of a gene pair

• Phenotype – describes the expression of the trait in the appearance.