Mendel's Experiment

Theory of Inheritance

Gregor Mendel

Monk in a monastery in the Czech Republic.

First to scientifically study how traits are inherited.

Over 8 years, bred pea plants to follow inheritance. He chose pea plants because:

Observation

He observed:

stem length

pod shape

seed colour

seed shape

flower position

flower colour

pod colour

Monohybrid

Every experiment started with true breeding for a trait, but that exhibited a different form of the trait.

called the P (parental) generation.

Offspring called F1 (first filial) generation.

Experiments called monohybrid crosses because only one trait is monitored at a time.

Results

First filial generation of male yellow-pea-producing and female green-pea-producing, one parent seed colour trait seemed to disappear.

Second filial generation had 3:1 ratio yellow to green.

Law of Segregation

There are two hereditary factors. Today, they are called "alleles".

Pairs of homologous chromosomes carry the same genes, but may carry different forms of those genes ("alleles").

One allele is dominant, the other is recessive.

Traits are determined by pairs of alleles that segregate during meiosis.

Phenotype: physical description.

Genotype: combination of alleles for a characteristic.

Homozygous: same alleles.

Heterozygous: different alleles.

Dominant allele: represented by first letter of allele's description, and in upper case

Recessive allele: represented by first letter of allele's description, and in lower case