Gregor Mendel

Chapter 11

Gregor Mendel’s Life (1822-1884)

Born in Austria (now Czechoslovakia) in 1822Only son of a peasant farmer.Entered the monastery in 1843 to avoid a life of poverty.Ordained a priest in 1847.Monastery a center for teaching and scientific research. Taught math, physics, and GreekStudied at the University of Vienna. Did not do well.

Returned to monastery in 1853; considered a failure.Interested in selective breeding for favorable traits.Choose to work with peas. (Pisum sativum) First to collect mathematical data.His published work was ignored by other scientists.In 1868, elected Abbot of his Monastery.

His work stored at the monastery was burned after his death in 1884.

Forgotten until his work was rediscovered in 1900.

Today he is known as the Father of Genetics

Gregor Mendel carried out the first important studies of heredity, the passing on of characteristics from parent to offspring.Characteristics that are inherited are called traits. Predicted how traits are

transferred from one generation to the next. First scientist to record data and

use mathematical calculations.

Pea Plants

Garden peas reproduce sexually.Have male (pollen) and female (egg or ovule) gametes.Pollination is the transfer of pollen to the female organ.Fertilization occurs when the pollen and egg fuse together.The fertilized ovule matures into a seed.

Making a cross

Mendel transferred pollen from one plant to another plant with different traits.

Monohybrid Cross

Bred tall plants to be tall for many generations – called pure.

Bred short plants to be short for many generations – called pure.

Crossed pure tall and pure short. 100% of offspring were tall.

Parent generation

F1 generation

Mendel crossed two of the F1 generation. ¾ of offspring were

tall. ¼ offspring were

short.

This generation called the F2.Mendel did this same experiment with 7 other traits.

Mendel concluded that each organism has two factors for each of its traits. We now call these

factors genes. Alternative forms of

genes are called alleles. Alleles are located on the

chromosomes – one from mother and one from father.

Dominant and Recessive

Traits are dominant or recessive.

When an organism has two different alleles, the one that is observed is called dominant.

The trait that is hidden is called recessive.

Recessive is only seen if both alleles are recessive.

The Law of Segregation

The two alleles for each trait must separate when the gametes are formed.

A parent passes on only one of its two alleles to the offspring.

Capital letter = Dominant alleleSmall letter = Recessive allele

Two organisms can look alike but have different alleles. (TT or Tt)

The way an organism looks is called its phenotype.

The actual genes (alleles) an organism has is called its genotype.

Homo or Hetero

An organism is homozygous if both alleles are the same. TT = homozygous dominant tt = homozygous recessive.

An organism is heterozygous if the alleles are different. Tt = heterozygous or hybrid.

Punnett Square

In 1905, Reginald Punnett created a short-hand way to determine the expected proportions of possible genotypes.

Called a Punnett Square

The capital letter, or dominant trait, should be written before the lower case, recessive trait.

Law of Independent Assortment

Genes for different traits are inherited independently of each other.

That means that traits like height and seed color are not linked together.

Dihybrid Cross

A cross involving two traits is called a dihybrid cross.

The traits are independently assorted.

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