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Gregor Mendel

Contribution in the

field of Genetics

DATE OF BIRTH

July 22, 1822

Mendelian GeneticsAugustinian Monk at Brno Monastery in Austria (now Czech Republic)

Not a great teacher but well trained in math, statistics, probability, physics, and interested in plants and heredity.

While assigned to teach, he was also assigned to tend the gardens and grow vegetables for the monks to eat.

Mountains with short, cool growing season meant pea (Pisum sativus) was an ideal crop plant.

• Gregor Mendel• “Father of Genetics”

MENDELIAN GENETICSThe science of modern genetics had its humble beginning in the garden of an Austrian monk in the 1860s.The monk was Gregor Mendel, and his contribution to the study of heredity is discussed in every biology textbook.Ironically, his work was ignored and not rediscovered until the beginning of the 20th century.

What did Mendel do??

He studied the characteristics of pea plants, and how they were passed from generation to generation.The seven characteristics that he observed can be seen in the illustration to the right. Fortunately these traits were carried on different pairs of chromosomes.By controlling the transfer of pollen, he was able to conduct cross-fertilization experiments.Did you know that although Mendel did his work in the 1860’s, it was ignored and not rediscovered until 1901?

*Monohybrid CrossA monohybrid cross looks at a single

characteristic. In this case Mendel examined flower color

Analysis lead to the following four hypothesisThese ideas are very important!• There are alternative forms of genes that account for

variations in inherited of characteristics. We call these alternative forms alleles.

• For each characteristic, an organism inherits two alleles, one from each parent. If the alleles are the same they are said to be homozygous. If the two alleles are different they are said to be heterozygous.

• If the two alleles of an inherited gene pair differ, then one determines the organism’s appearance and is called the dominant allele. The other has no effect and is called the recessive allele.

• A sperm or egg carries only one allele for each inherited trait because allele pairs separate from each other during meiosis and the production of gametes. This is the Law of Segregation.

Don’t know the genotypes? Use a

Testcross!

Cross the unknown genotype with an individual that

is homozygous recessive.

Contributions in 1860s (US Civil War Era)• Discovered Genes as Particles of Inheritance

• Discovered Patterns of Inheritance

• Discovered Genes Come from Both Parents Egg + Sperm = Zygote

Nature vs. Nurture

Sperm means Seed (Homunculus)

• Discovered One Form of Gene (Allele) Dominant to Another

• Discovered Recessive Allele Expressed in Absence of Dominant Allele

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All these leaves came from clones of the same plant grown under different light

conditions

Sex-linked Genes• In fruit flies and humans traits carried on the X chromosome

are said to be sex-linked. • A recessive gene on the X chromosome will always be

expressed in the male, since there is a single X present.• A female with the recessive gene on one of her two X

chromosomes will be able to pass the trait to her male offspring, but will not express the trait herself. She is a carrier.

• White eyes in Drosophila is one such sex-linked trait.

*Sex-Linked Disorders• Sex-linked disorders primarily

affect males since the defective gene is carried on the X chromosomes, and males have a single X chromosome.

• Females would have to be homozygous for a sex-linked condition for it to be expressed, however many females are heterozygous carriers for these recessive traits.

• Three well-known sex-linked disorders are:o Hemophiliao Duchene muscular dystrophyo Red-Green color blindness

Thank you