The Origin of Modern Genetics 6A

Objectives I will be able to describe Mendel’s experiments with the genetics of peas. I will be able to summarize the theories Mendel developed to explain the results of his experiments. I will be able to differentiate between purebred and hybrid. I will be able to explain the difference between dominant and recessive alleles.

Gregor Mendel the father of genetics

(the study of inheritance) Genetics the study of how traits are passed from parents to offspring (the study of inheritance)

the passing of traits from parents to offspring Heredity the passing of traits from parents to offspring Trait: a genetically determined characteristic or condition

Gregor Mendel Mendel's work was done about 140 yrs. ago, but even now much of what we know about genetics is based on Mendel's work and illustrated by it.

Gregor Mendel was born in 1822 on a farm in Heinzendorf, Austria At age 21 entered the Augustinian order of the Roman Catholic Church As a monk he - studied science at the University of Vienna and became an excellent mathematician

Gregor Mendel As a school teacher - he engaged in many scientific activities At a monastery - he began a program of selective breeding of peas. After 8 yrs. of raising 30,000 pea plants and recording and classifying many pages of notes, he wrote a paper with his conclusions called Mendelian Genetics (1865).

Mendel’s Experimental Methods Mendel studied genetics by doing controlled breeding experiments with pea plants. There are two types of pollination: self-pollination cross-pollination

Self-Pollenation

Mendel’s Experimental Methods When a true-breeding (purebred/homozygous) plant self-pollinates, it always produces offspring with traits that match the parent. Mendel cross- pollinated pea plants himself and recorded the traits that appeared.

Cross-Pollenation

Mendel’s Results Once Mendel had enough true-breeding plants for a trait he wanted to test, he cross-pollinated selected plants. Plants are called hybrids if they come from true-breeding parent plants with different forms of the same trait.

First-Generation Crosses

Mendel’s Results hybrid Science Use the offspring of two animals or plants with different forms of the same trait Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor

Mendel’s Results Mendel also cross-pollinated hybrid plants. He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.

Second-Generation (hybrid) Crosses

Mendel’s Results Mendel recorded traits of offspring from many hybrid crosses.

Mendelian Genetics His paper was the first recorded study of how traits pass from one generation to the next. Mendel also was the first to use the mathematics of probability to explain heredity.

Mendelian Genetics When Mendel's paper was published, in 1865, it received little attention, and was rarely cited by botanists or biologists during the next 34 years. In 1900, Mendel's work was cited by three botanists, writing in different parts of Europe: Hugo de Vries, in Amsterdam; Carl Correns, in Tübingen; and Eric Von Tcshermak, in Esslingen, Austria.

Mendel's Theories the concept of unit characteristics the concept of dominant and recessive the concept of segregation

the concept of unit characteristics Mendel concluded that two factors, one from the sperm and one from the ovum, control each inherited trait. if factors were the same - purebred TT (tall) tt (short) if factors were not the same - hybrid Tt (tall)

Purebred / Homozygous If an organism’s two alleles for a trait are the same, the organism is purebred for that trait.

Hybrid/ Heterozygous If an organism’s two alleles for a trait are different, the organism is hybrid for that trait.

The Concept of Dominant and Recessive Dominant trait - a genetic factor that blocks another genetic factor. Recessive trait - a genetic factor that is blocked by the presence of a dominant factor. The dominant allele (factor) completely masks the presence of the recessive allele (factor).

the concept of segregation Mendel reasoned that when a cell forms gametes, the genes separate (segregate) so that there is only 1 gene for each characteristic in each gamete.

Principles of Heredity Traits are controlled by alleles on chromosomes. An allele’s effect is dominant or recessive. When a pair of chromosomes separates during meiosis the different alleles for a trait move into separate sex cells.

Mendel's peas genetics - Experiments that changed the world.