Download Slide 1 Gregor Mendel, presented by the Kaplan

Slide 1
Gregor Mendel, presented by the Kaplan University Science Center.
Slide 2
One of the major contributors to our understanding of inheritance and the science of genetics is Gregor
Mendel. He is also known as the father of genetics. Though he knew nothing about genes or
chromosomes, through a series of simple experiments using pea plants, he was able to discover some
basic laws of heredity and is credited with being one of the first to explore the concepts of heredity in a
scientific manner.
Slide 3
Gregor Mendel was born on July 22 in the year 1822 in Moravia, a village within what is now known as
the Czech Republic. Over the course of his childhood, he attended school and eventually the University
of Vienna in Austria while helping to support his family. By the age of 21, he decided to enter the clergy.
This allowed him to further his education and he was an ordained priest at the age of 25.
Slide 4
Mendel devoted much of his time to teaching in schools supported by the Brno monastery. It was
during Mendel’s teaching career that he was able to pursue his interests in biology and physics, and
conduct the experiments that led him to discover significant concepts within heredity.
Slide 5
Prior to Mendel’s experiments, there were many ideas concerning how traits were passed from parents
to offspring. These ideas drove the methods for breeding livestock put into effect by ranchers and
farmers. Despite the use of controlled breeding practices, it was still unclear how the traits were passed
on and combined within offspring, mainly because no other scientists had been able to successfully
research this concept.
Slide 6
Over the course of several years, Mendel bred thousands and thousands of pea plants in a controlled
fashion and these experiments led him to his discoveries. His experiments were well designed and
replicated numerous times, providing sets of data that could be mathematically analyzed. These
experiments advanced the study of heredity to the realm of scientific analysis.
Slide 7
Among the traits that Mendel examined were seed and pod colors and shapes, flower colors, and stem
heights. In order to control the reproduction of the pea plants, Mendel would first identify the
characteristics of a particular plant and confirm that it bred true for a particular trait.
Slide 8
For example, a tall plant, allowed to self pollinate, will always produce tall offspring if it is a truebreeding specimen.
Slide 9
Mendel would then crossbreed these true-breeding specimens by transferring pollen from one flower to
the pistil of another flower. He would allow the seeds to develop and then grow these seeds to observe
the characteristics of the resulting offspring.
Slide 10
There are three concepts that Mendel is credited with discovering through these experiments.
The first is the law of dominance. In order to discover dominant and recessive traits, Mendel crossbred
true-breeding plants with a contrasting trait. For example, in order to determine if height was a
dominant or recessive trait, he crossbred true-breeding tall plants with true-breeding short plants. As a
result, all of the offspring grew to be tall. This indicated that the tall characteristic was dominant over
the recessive characteristic for shortness. When Mendel allowed these offspring to self pollinate,
approximately one quarter of the offspring displayed the short characteristic. Using this pattern, which
he observed for all of recessive characteristics, he was able to develop the second concept: the law of
segregation.
Slide 11
In order for a trait to be hidden and then passed on to future offspring in the patterns that he observed,
Mendel determined that several processes must be taking place. First, every organism must carry two
factors that determine the manifestation of a particular characteristic. For example, a true-breeding tall
plant has two factors, now called alleles, for tallness. When an organism reproduces, it only passes on
one of each pair to its offspring. So in the case of the first generation of offspring in this experiment, the
allele that leads to the manifestation of the short characteristic was inherited by each offspring, but
hidden by the dominant tall allele that was inherited from the other parent.
Slide 12
When this generation of offspring reproduced, each individual had a 50 percent chance of passing on
the dominant or recessive allele to its offspring because of this concept of segregation.
Slide 13
A third concept that Mendel was able to discover through his experiments is the law of independent
assortment. This law states that the pairs of alleles for any characteristic will separate independently
from those that determine the characteristic of another trait. This causes all possible combinations of
alleles to be equally probable for the offspring. For example, if a parent plant has tall stems and round
peas, but carries the alleles for short stems and wrinkled peas, there are four different allele
combinations that could be passed on to the offspring, which are all equally probable.
Slide 14
In 1865, Mendel published the results of his experiments in a paper titled “Experiments in Plant
Hybridization,” though they were not immediately recognized for their significance. Because Mendel
was not a university professor and did not have a doctoral degree, his work did not attract much
attention. Given the fact that his research only involved this one particular species of organism, it was
also unclear at the time whether his conclusions could be universally applied to other organisms.
Two years after he published his results, Mendel was appointed abbot of the monastery and gave up
most of his teaching and scientific pursuits. Until his death in 1884 at the age of 61, Mendel’s primary
responsibilities were caring for and managing the monastery.
Slide 15
After his death and approximately 30 years after publishing his results, Mendel’s work was rediscovered
and his results were reaffirmed not only in pea plants but also in other organisms. The rediscovery of
Mendel’s work led to significant discoveries in genetics like the identification of genes and chromosomes
as the units of heredity, the discovery of sex chromosomes, and how changes in genes and the heredity
of traits lead to evolution.
Slide 16
The concepts that Mendel discovered using his pea plants are still relevant and researched today. For
example, there are over 10,000 genes in the human genome that follow Mendelian patterns of
inheritance in terms of dominant and recessive alleles. Among these are many diseases, referred to as
Mendelian disorders. These include disorders like Cystic Fibrosis and Huntington’s disease. What has
evolved into countless applications within medicine, agriculture, forensics, and many other disciplines,
began with the solitary pursuit of a monk within a monastery garden: Gregor Mendel, the father of
genetics.