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Biol 1124 Gregor Mendel and Evolution Lecture Notes
- Course
- General Biology 1
- Institution
- Rose State College
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BIO NOTES - EVOLUTION● The science of genetics explains the stability of inheritance (why you are human,
as are your parents) as well as variations between offspring from one generation
to the next (why you have a different combination of traits than your parents).
● Virtually every culture in history has attempted to explain observed inheritance
patterns.
● An understanding of these patterns has always been important to agriculture,
animal husbandry (the science of breeding animals), and medicine.
The Blending Concept of Inheritance
● When Gregor Mendel began his work, most plant and animal breeders
acknowledged that both sexes contribute equally to a new individual.
● They thought that parents of contrasting appearance always produced offspring
of intermediate appearance - called the blending concept of inheritance, meant
that a cross between plants with red flowers and plants with white flowers would
yield only plants with pink flowers.
○ When red and white flowers reappeared in future generations, the
breeders mistakenly attributed this to instability in the genetic material.
○ The blending concept of inheritance offered little help to Charles Darwin,
the father of evolution
○ Darwin’s theory of natural selection was based on the fact that populations
possessed variation that allowed for certain individuals to have a selective
advantage. According to the blending concept, over time variation would
decrease as individuals became more alike in their traits.
● Mendel’s Particulate Theory of Inheritance
○ Gregor Mendel was an Austrian monk who developed a particulate theory
of inheritance after performing a series of ingenious experiments in the
1860s
○ Mendel studied science and math.ematics at the University of Vienna, and
at the time of his research in genetics, he was a substitute natural science
teacher at a local high school.
○ Mendel was a successful scientist for several reasons.
■ First, he was one of the first scientists to apply mathematics to
biology.
■ Most likely his background in mathematics prompted him to apply
statistical methods and the laws of probability to his breeding
experiments.
■ He was also a careful, deliberate scientist who followed the
scientific method very closely and kept very detailed, accurate
records.
, ■ He prepared for his experiments carefully and conducted many
preliminary studies with various animals and plants.
■ Mendel’s theory of inheritance is called a particulate theory
because it is based on the existence of minute particles, or
heredi.tary units, we now call genes.
■ Inheritance involves the reshuffling of the same genes from
generation to generation.
● The two laws he proposed, the law of segregation and the
law of independent assortment, which we will discuss shortly,
describe the behavior of these particulate units of heredity as
they are passed from one generation to the next.
● While Mendel did not know of DNA or genetic material, his
theories have been well supported by count.less
experiments of geneticists and molecular biologists.
Mendel Worked with the Garden Pea
● Mendel’s preliminary experiments prompted him to choose the garden pea,
Pisum sativum as his experimental organism. The garden pea was a good choice
for many reasons. The plants were easy to cultivate and had a short generation
time. Although peas normally self-pollinate (pollen only goes to the same flower),
they could be cross-pollinated by hand by transfer.ring pollen from the anther
(male part of a flower) to the stigma (female part of a flower).
● Many varieties of peas were available, and Mendel chose 22 for his experiments.
● When these varieties self-pollinated, over generations they became true-
breeding—meaning that all the offspring were the same and exactly like the
parent plants.
● Unlike his predecessors, Mendel studied the inheritance of relatively simple and
discrete traits that were not subjective and were easy to observe, such as seed
shape, seed color, and flower color.
● In his crosses, Mendel observed that the offspring did not possess intermediate
charactersitics but, rather, were similar in appearance to one of the parents.
● As we will see, this disproved the blending concept and supported the particulate
theory of inheritance.
Mendel’s Laws
● After ensuring that his pea plants were true-breeding—for example, that his tall
plants always had tall offspring and his short plants always had short offspring—
Mendel was ready to perform cross-pollination experiments inheritance were
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