Swarnendu Ghosh
22MS170
History
of
Biology
and
Genetics
Contents
Prehistoric Evidences
3
Discovery Of Cell (1665)
4
Anton van Leeuwenhoek (1677)
5
Cell eory (1839)
6
eory Of Evolution (1859)
7
Mendelian Inheritance (1860s)
8
Discovery Of DNA as Genetic Material (1940)
9
Discovery of the structure of DNA (1953)
10
Human Genome Project (HGP) (1990-2003)
11
3
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“In biology, nothing is clear, everything is too complicated, everything is a mess, and just
when you think you understand something, you peel off a layer and find deeper complications
beneath."
­ Richard Dawkins
Prehistoric Evidences
• Selective breeding of both plants and animals has been practiced since early Prehistory ;
key species such as wheat, rice, and dogs have been significantly different from their wild
ancestors for millennia, and maize, which required especially large changes from Teosinte,
its wild form, was selectively bred in Mesoamerica. Selective breeding was practiced by the
Romans.
• This Chihuahua mix and Great Dane
shows the wide range of dog breed sizes
created using selective breeding.
Figure 1: Chihuahua mix and Great
Dane
• Selective breeding has transformed
Teosinte (few fruitcases left) into modern
maize rows of exposed kernels (right)
Figure 2: Teosinte and Modern Maize
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Discovery Of Cell (1665)
• The Cell was first discovered by Robert
Hooke in 1665 , which can be found to
be described in his book Micrographia .
In this book, he gave 60 observations in
detail of various objects under a coarse,
compound microscope.
Figure 3: Robert Hooke’s Compound
Microscope
• One observation was from very thin slices
of bottle cork. Hooke discovered a multi­
tude of tiny pores that he named "cells" .
This came from the Latin word Cella,
meaning ‘a small room’ like monks lived
in, and also Cellulae , which meant the
six­sided cell of a honeycomb..
Figure 4: Drawing of the structure of
cork by Robert Hooke that appeared
in Micrographia
• However, Hooke did not know their real structure or function. What Hooke had thought were
cells, were actually empty cell walls of plant tissues. With microscopes during this time hav­
ing a low magnification, Hooke was unable to see that there were other internal components
to the cells he was observing. Therefore, he did not think the “cellulae" were alive. His cell
observations gave no indication of the nucleus and other organelles found in most living cells.
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Anton van Leeuwenhoek (1677)
• Using single­lensed microscopes of his
own design and make, Van Leeuwen­
hoek was the first to observe and to
experiment with microbes, which he orig­
inally referred to as dierkens, diertgens
or diertjes (Dutch for "small animals"
[translated into English as animalcules,
from Latin animalculum = “tiny ani­
mal” ])
Figure 5: A replica of a Microscope by
Van Leeuwenhoek
• He was the first to relatively determine
their size. Most of the animalcules are
now referred to as unicellular organ­
isms , although he observed multicellular
organisms in pond water. He was also
the first to document microscopic ob­
servations of muscle fibers, bacteria,
spermatozoa, red blood cells, crystals in
gouty tophi , and among the first to see
blood flow in capillaries .
Figure 6: A microscopic section
of a one­year­old ash tree (Fraxi­
nus) wood, drawing made by Van
Leeuwenhoek
• Van Leeuwenhoek’s main discoveries are:
1.
2.
3.
4.
5.
infusoria (protists in modern zoological classification), in 1674
bacteria, (e.g., large Selenomonads from the human mouth), in 1683
the vacuole of the cell
spermatozoa, in 1677
the banded pattern of muscular fibers, in 1682
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Cell Theory (1839)
• In biology, cell theory is a scientific the­
ory first formulated in the mid­nineteenth
century, that organisms are made up of
cells , that they are the basic structural/
organizational unit of all organisms, and
that all cells come from pre­existing cells.
Cells are the basic unit of structure in all
organisms and also the basic unit of repro­
duction .
The three tenets of the cell theory are:
• All organisms are composed of one or
more cells.
• The cell is the basic unit of structure
and organization in organisms.
• Cells arise from pre­existing cells.
Figure 7: Matthias Jakob Schleiden
(1804–1881)
Credit for developing cell theory is usually
given to two scientists: Theodor Schwann
and Matthias Jakob Schleiden.
• The generally accepted parts of modern
cell theory include:
1. All known living things are made up of
one or more cells.
2. All living cells arise from pre­existing
cells by division.
3. The cell is the fundamental unit of
structure and function in all living or­
ganisms.
4. The activity of an organism depends
on the total activity of independent
cells.
5. Energy flow (metabolism and biochem­
istry) occurs within cells.
6. Cells contain DNA which is found
specifically in the chromosome and
RNA found in the cell nucleus and cyto­
plasm.
Figure 8: Theodor Schwann (1810–
1882)
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Theory Of Evolution (1859)
• The theory of descent with modifica­
tion (or "theory of evolution by common
descent") essentially postulates that all or­
ganisms have descended from common
ancestors by a continuous process of
branching .
In other words, all life evolved from one
kind of organism or from a few simple
kinds, and each species arose in a single
geographic location, from another species
that preceded it in time. Evolutionists have
marshaled substantial evidence for the the­
ory of descent with modification.
That is, the "pattern of evolution" is
documented by the fossil record, the
distribution patterns of existing species,
methods of dating fossils, and comparison
of homologous structures , among others.
Figure 9: Darwin, c. 1854, when
he was preparing On the Origin of
Species
• The second theory of Darwin, the “theory of modification through natural selection” (or,
simply, “theory of natural selection”), holds that natural selection is the directing or cre­
ative force of evolution. It recognizes that individuals in a population are not all the same
(there are variations), some of these variations are heritable, all organisms produce more off­
spring than can survive, and those surviving to reproduce have the best fit to the environment,
such that favorable traits will accumulate and unfavorable traits will decline and be lost—
perhaps to the extent that a new species will be formed.
• Darwin strived to establish the “fact of evolution," countering the view of most people and
scientists at the time that the world was constant. Darwin also looked at speciation as a
populational phenomenon; the population gradually changed until it became a new species.
Thirdly, Darwin also insisted that evolution was entirely gradual, that evolution proceeded by
means of the slow, steady accumulation of slight favorable variations.
• Indeed, he stated in the Origin of Species:
1. “As natural selection acts solely by accumulating slight, successive, favourable variations,
it can produce no great or sudden modifications; it can act only by very short and slow
steps.”
2. “If it could be demonstrated that any complex organ existed, which could not possibly
have been formed by numerous, successive, slight modifications, my theory would ab­
solutely break down.”
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Mendelian Inheritance (1860s)
• The principles of Mendelian inheritance
were named for and first derived by
Gregor Johann Mendel , a nineteenth­
century Moravian monk who formulated
his ideas after conducting simple hybridi­
sation experiments with pea plants (Pisum
sativum) he had planted in the garden of
his monastery.
Mendel selected for the experiment the
following characters of pea plants:
1. Form of the ripe seeds (round or
roundish, surface shallow or wrinkled)
2. Colour of the seed–coat (white, gray,
or brown, with or without violet spot­
ting)
3. Colour of the seeds and cotyledons
(yellow or green)
4. Flower colour (white or violet­red)
5. Form of the ripe pods (simply inflated,
not contracted, or constricted between
the seeds and wrinkled)
6. Colour of the unripe pods (yellow or
green)
7. Position of the flowers (axial or termi­
nal)
8. Length of the stem
Figure 10: Gregor Mendel, the Mora­
vian Augustinian monk who founded
the Modernenum science of Genetics
Law
Definition
Law of dominance and uniformity
Some alleles are dominant while others are reces­
sive; an organism with at least one dominant allele
will display the effect of the dominant allele
Law of segregation
During gamete formation, the alleles for each gene
segregate from each other so that each gamete car­
ries only one allele for each gene.
Law of independent assortment
Genes of different traits can segregate indepen­
dently during the formation of gametes.
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• 1. Characters are unitary, that is, they
are discrete. There is no medium­sized
plant or lienumght purple flower.
2. Genetic characteristics have alternate
forms, each inherited from one of two
parents. Today these are called alleles.
3. One allele is dominant over the other.
The phenotype reflects the dominant al­
lele.
4. Gametes are created by random segre­
gation. Heterozygotic individuals pro­
duce gametes with an equal frequency
of the two alleles.
Figure 11: Myosotis: Colour and
distribution of colours are inherited
independently
Discovery Of DNA as Genetic Material (1940)
• The Avery–MacLeod–McCarty experi­
ment was an experimental demonstration,
reported in 1944 by Oswald Avery, Colin
MacLeod, and Maclyn McCarty, that
DNA is the substance that causes bacterial
transformation, in an era when it had been
widely believed that it was proteins that
served the function of carrying genetic in­
formation .
It was the culmination of research in the
1930s and early 20th century to purify
and characterize the "transforming prin­
ciple" responsible for the transformation
phenomenon first described in Griffith's
experiment of 1928:
killed Streptococcus pneumoniae of the
virulent strain type III­S, when injected
along with living but non­virulent type
II­R pneumococci, resulted in a deadly in­
fection of type III­S pneumococci. .
Figure 12: Hyder, Avery, MacLeod
and McCarty used strands of purified
DNA such as this, precipitated from
solutions of cell components, to per­
form bacterial transformations
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• The Hershey–Chase experiments were
a series of experiments conducted in 1952
by Alfred Hershey and Martha Chase that
helped to confirm that DNA is genetic
material .
While DNA had been known to biologists
since 1869, many scientists still assumed
at the time that proteins carried the in­
formation for inheritance because DNA
appeared to be an inert molecule, and,
since it is located in the nucleus, its role
was considered to be phosphorus storage.
Figure 13: Scientist Martha Chase
and Alfred Hershey
In their experiments, Hershey and Chase
showed that when bacteriophages, which
are composed of DNA and protein, in­
fect bacteria, their DNA enters the host
bacterial cell, but most of their protein
does not.
Hershey and Chase and subsequent dis­
coveries all served to prove that DNA is the
hereditary material .
Discovery of the structure of DNA (1953)
• Molecular Structure of Nucleic Acids:
A Structure for Deoxyribose Nucleic
Acid was the first article published to de­
scribe the discovery of the double helix
structure of DNA , using X­ray diffraction
and the mathematics of a helix transform.
This article is often termed a "pearl" of
science because it is brief and contains
the answer to a fundamental mystery about
living organisms.
This mystery was the question of how it is
possible that genetic instructions are held
inside organisms and how they are passed
from generation to generation.
Figure 14: Diagramatic representation
of the key structural features of the
DNA double helix.
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• It is not always the case that the structure
of a molecule is easy to relate to its func­
tion. What makes the structure of DNA
so obviously related to its function was
described modestly at the end of the arti­
cle: “It has not escaped our notice that
the specific pairing we have postulated
immediately suggests a possible copying
mechanism for the genetic material".
The specific pairing is a key feature of
the Watson and Crick model of DNA, the
pairing of nucleotide subunits. In DNA,
the amount of guanine is equal to cyto­
sine and the amount of adenine is equal to
thymine.
After realizing the structural similarity of
the A:T and C:G pairs, Watson and Crick
soon produced their double helix model of
DNA with the hydrogen bonds at the core
of the helix providing a way to unzip the
two complementary strands for easy repli­
cation: the last key requirement for a likely
model of the genetic molecule.
Figure 15: DNA replication. The two
base­pair complementary chains of
the DNA molecule allow replication
of the genetic instructions.
Human Genome Project (HGP) (1990­2003)
• The Human Genome Project (HGP)
was an international scientific research
project with the goal of determining the
base pairs that make up human DNA,
and of identifying, mapping and sequenc­
ing all of the genes of the human genome
from both a physical and a functional
standpoint. It started in 1990 and ended on
2003.
It remains the world’s largest collabo­
rative biological project.
Figure 16: Logo of the Human
Genome Project.