Trends in Biotechnology
140320 – Foundations of
Modern Biotechnology
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Concept 1 - Children look similar to their
parents.
Gregor Mendel found that individual traits are
determined by discrete "factors," later known as
genes, which are inherited from the parents.
His research changed agricultural breeding
from an art to a science.
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He started with parents of known
genetic background — to provide a
baseline against which to compare
patterns of inheritance in the
resulting offspring.
Then he carefully counted the
numbers of individuals showing the
various traits in successive
generations of offspring.
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Mendel’s pea experiment:
http://www.dnaftb.org/1/animation.html
Mendel - genes come in pairs and are
inherited as distinct units, one from each
parent.
- parental genes segregate and appear in
the offspring as dominant or recessive
traits.
- there are mathematical patterns of
inheritance from one generation to the
next.
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Mendel's Laws of Heredity:
1) The Law of Segregation: Each inherited trait
is defined by a gene pair. Parental genes are
randomly separated to the sex cells so that sex
cells contain only one gene of the pair.
2) The Law of Independent Assortment: Genes
for different traits are sorted separately from
one another.
3) The Law of Dominance: An organism with
alternate forms of a gene will express the form
that is dominant.
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Concept 2 - Genes come in pairs.
Mendel - seven individual traits that he
could readily distinguish.
- each trait has two alternate forms. For
example, seed color can be green or
yellow.
- alternative form of a trait is specified by
alternative forms of a gene.
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Pea plants are naturally selffertilizing, "pure-bred" strains
were available.
Each strain contained only one
form of the gene that determined
a trait.
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Pure-bred plants with yellow seeds only
produced plants with yellow seeds.
Pure-bred plants with green seeds only
produced offspring with green seeds.
Mendel - pure-bred plants must
have two copies of the same gene
for each trait.
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Here is an animation of Mendel’s
experiment.
http://www.dnaftb.org/2/animation.html
To get a feel for Mendel’s experiments
you can do the problem at
http://www.dnaftb.org/2/problem.html
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Concept 3 - Genes don't blend.
Offspring appear to be a mixture of
parental characteristics.
Mendel - not true for the pea plant traits
that he chose to study.
Pure-bred pea plants when crossed did
not produce offspring with blended traits.
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Eg. a cross between purebred green-seeded and
pure-bred yellow-seeded
pea plants might produce
offspring with seeds of an
intermediate green-yellow
color. Color blending
happens when paint is
mixed together.
However, Mendel found
that this cross produced
offspring with only one
color — yellow.
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Here is an animation showing this
concept.
http://www.dnaftb.org/3/animation.html
Here is a problem to help you remember
the concept
http://www.dnaftb.org/3/problem.html
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Concept 4 - Some genes are dominant.
Mendel - genes behave like atoms from a
pure substance.
- Genes can combine in various ways,
but always maintain their distinct
identities.
Eg. cross two pure-bred parents with
different traits, the hybrid offspring would
have both the gene alternates for the trait.
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Why then do
offspring from
such a cross have
only yellow
seeds?
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Mendel - although both gene
alternates are present, there is no
blending of color because the
gene alternate for yellow is
"dominant" over the gene
alternate for green.
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When he crossed the hybrid
offspring, green seeds reappeared in
the next generation.
Mendel - "recessive" green trait is
shown only when a copy of the
recessive gene form is inherited from
both parents.
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Animation at
http://www.dnaftb.org/4/animation.html
A review problem is at
http://www.dnaftb.org/4/problem.html
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Concept 5 - Genetic inheritance follows
rules.
Mendel - sex cells (sperm and eggs)
contain only one parental gene of
each pair. The half-sets of genes
contributed by sperm and egg give a
whole set of genes in the offspring.
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Mendel - different gene
combinations from the parents
resulted in specific ratios of
dominant-to-recessive traits.
For example, a cross between two
yellow-seed hybrids produces three
times as many yellow seeds as green
seeds. This is Mendel's 3 to 1 ratio.
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Animation at
http://www.dnaftb.org/5/animation.html
A review problem is at
http://www.dnaftb.org/5/problem.html
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Concept 6 - Genes are real things.
Mendel's work was not accepted
until 1900, when three European
scientists independently confirmed
his results.
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There was strong evidence that cells are the
basic units of life.
Biological stains showed structures within cells
— including chromosomes.
Different organisms have different numbers of
chromosomes, suggesting that they might carry
information specific for each life form.
This study of the cell and chromosomal
behavior gave Mendel's genetic work a physical
basis.
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Animation at
http://www.dnaftb.org/6/animation.html
The review problem is at
http://www.dnaftb.org/6/problem.html
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Concept 7 - All cells arise from other cells.
The end of the idea of "spontaneous
generation" mid-1800s.
All life comes from pre-existing life —
by reproduction.
Cells have a way to reproduce that keeps
the proper chromosome number in each
cell.
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Scientists studied the behavior of
chromosomes during cell division (mitosis),
using dyes to make them visible.
Each chromosome copies itself and the
duplicates line up at the mid-line of the cell.
Then, duplicate copies of each chromosome
are pulled toward opposite ends of the cell.
Finally, the cell splits at the mid-line, producing
two new cells with identical sets of
chromosomes.
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Animation at
http://www.dnaftb.org/7/animation.html
The review problem is at
http://www.dnaftb.org/7/problem.html
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1882 - threads were visible in cells
during cell division, and equally
distributed to daughter cells. These
were chromosomes during the
process of mitosis (cell division).
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http://commons.wikimedia.org/wiki/File:Meiosis.png
1903 - chromosomes were found to
be the carriers of Mendel’s units of
heredity.
1909 – the word “genes” was first
used to name Mendel’s units of
inheritance.
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Concept 10 - Chromosomes carry genes.
Thomas Hunt Morgan showed the
physical basis of heredity.
- studied inheritance in the fruit fly.
- spent months searching for a fly with
any unique trait that could be studied.
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Finally they found a single whiteeyed male fly.
A cross between the mutant male
and a red-eyed female produced
only red-eyed offspring.
White-eyed mutants reappeared in
the following generation — the
classic pattern of a recessive trait.
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White-eyed trait was
only seen in males of
the second generation.
- white-eyed is a sexlinked recessive trait.
- The gene for eye
color is on the X
chromosome.
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Animation at
http://www.dnaftb.org/10/animation.html
The review problem is at
http://www.dnaftb.org/10/problem.html
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Concept 13 - Mendelian laws apply to
human beings.
Mendel's laws applied to all living
things.
Pedigrees of families affected by
diseases show examples of
Mendelian inheritance in humans.
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Recessive disorders
• alkaptonuria (1902) and
• albinism (1903).
Dominant disorders
• brachydactyly (short fingers, 1905),
• congenital cataracts (1906), and
• Huntington's chorea (1913).
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Sex-linked disorders
• Duchenne muscular dystrophy (1913),
• red-green color blindness (1914), and
• hemophilia (1916).
The simple concept of eye color
inheritance — brown is dominant, blue is
recessive (1907); now believe that several
genes are involved.
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Animation at http://www.dnaftb.org/13/an
imation.html
The review problem is at http://www.dnaft
b.org/13/problem.html
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