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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.

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 self-fertilizing, "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 pure-bred 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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36http://commons.wikimedia.org/wiki/File:Meiosis.png

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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.

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 white-eyed 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. 40

White-eyed trait was only seen in males of the second generation. - white-eyed is a sex-

linked 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/animation.html The review problem is at http://www.dnaftb.org/13/problem.html

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