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Genetic EngineeringGene Expression &Mutations

Review

+Human Genome Human Genome - Our

complete set of genetic information. Includes tens of thousands

of genes. By 2000, the DNA sequence

of the human genome was almost complete.

Biologists were able to identify genes that directly control a single human trait.

+Tracing Traits Some of the most obvious human traits are almost

impossible to associate with single genes. Two reasons why:

1. Things you might think of as single traits (such as the shape of your eyes or ears) are actually controlled by many genes.

2. Many of your personal traits are only partly governed by genetics. Many traits are strongly influenced by environmental factors, including nutrition and exercise.

Example: Nutritional improvements in the US and Europe have increased the average height of these populations about 10 cm. over their average height in the 1800s.

+Genetic Tests Genetic tests are now

available for hundreds of disorders. Making it possible to

determine whether prospective parents risk passing such alleles to their children.

DNA testing can pinpoint the exact genetic basis of a disorder, making it possible to develop more effective treatment for individuals affected by genetic disease.

+Genetic Disorders: Recessive Alleles Many disorders are caused by recessive

alleles. Examples include:

1. Albinism2. Cystic fibrosis3. Tay-Sachs disease

+Genetic Disorders: Dominant Alleles Some genetic disorders are caused by

dominant alleles. If you have a dominant allele for a

genetic disorder, it will be expressed (even if the recessive allele is present).

Examples include:1. Achondroplasia (Dwarfism)2. Huntington’s Disease (nervous system disorder)3. Hypercholesterolemia (excess cholesterol in blood)

+Sex-Linked Genes

Genes located on the sex chromosomes are said to be sex-linked genes. More than 100 sex-linked genetic disorders

have now been mapped to the X chromosome.

The human Y chromosome is much smaller than the X chromosome and appears to contain only a few genes.

+Expression of X-Linked GenesMales have just one X chromosome. Thus,

all X-linked alleles are expressed in males, even if they are recessive.

In order for a recessive allele to be expressed in females, there must be two copies of the allele (one on each of the two X chromosomes).

Females are also the only sex that can be a carrier of the trait. They do not express it but could “carry” that trait to their offspring

+Examples of Sex-Linked Genes1. Colorblindness2. Hemophilia

About 1 in 10,000 males is born with a form of hemophilia.

3. Duchenne Muscular Dystrophy

1 out of every 3000 males is born with this condition. 

+Chromosomal DisordersThe most common error in

meiosis occurs when homologous chromosomes fail to separate. This is known as

nondisjunction, which means “not coming apart.”

+Karyotype Karyotype - Set of photographs of chromosomes

grouped in order in pairs. Cell biologists photograph cells in mitosis when

the chromosomes are fully condensed and easy to see.

Then the chromosomes are cut from the photographs and grouped together in pairs.

+Pedigree Chart Pedigree Chart - Chart that shows the relationships

within a family Tool for tracing a trait through generations of a

family. Used to predict whether a person is a carrier of a

heredity disease.

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Genetic Engineering

+Genetic VariationYou can compare dogs

of every breed imaginable!

There is an enormous range of characteristics that are the result of genetic variation.

+Selective BreedingWe did it.

Humans have kept and bred dogs for thousands of years, always looking to produce animals that might be better hunters, better retrievers, or better companions.

By selective breeding, allowing only those animals with desired characteristics to produce the next generation, humans have produced many different breeds of dogs.

+Selective Breeding

Humans use selective breeding, which takes advantage of naturally occurring genetic variation in plants, animals, and other organisms, to pass desired traits on to the next generation of organisms.

+Selective BreedingThe ancestor of

modern corn had tiny kernels, each protected by a tough husk.

+Hybridization

Hybridization - Breeding technique that involves crossing dissimilar individuals to bring together the best traits of both organisms.

Hybrids, the individuals produced by such crosses, are often hardier than either of the parents.

+Inbreeding

Inbreeding is the continued breeding of individuals with similar characteristics.

The many breeds of dogs—from beagles to poodles—are maintained by inbreeding. Inbreeding helps to ensure that the characteristics that make each breed unique will be preserved.

+Risks of Inbreeding Although inbreeding is useful in retaining a

certain set of characteristics, it does have its risks.

Most of the members of a breed are genetically similar because of this, there is always a chance that a cross between two individuals will bring together two recessive alleles for a genetic defect.

Serious problems in many breeds of dogs, including blindness and joint deformities in German shepherds and golden retrievers, have resulted from excessive inbreeding.

+Increasing Variation

 

Breeders can increase the genetic variation in a population by inducing mutations by using radiation and chemicals, which are the ultimate source of genetic variability.

+Producing New Kinds of Plants Drugs that prevent

chromosomal separation during meiosis have been particularly useful in plant breeding.

Sometimes these drugs produce cells that have double or triple the normal number of chromosomes.

Plants grown from such cells are called polyploid because they have many sets of chromosomes.

Polyploidy: the condition of having three, four, or more sets of chromosomes instead of the two present in diploids.

+Polyploidy Polyploidy is usually fatal in animals. However, for reasons that are not clear, plants are

much better at tolerating extra sets of chromosomes.

Polyploidy may instantly produce new species of plants that are often larger and stronger than their diploid relatives.

+Genetic EngineeringGenetic Engineering - Process of

making changes in the DNA code of living organisms.Includes:

1. DNA Extraction The cells are opened and the

DNA is separated from the other cell parts.

2. Cutting DNA3. Separating DNA

+Genetic Engineering: Cutting DNA DNA molecules from

most organisms are much too large to be analyzed, so biologists cut them precisely into smaller fragments using restriction enzymes and each one cuts DNA at a specific sequence of nucleotides.

+Genetic Engineering: Separating DNA Gel electrophoresis - Procedure

used to separate and analyze DNA fragments by placing a mixture of DNA fragments at one end of a porous gel and applying an electrical voltage to the gel When the power is turned on,

DNA molecules, which are negatively charged, move toward the positive end of the gel.

The smaller the DNA fragment, the faster and farther it moves.

+Gel Electrophoresis

+DNA FINGERPRINTING:

+

In paternity testing, the child’s fingerprint will partly match mom’s bands, and partly

match dad’s bands.

+Recombinant DNA

Recombinant DNA - DNA produced by combining DNA from different sources.

+Transformation During transformation, a cell takes in DNA from outside

the cell. This external DNA becomes a component of the cell's DNA.

The live nonpathogenic bacteria took up DNA from the heat-killed pathogenic bacteria and were therefore pathogenic and killed the mice.

+Bacteria Transformation

+Transgenic Organisms Transgenic - Term used to

refer to an organism that contains genes from other organisms.

In 1986, American researcher Steven Howell transferred the gene for luciferase into tobacco plant cells. Luciferase is an enzyme

that allows fireflies to glow. The plants glowed in the

dark!

+Transgenic Organisms1. Transgenic Bacteria Reproduce rapidly and are easy to grow. Produce a host of important substances cheaply and in great

abundance. Examples are insulin, growth hormone, and clotting factor which are used to treat serious human diseases and conditions.

2. Transgenic AnimalsUsed to study genes and to improve the food supply. Mice have been produced with human genes that make their

immune systems act similarly to those of humans. Allows scientists to study the effects of diseases on the

human immune system. Some transgenic livestock now have extra copies of growth

hormone genes. Grow faster and produce leaner meat

+Transgenic Organisms3. Transgenic Plants

Are now an important part of our food supply.

In the year 2000, 52% of the soybeans and 25% of the corn grown in the US were transgenic, or genetically modified (GM).

Some GM plants contain genes that produce a natural insecticide. The crops do not have to be

sprayed with synthetic pesticides. Other crop plants have genes that

enable them to resist weed-killing chemicals. Allows crops to survive while weeds

are still controlled.

+Cloning

Clone - Member of a population of genetically identical organisms produced from a single cell. Bacteria and other microorganisms are easy to grow, but this is not always true of multicellular organisms, especially animals.

+Cloning Animals Clone - Member of a population of genetically

identical organisms produced from a single cell. Bacteria and other microorganisms are easy to grow, but this is not always true of multicellular organisms, especially animals.

In 1997, Scottish scientist Ian Wilmut stunned biologists by announcing that he had cloned a sheep, which he later named Dolly.

How did he do it? 1. The nucleus of an egg cell is

removed. 2. The cell is fused with a cell taken

from another adult. 3. The fused cell begins to divide and

the embryo is then placed in the reproductive system of a foster mother, where it develops normally.

+

Mutations

+• A point mutation is a change in a single

base pair in DNA.

• Result: A change in a single nitrogenous base can change the entire structure of a protein causing it to not function properly.

Types of Mutations

THE DOG BIT THE CAT. THE DOG BIT THE CAR.

• Does this one letter change the meaning of the entire sentence?

+A point mutation takes place when a singlenitrogenous base (letter) is changed at one

point.

Types of Mutations

THE DOG BIT THE CAT. THE DOG BIT THE CAR.

What would happen if a single nitrogenous base (letter) is deleted?

THE DOG BIT THE CAT. THD OGB ITT HEC AT.

Is this a problem?

WHAT HAPPENED?

+• A mutation in which a single base is added

or deleted from DNA is called a frameshift mutation because all the codons shift down by one base.

Deletion of U

Types of Mutations

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• Many mutations are caused by factors in the environment, such as radiation, chemicals, and

even high temperatures.

Causes of Mutations

• Any external agent that can cause a change in DNA is called a mutagen.

+ Repairing DNA• Enzymes proofread the DNA and replace

incorrect nucleotides with correct nucleotides.

• These repair mechanisms work extremely well, but they are not perfect.

• The greater the exposure to a mutagen such as UV light, the more likely that a mistake will not

be corrected.