Genetics – Human Genetic Disorders and Genetic

Engineering

Karyotypes• Pictures of chromosomes, cut out and

placed in order of size and location of centromere. Placed in homologous pairs.

Normal male karyotype

Can show chromosomal problems:

• Down Syndrome: Trisomy 21; mental retardation, many physical differences

Turner Syndrome – female, small stature, infertile

Klinefelter Syndrome – male, tall stature, infertile

These disorders result from NONDISJUNCTION

• Failure of chromosomes to separate normally during meiosis – – Eggs or sperm get one too many chromosomes

or one too few.– Ex – Down syndrome has one extra #21– Klinefelter has one extra X chromosome– Turner has one too few – only one X

Other Human Disorders• Sickle Cell Anemia –

– autosomal recessive– Found most often among people of African

ancestry– Blood cells sickle (change shape) when

oxygen-deprived (exertion, increase in altitude)– Causes sickle cell event – pain and immobility

and death of tissue ( dangerous if in organ)– Treatment – hospitalization and oxygen– Carriers are resistant to malaria

Tay Sachs Disease

• Autosomal recessive

• Found most often among Jews of Mediterranean ancestry

• Child born appearing normal, but fat builds up in brain and child dies by age 5

• No treatment, no cure

Huntington Disease

• Autosomal dominant– Symptoms do not appear until age 30-40.– Death takes about 5-10 years– No treatment, no cure – but there is a test to see

if you have it before symptoms begin– Results in mental impairment and

uncontrollable spastic movements

Phenylketonuria - PKU

• Person can’t breakdown phenylalanine (one of the 20 amino acids)

• OK when born, but if phenylalanine not restricted by diet, mental retardation will result, getting worse the longer phenylalanine is in the diet.

• Diet prevents PKU

Aneuploidy – incorrect number of chromosomes

• Down Syndrome

• Turner Syndrome

• Klinefelter Syndrome

Deletions

• Chromosome fragment breaks off and is lost

• Cri du chat syndrome – mental retardation and many physical problems

Prenatal Tests to detect chromosomal problems:

• Amniocentesis – removes a little amniotic fluid from around baby – fluid is then tested for abnormal proteins and the cell in it can be karyotyped.

• Risk of miscarriage

Chorionic Villus Sampling

• Take a piece of the chorionic villus from the placenta – it is made of baby cells – and test as in amniocentesis – Can be done earlier than amniocentesis– Risk of miscarriage– Has been linked to deformed fingers

Ultrasound• Only truly noninvasive test – sound waves

supply a view of the baby – can see many physical deformities

• Totally risk free

Bioethical Dilemma

• Once a prenatal diagnosis of a genetic disorder is made, what are the parents to do?– Do nothing and give birth to child with disorder– Abort embryo/fetus

• Who should make the decision?

•What should enter into making the decision?

Genetic Counseling

• Genetic counselor:– educates the parents about the disorder,– tells them of their options without influencing

their decision, – and tells them of the consequences of each

option

Genetic Engineering

• We can manipulate DNA and genes to alter organisms or make them produce a product we need.

Recombinant DNA – DNA from two different sources joined together.

1. Cut the DNA and the plasmid using the same restriction enzyme (these enzymes recognize the same base sequences.

2. Insert the foreign DNA into the plasmid.

3. Replace the plasmid into the bacterium

4. Allow the bacterium to reproduce – all future generations have the new DNA

5. Collect the product – it might be insulin or growth hormone, or some other molecule.

III. Cloning and the Wider World of Biotechnology (Section 15.3)

A. Definition of Cloning—To make an exact genetic copy of; can be a gene, a cell, or an entire organism.

B. How Dolly was cloned

1.In 1997 by researcher Ian Wilmut and colleagues at PPL Therapeutics.

2.Figure 15.6 is Animated in the Chapter 15 Media Lab.

a) A cell was taken from udder of adult sheep and grown in culture in a laboratory to create many daughter cells.

b) An egg was taken from another sheep, and its nucleus was removed.

c) The udder cell and the denucleated egg were fused by electricity, stimulating the egg to develop as if it had been fertilized using the diploid udder cell nucleus instead of the sperm and egg nuclei.

d) The embryo that developed was implanted into a surrogate mother sheep, and was born as Dolly, with the exact DNA from the original udder cell.

C. Benefits of cloning—Wilmut and colleagues were not just interested in cloning on its own; instead, they wanted to combine cloning with recombinant DNA technology for a variety of benefits:

1.Creating livestock that contain human genes needed to treat genetic disorders like hemophilia (Factor VIII).

2.Creating livestock to serve as organ donors, or blood donors.

IV. PCR—Polymerase Chain Reaction (Section 15.4)A. Used to “amplify”—make large amounts of a

specific piece of DNA from a very small sample.

B. Technique: Figure 15.71.Heat a starting quantity of DNA to

separate the double helix.

2.Add a collection of all four nucleotides, and DNA polymerase to copy the DNA, and some primers, and cool the sample.

3. Primers are short sections of DNA that are complementary to the region on both ends of the DNA that you wish to copy. Primers act as signals to tell DNA polymerase where to copy. As the solution cools, they stick to the DNA you wish to copy and allow polymerase to do its job.

4. Heating the sample again unwinds the new duplicated strands; cooling again allows more primers to bind. If you repeat this as a cycle, you can make millions of copies of the original DNA. (Interactive Activity 2)

V. Visualizing DNA Sequences (Section 15.5)A. So many bases, it is best to visualize them all in some

organized fashion.

1. Restriction enzymes can be used to cut the chromosomes from many cells into manageable pieces.

2. There will be a collection of copies of fragment 1, which is a different size than fragment 2, and so on.

3. The pieces can be ordered according to size using gel electrophoresis (moving the fragments in an electric field through a gel matrix). Larger pieces are more easily retarded by holes in the gel, so they travel less than smaller pieces: Figure 15.8

4. Animation: DNA Tool kit from Chapter 15 Media Lab: gel electrophoresis

5. Dyes that bind DNA can then be used to visualize the fragments as bands that can be compared to reference DNA fragments of known size.

B. Sequencing DNA

1.Characterizing a stretch of DNA by the order of As, Gs, Cs, and Ts.

2.Regularly performed by machine.

C. Sidebar—“DNA in the Courtroom”

1.Use of VNTRs (variable number of tandem repeats; different individuals have different numbers of repetitive stretches of DNA, for example, GGAGG). One individual might have 6, another 12.

2.VNTRs can be analyzed by gel electrophoresis, creating a banding pattern specific to each individual—like a bar code (Interactive Activity 3)

VI. The Human Genome Project (Section 15.6)A. Massive undertaking to locate and

catalogue every bit of genetic information in the human genome.

B. Budget of $300 million in 1998C. Limitations:

1.Knowing all the sequence is not the same as knowing what all the genes do,

2.Just a good reference point to start. (Interactive Activity 4)

VII. Uses of Biotechnology (Section 15.7)A. Biopharmaceuticals: Table 15.1—drugs

produced from recombinant DNA technology

B. Human Gene Transfer—gene therapy, replacing defective gene with a working one to treat genetic conditions1.Insert gene into vectors which will allow it

to be added to human cells.

2.Best cells to infect are stem cells.3.Problems—specificity, triggering immune

response, keeping cells producing the protein over generations.

C. Biotechnology and food:

1.Boost milk production 25 percent in cows with bovine growth hormone made in bacteria.

2.Fast-growing salmon: Figure 15.10

C. Biotechnology and food:

3.Genetically altered crops—First came to market in 1994, by 1998 there were 45 million acres in production. Two categories of genetic alterations:

a) Added genes for herbicide resistance

b) Added genes for killing pests: Figure 15.11 (Bacillus thuringensis Bt toxin). Concerns about insects building resistance, plants passing genes to wild relatives, or inadvertently killing off beneficial insects like butterflies. (Interactive Activity 5)

D. Benefits of DNA sequence knowledge for understanding evolution.

VIII. Ethical Questions in Biotechnology (Section 15.8)A. Five percent of the Human Genome Project is

devoted to ethical ramifications

1.Ethical to modify humans, how far should we go? Chickens without legs or eyes?

2.Will biotech produce new harmful organisms?

3.Are biotech diagnoses running far ahead of treatments?

4.Genetic discrimination? Who can have access to this information?