DNA Profiling, Gel Electrophoresis, Cloning, and Gene Technology

Flashcards covering gel electrophoresis, DNA profiling, somatic cell nuclear transfer, reproductive and therapeutic cloning, the Human Genome Project, genetic engineering, and bioethics.

What is gel electrophoresis?

A laboratory process that separates fragments of DNA based on their sizes.

What are the three steps and temperatures involved in a standard cycle of Polymerase Chain Reaction (PCR)?

1. Denaturation at $94-95^\circ\text{C}$ (separates double-stranded DNA into single strands); 2. Annealing at $40-60^\circ\text{C}$ (primers bind complementary sequences on target DNA); 3. Extension at $70-74^\circ\text{C}$ (DNA polymerase extends primers to synthesize complementary strands).

What machine executes the cycles of PCR, and how many times are the steps typically repeated?

A thermocycler is used, repeating the three-step cycle $30$ to $40$ times to produce many DNA copies.

Why do DNA fragments migrate toward the positive electrode during gel electrophoresis?

DNA fragments carry a negative electrical charge due to their phosphate groups, causing them to move away from the negative well end toward the positively charged electrode.

How does agarose gel separate DNA fragments of differing sizes?

The porous gel matrix impedes larger DNA fragments more than smaller ones, allowing smaller fragments to travel faster and farther through the gel.

What are the key advantages and disadvantages of gel electrophoresis?

Pros: Easy to perform, does not ruin the DNA, requires only a small initial amount of DNA, and detects DNA of any size. Cons: Expensive, time-consuming, and utilizes hazardous materials.

What percentage of DNA is shared among all humans, and what fraction causes individual genetic differences?

Humans share approximately $99.9\%$ of their DNA with other humans; only $0.1\%$ accounts for individual differences.

According to this graph, how does the percentage of non-protein-coding DNA correlate with complexity among organisms?

Non-protein-coding sequences make up a small fraction in prokaryotes, but among eukaryotes, the proportion of non-coding DNA generally increases with organism complexity, exceeding $90\%$ in humans.

What are Short Tandem Repeats (STRs), and why are they selected for DNA profiling?

STRs are polymorphic regions of non-coding DNA containing repeats of identical nucleotide sequences (such as $\text{GATA}$ repeated six times); they are used because their lengths vary extensively between individuals.

How many genetic loci are examined during DNA profiling in Australia compared to the United States?

At least $10$ loci are examined in Australia, whereas $13$ STR sites are analyzed in the United States.

What is the statistical probability of two unrelated individuals sharing the identical profile across all 10 tested STR sites?

The probability is $1$ in hundreds of millions.

Why are buccal swabs preferred for collecting known reference DNA samples from suspects or victims?

Scraping the inside of the cheek yields abundant cellular DNA, is non-invasive, and is quick and easy to perform.

Based on this paternity testing diagram, how are DNA profiles evaluated to confirm or exclude paternity?

A child inherits bands from both biological parents; every band in the child's profile must match either the mother or the father. If non-maternal bands in the child do not match the man, he is excluded as the biological father.

Based on this forensic profile comparison, which suspect matches the evidence, and what does a match prove?

Suspect #2 matches every band of the crime scene DNA profile, proving that Suspect #2 was present at the crime scene at some point in time.

What are two critical procedural or evidentiary limitations associated with DNA profiling?

1. Sample contamination (failure to wear gloves and protective equipment can lead to wrongful accusation or conviction); 2. Profiling requires a known suspect sample or database entry for comparison.

What is the biological definition of a clone?

A genetically identical copy of a gene, cell, tissue, or organism.

What distinguishes reproductive cloning from therapeutic cloning?

Reproductive cloning creates a cloned whole organism via somatic cell nuclear transfer, whereas therapeutic cloning harvests embryonic stem cells after $4-5\text{ days}$ in culture to create patient-matched tissues without immune rejection.

Based on the somatic cell nuclear transfer procedure depicted for Dolly the sheep, what roles were played by the donor sheep?

The Finn-Dorset sheep served as the nuclear donor (providing the mammary cell nucleus), the Scottish Blackface served as the egg donor (providing the enucleated egg), and another Scottish Blackface served as the surrogate ewe.

In what year was Dolly the sheep cloned, and why was this event scientifically historic?

Dolly was cloned in $1996$, marking the first time a mammal was successfully cloned from an adult somatic cell.

Why is reproductive cloning considered an ineffective strategy for conserving endangered species?

It has an extremely low success rate of only $1\%$, requires hundreds of eggs, wild animal reproductive biology is poorly understood, and it does not resolve primary extinction threats like habitat loss and hunting.

What ethical dilemma is specifically central to therapeutic cloning using embryonic stem cells?

Harvesting embryonic stem cells destroys the early embryo, which many individuals and groups consider the destruction of a potential human life.

What is a genome?

An organism's complete set of DNA, including all of its genes, containing all the information required to build and maintain that organism.

How long did the Human Genome Project take, how much did it cost, and in what year was it completed?

It took $14\text{ years}$, cost $\$3\text{ billion}$, and was completed in the year $2000$.

How do modern computerized DNA sequencing speeds and expenses compare to the original Human Genome Project?

Modern computers can sequence a person's DNA within a few days at an approximate cost of $\$1000$.

What distinguishes genetic testing from genetic screening?

Genetic testing is targeted at individuals with a known family history of a specific genetic disorder (such as cystic fibrosis), whereas genetic screening is routinely administered across large populations regardless of family history (such as the PKU test on newborns).

What is the normal biological role of the BRCA1 gene, and what happens when it undergoes mutation?

BRCA1 is a tumor suppressor gene encoding a protein that repairs DNA or destroys cells with irreparable DNA damage; mutations impair this repair function, significantly increasing the risk of breast cancer.

What functions do restriction enzymes and DNA ligases perform during genetic modification?

Restriction enzymes act as molecular 'scissors' that cut DNA at specific nucleotide recognition sequences, while DNA ligases act as 'glue' that pastes DNA strands together.

What was the first genetically modified organism (GMO), and in what year was it created?

The first GMO was a bacterium created in $1973$.

Which genes were introduced into Golden Rice, and what medical condition was it engineered to prevent?

Two genes from daffodils and one from a bacterium were introduced into the rice genome to produce enzymes that synthesize vitamin A, aiming to prevent blindness among malnourished populations.

According to this diagram, what are the three steps required to engineer pest-resistant Bt crops?

1. Isolate Bacillus thuringiensis soil bacteria; 2. Use enzymes to extract the Bt gene that codes for a caterpillar-specific toxin; 3. Incorporate the Bt gene into crop chromosomes (such as cotton and corn) so feeding caterpillars die.

What is the definition of a 'designer baby'?

A baby whose genetic make-up has been deliberately altered using genetic engineering to ensure the presence or absence of particular genes or traits.

What are the four core ethical principles evaluated when considering genetic technologies?

1. Beneficence (who benefits and in what way); 2. Non-maleficence (who might be harmed and how harm is minimized); 3. Individual rights (respecting personal autonomy and rights); 4. Justice and equity (fair distribution of benefits and prevention of discrimination).