Heredity

What is the primary outcome of DNA replication?

The production of exact copies of DNA with identical base sequences.

DNA replication is described as _ because each new molecule consists of one original template strand and one newly synthesised strand.

semi-conservative

Which enzyme unwinds and separates the two DNA strands by breaking hydrogen bonds during replication?

Helicase.

Which enzyme covalently joins free nucleotides together to form a complementary strand during DNA replication?

DNA polymerase.

What type of bond does DNA polymerase catalyse the formation of between a sugar and a phosphate group?

A phosphodiester bond.

Why is DNA replication initiated at multiple points simultaneously in long DNA molecules?

To limit the time required for the entire process of replication to occur.

What is the Polymerase Chain Reaction (PCR)?

An artificial method of DNA copying that uses a thermal cycler to rapidly amplify a specific DNA sequence.

Which heat-tolerant enzyme, isolated from 'Thermus aquaticus', is used in PCR?

Taq polymerase.

What occurs during the Denaturation step of PCR, and at what temperature?

The DNA is heated to separate the two strands, typically at 90ºC.

What is the purpose of the Annealing step in PCR, which occurs around 55ºC?

Primers bind to the separated DNA strands to designate the region to be copied.

During which step of PCR does Taq polymerase copy the DNA strands, and at what approximate temperature?

The Extension step, which occurs at approximately 75ºC.

What is gel electrophoresis used for?

It is a laboratory technique used to separate DNA or proteins based on their size.

In gel electrophoresis, why does DNA move towards the positive anode?

Because DNA is negatively charged due to its phosphate groups.

In gel electrophoresis, do smaller or larger DNA fragments move faster and further through the gel?

Smaller samples are less impeded and therefore move both faster and further.

What is DNA profiling?

A technique by which individuals can be identified and compared via their respective DNA profiles.

What are the repeating elements in non-coding regions of DNA, used in profiling, called?

Short Tandem Repeats (STRs).

What are the three main steps in the procedure for DNA profiling?

1. DNA amplification using PCR, 2. Cutting STR loci with restriction enzymes, 3. Separation of fragments by gel electrophoresis.

In a paternity test, what is the rule for matching bands in the infant's DNA profile?

Every band present in the DNA profile of the infant must come from one of the parents.

The cell cycle is an ordered set of events resulting in the division of eukaryotic cells and involves which two key phases?

Interphase and the M phase.

During which stage of interphase does DNA replication occur?

The S (synthesis) stage.

What happens during the G1 stage of interphase?

The cell grows and prepares for division by duplicating its organelles.

The M phase of the cell cycle consists of nuclear division, called , and cytoplasmic division, called .

mitosis (or meiosis); cytokinesis

In what uncondensed form is DNA normally packaged within eukaryotic cells to allow access to genetic instructions?

Chromatin.

When DNA is replicated during the S phase, the resulting two identical DNA molecules held by a centromere are called _.

sister chromatids

What is the process of nuclear division where duplicated DNA molecules are arranged into two separate nuclei?

Mitosis.

During which phase of mitosis do chromosomes condense and the nuclear membrane dissolves?

Prophase.

What is the key event of metaphase in mitosis?

Chromosomes align along the middle (equator) of the cell.

What happens to sister chromatids during anaphase of mitosis?

They separate and are moved to opposite poles of the cell.

During which phase of mitosis do chromosomes decondense and new nuclei reform?

Telophase.

Cytokinesis in animal cells involves the formation of a contractile ring, leading to a _ division.

centripetal

How does cytokinesis occur in plant cells?

Vesicles form at the cell centre and fuse to create a cell plate, resulting in centrifugal division.

What is the primary purpose of meiosis?

To produce haploid sex cells (gametes) in reproductive organs.

How many cellular divisions occur in meiosis, and how many cells are formed?

Two divisions (Meiosis I and Meiosis II), resulting in four haploid cells.

Are the cells produced by meiosis genetically identical or different?

They are genetically different due to processes that create genetic variation.

What is the main purpose of mitosis in multicellular organisms?

Growth and repair of tissues.

Chromosome pairs, one from each parent, that have the same genes but potentially different alleles are called _ chromosomes.

homologous

The first meiotic division is known as a _ division because it separates homologous chromosomes and halves the chromosome number.

reduction

What is separated during the second meiotic division?

Sister chromatids.

What is crossing over and when does it occur?

The exchange of DNA segments between homologous chromosomes, occurring during Prophase I of meiosis.

The points where homologous chromosomes connect and exchange genetic material are called _.

chiasmata

What is random assortment in meiosis?

The random orientation and separation of homologous chromosome pairs at the equator during Metaphase I.

What is a karyogram?

A visual profile of an individual's chromosomes, organised in homologous pairs by descending size.

What is aneuploidy?

A condition where an organism has an abnormal number of chromosomes, such as one missing or one additional chromosome.

The failure of a chromosome pair to separate during anaphase of meiosis is called _.

non-disjunction

Down syndrome is an example of which type of aneuploidy, involving which chromosome?

Trisomy, involving an extra copy of chromosome 21.

What did the Hershey-Chase experiment use to label viral DNA and protein respectively?

Radioactive phosphorus (32P) for DNA and radioactive sulphur (35S) for protein.

What was the conclusion of the Hershey-Chase experiment?

It demonstrated that DNA, not protein, is the genetic material.

In a DNA nucleotide, the nitrogenous base always connects to the _-end of the pentose sugar.

1'

The two strands of a double-stranded DNA molecule are described as _ because they run in opposite directions.

antiparallel

What is the structural difference between purine and pyrimidine bases?

Purines (adenine, guanine) are double-ringed, while pyrimidines (cytosine, thymine) are single-ringed.

Why is a purine base always paired with a pyrimidine base in the DNA double helix?

To maintain a constant width and stability of the double helix.

What is a nucleosome?

The basic structural unit of DNA packaging in eukaryotes, consisting of DNA wrapped around a core of eight histone proteins.

Which enzyme reduces the torsional strain created by the unwinding of DNA during replication?

DNA gyrase.

What is the function of DNA primase in replication?

It generates a short RNA primer that acts as an attachment point for DNA polymerase III.

On which strand of the replication fork is DNA synthesised continuously?

The leading strand.

On the lagging strand, DNA is synthesised discontinuously in short segments called _.

Okazaki fragments

Which enzyme removes the RNA primers and replaces them with DNA nucleotides?

DNA polymerase I.

What is the role of DNA ligase in replication?

It joins the Okazaki fragments on the lagging strand to form a continuous DNA molecule.

What is the proofreading function of DNA polymerase III?

It can excise a wrongly added base using its 3' to 5' exonuclease activity before adding the next nucleotide.

What is a 'gene knockout'?

A technique for investigating gene function by making a specific gene inoperative within an organism.

What is the natural function of the CRISPR-Cas9 system in bacteria?

It provides immunity against viral infections by recognising and excising viral DNA from the bacterial genome.

In the CRISPR-Cas9 system, what is the role of the guide RNA (gRNA)?

It binds to the Cas9 nuclease and directs it to a complementary target DNA sequence.

How have scientists modified the CRISPR-Cas9 system for gene editing?

By using a synthetically derived gRNA to target any selected DNA sequence for removal or replacement.

What is a 'conserved sequence' in DNA?

A sequence that is identical or highly similar across all members of a species or a group of species.

What is a 'highly conserved sequence' in DNA?

A sequence that remains identical or highly similar over long periods of evolutionary time.

What is one hypothesis for why certain gene sequences are highly conserved?

The gene serves an essential functional requirement, and any mutation would likely prevent organism survival.

What is a second hypothesis to account for the presence of conserved sequences?

The gene is located in a region of the genome that has a slower rate of mutation.

Adenine and thymine are paired via hydrogen bonds, while guanine and cytosine are paired via hydrogen bonds.

two; three

The phase of the cell cycle where the cell grows, duplicates organelles, and replicates DNA is collectively known as _.

interphase

What term describes a cell that contains two sets of chromosomes, one from each parent?

Diploid (2n).

What term describes a cell, such as a gamete, that contains only one set of chromosomes?

Haploid (n).

Term: Kinetochore

A protein complex that attaches to the centromere of a chromosome and connects to microtubule spindle fibres.

What is the outcome of mitosis in terms of the daughter cells produced?

Two genetically identical diploid daughter cells (clones).

What is the main difference between anaphase I of meiosis and anaphase of mitosis?

In anaphase I, homologous chromosomes separate, while in anaphase of mitosis, sister chromatids separate.

How do single-stranded binding proteins (SSBPs) contribute to DNA replication?

They prevent the separated DNA strands from reannealing after helicase has unwound them.

DNA polymerase III synthesises a new DNA strand by adding nucleotides to the _-end of the growing chain.

3'