Unrepaired doublestrand breaks will result in collapse of the DNA fork because the replication fork cannot continue beyond the area that has the doublestrand break. The other answers require the presence of at least one continuous strand of DNA.

The correct answer is abortive initiation. This is a normal transcription event is found in both prokaryotes and eukaryotes and occurs prior to promoter clearance, or the event when RNA polymerase escapes the promoter and begins elongation of synthesized transcripts. Abortive initiation is thought to occur when the RNA polymerase complex is not stable enough on the DNA. DNA scrunching describes the mechanism by which RNA polymerase transcribes, rather than RNA polymerase moving along DNA, it actually pulls DNA into the complex and unwinds it. 

The correct answer is Holliday junction. These intermediates in genetic recombination have symmetrical sequence and are mobile to preserve specific base pairing at recombination and damage loci. Repair enzymes recognize and subsequently localize to this DNA structure to facilitate locus specific enzymatic activity. 

A karyotype is produced by staining and photographing the chromosomes of a dividing cell. Pictures of the individual chromosomes are cut out and arranged in descending order of size. The chromosomes occur in homologous pairs that are similar in both staining patterns and size and have similar genetic material.

Physiological imaging is the visual representation of the functions of an organ, for example its blood flow, electrical activity, metabolism, and oxygen uptake. Radionuclide reflux imaging is a nuclear medicine scan used to determine whether an infant has gastroesophageal reflux. Phage type involves distinguishing subgroups of bacteria by the type of bacteriophage associated with that specific bacterium. Chromatography is the separation of two or more chemical compounds by their removal at different rates based on differential absorption and solubility. 

All of the given choices describe potential outcomes of chromosomal translocations. A translocation event occurs when recombination occurs between non-homologous chromosomes. The result is two chromosomes, each with genetic material from two different sets of genes that are generally kept separate.

Being present in a new environment may affect the expression of a gene (either an increase or decrease). Also, it is possible for translocations to occur in the middle of genes. The result of this could be newly formed non-functional (broken) genes or gene fusions between two coding regions that were originally separate. These alterations of gene expression have been implicated in many human diseases, including various cancers. 

Down syndrome is also referred to as trisomy 21. In about one in every 900 births, the child has an extra copy of the 21st chromosome.

Klinefelter syndrome is the result of a male being born with two X chromosomes and one Y chromosome. A deletion on the short arm of chromosome 5 causes Cri-Du-Chat syndrome; these children have respiratory problems and distinctive facial features. Williams syndrome is the result of genetic material missing from chromosome 7—in particular the gene for elastin, which causes disorders of the circulatory system and heart. A missing or incomplete X chromosome causes Turner syndrome. People who have Turner syndrome develop as females. 

About  newborns have a chromosomal abnormality, whether due to inheritance or as a result of meiotic events such as nondisjunction. 

Nearly half of all spontaneously aborted pregnancies are due to chromosomal abnormalities. This includes aneuploidy (an excess or loss of 1+ chromosomes), deletions (a loss of a piece of a chromosome), and translocations (the transfer of one chromosome piece to another).

DNA exists in the condensed chromatin form in order to fit into the nucleus. Negatively charged DNA loops twice around positively charged histone proteins to form a nucleosome bead. This nucleosome core is made up of two proteins each of histones H2A, H2B, H3 and H4.

H1 is the only histone protein that is not in the nucleosome core, and ties the nucleosome beads together in a string. H1 is located on the nucleosome exterior and help link DNA to the other proteins of the histone structure.

Telomeres are located at the ends of chromosomes and primarily serve the function of protecting the chromosome from degradation and fusion with neighboring chromosomes. The centromere is the site of attachment of two sister chromatids. Telomeres are not proteins; they are simply specialized portions of DNA. The sex chromosomes contain telomeres, but are only known as the sex chromosomes, allosomes, or chromosome 23.