LINE (L stands for long) is a small piece of foreign DNA that have been inserted into the chromosomes of a multicelled organism by foreign agents such as retroviruses. LINEs include an open reading frame for reverse transcriptase.

There is an increased twin concordance, suggestive of a genetic contribution, but since twins are not fully concordant, other non-genetic factors must also be involved.

The threshold model postulates that the phenotype is absent until a threshold of liability is reached, after which the phenotype is expressed.

Here the chromosomes condense to form tetrads and exchange DNA. The nucleolus and nuclear envelope disappear. Homologous chromosomes pair in prophase I.

Phytohemagglutinin stimulates the division of T-cells. A mitotic arresting drug such as colchicine is used to collect dividing cells at metaphase and hypotonic treatment swells the cells to permit chromosomes to be visualized.

Trisomy 13 is also known as Patau syndrome. It is a genetic disorder in which an individual has three copies of genetic material from chromosome 13, instead of the usual two copies.

Alpha satellite is a specific form of highly repeated DNA, which is concentrated at centromeres.

Since females are more often affected, having an affected son implies greater liability towards the trait. This increases their risk for future offspring. The trait will always be more common in females than males.

G-light bands, for the most part, exhibit dull quinacrine fluorescence.

If two copies of chromosome 21 have the same maternal alleles, the nondisjunction must have occurred in maternal meiosis II, when the two identical chromatids normally separate.

Having maternal uniparental disomy for chromosome 15 results in Prader-Willi syndrome. It is caused by the loss of function of genes in a particular region of chromosome 15 & affects many parts of the body.

Only advanced maternal age has been conclusively shown to be associated with nondisjunction.

The Hardy-Weinberg equilibrium applies to systems with two or more alleles.

Genetic drift is the random fluctuation of allele frequencies that can occur in a small population.

A balanced polymorphism occurs when homozygotes are selected relative to heterozygotes.

Extinction of a lethal allele can be prevented by replacement of lost alleles due to new mutation.

The founder effect occurs when a population bottleneck occurs leading to an effective increase in the frequency of a previously rare allele.

If there is true random mating in the new population, equilibrium will be achieved in one generation.

The t(9;22), also called the Philadelphia chromosome, is a characteristic of chronic myelogenous leukemia.

Tumor suppressor gene mutations are transmitted in a dominant manner in families, but act recessively in tumor cells,which is why two hits are required in the tumor.

It is a normal gene that can become an oncogene due to mutations or increased expression. They are derived from RNA tumor viruses.

It is the first stage of mitosis, during which the chromosomes condense and become visible. The nuclear membrane breaks down & the chromosomes condense during prophase.

Double minute chromatin bodies are indicative of gene amplification, one of the mechanisms of oncogene activation.

Due to mutation in one of several genes, HNPCC is involved in DNA mismatch repair.

The father's allele would be preserved in the tumor. This is a mutant allele, based on the fact that the father has retinoblastoma.