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A procedure done at 14-16 weeks gestation where amniotic fluid is sampled via a long needle inserted through the abdominal wall. Fetal cells from this fluid are obtained and examined for abnormalities. This technique can detect chromosomal disorders such as Down syndrome.


An abnormal number of chromosomes present in a fetus. The number can be either too many or too few. These abnormalities are usually fatal in the early first trimester except for trisomy of chromosomes 21, 18, and 13 or the sex chromosomes. Infants with trisomy of 18 and 13 usually die within the first year of life.


A human embryo 5-8 days after fertilization is called a blastocyst. It is a hollow ball of approximately 100-250 cells, which contains an inner cell mass that differentiates into the fetus, and an outer layer of cells that forms the placenta. It is at the blastocyst stage that the embryo implants into the uterus.

Cell free fetal DNA testing

This test is an alternative to invasive pre-natal diagnostics such as amniocentesis that provides non-invasive testing to determine gender of the fetus. There is also promising research that is using cell free testing to detect trisomy 21.

Chorionic villus sampling

A procedure done at 10-12 weeks gestation which involves sampling of the placenta via a needle inserted through either the cervix or the abdominal wall. It carries a 0.5-1% risk of miscarriage.

Chromosomal nondisjunction

The failure of chromosomes to properly separate during meiosis. This causes the daughter cells to have imbalanced chromosomes; such cells are referred to as aneuploid cells.


Freezing of embryos for storage and return with maintenance of viability.

DNA microarrays (gene chips)

A glass or silicon chip with a large collection of microscopic spots of different DNA molecules attached to it. These chips may be used to investigate gene expression or analyze single nucleotide polymorphisms.

Down syndrome

Trisomy (three copies) of chromosome 21, which causes abnormal features, mental retardation, and cardiac malformations, among other problems.

Exome sequencing

A strategy to selectively sequence the coding regions (exons) of a genome. This technique is a cheaper alternative to whole genome sequencing, however it does not provide information about non-coding DNA, which has been implicated in essential regulatory functions.

First trimester of pregnancy

Weeks 2-12 of pregnancy, the time during which most miscarriages occurs.

Genetic screening

Detection of genetic diseases before signs and symptoms occur.

Genome-wide association study (GWAS)

Studies that compare DNA of people with a disease to DNA from people without a disease to determine which differences in DNA are associated with the disease. These are most commonly done via single nucleotide polymorphism (SNP) analysis.

Haplotype mapping

This technique utilizes haplotypes (groups of alleles that tend to be inherited together) combined with SNP analysis to trace these haplotypes, to map heritability of disease genes. As in GWAS, DNA is compared between affected and unaffected individuals, however fewer SNPs need to be analyzed in haplotype mapping, as many SNPs fall within each haplotype.


Studies/procedures occurring artificially outside of the human body.

In vivo

Studies/procedures occurring naturally inside the human body.

Incidence of disease

The risk of developing a disease within a specific period of time, usually expressed as a proportion or rate. Not to be confused with prevalence, which is the number of people in a given population with the disease.


In vitro fertilization or fertilization occurring in a laboratory.

In vivo fertilization

Fertilization occurring in a woman’s body in her reproductive organs.

Mendelian inheritance

Traits whose heritability may be linked to one gene that exhibits traditional autosomal dominant or autosomal recessive inheritance. Medelian statistical measure cans be applied to genetic traits of this nature to calculate risk percentages for expression of the disease.

Autosomal dominant inheritance

One copy of a disease-causing gene is required for disease phenotype to occur. If either parent has the disease, the offspring has a 50% chance of being affected.

Autosomal recessive inheritance

Two copies of a disease-causing gene are required for disease phenotype to occur. Both parents need to either be carriers for the disease or be affected by the disease in order to produce offspring with the disease.


The medical subfield that specializes in preserving the fertility of cancer patients after treatment.


The technical term for the unfertilized female egg that is released at ovulation. All normal oocytes have a 23,X genotype.


Pertaining to more than one gene. Polygenic traits do not follow patterns of Mendelian inheritance but rather their phenotypes exhibit a continuum along a normal distribution (Bell curve). Risk factors for expression of polygenic diseases can be characterized through published disease-specific studies.

Pre-implantation testing

Genetic testing performed on an oocyte or fertilized egg before it implants in the uterus.

Pre-natal ultrasound testing

Ultrasound scans (also known as sonograms) are an important noninvasive test to assess fetal development. A fetal heartbeat is usually visible at 7 weeks, while gender may be determined accurately at 13 weeks. Ultrasound is a useful tool in detecting abnormalities in the developing fetus such as abnormal nuchal translucency seen in Down syndrome.

Prevalence of disease

The total number of cases of a disease in the population at a given time, counting both newly diagnosed and chronic cases. Not to be confused with incidence, which is the number of new cases of disease in a specific time period.

Proteomic analysis

The proteome is the total population of proteins produced by an organism or system at a given point in time. This will vary as the organism ages or is exposed to different conditions or stresses. Proteomic analysis seeks to capture and catalog these differing populations of proteins in multiple cell types and states. For example, there has been extensive research on the proteomics of cancer cells.