Human Genetics

Genome

All genetic information contained in a cell.

Haploid cell

A cell that contains one complete set of chromosomes, approximately 3 billion base pairs.

Gene

The basic physical and functional unit of heredity that encodes for a protein or other product.

Karyotype

A picture of the chromosomes in an individual, arranged and classified.

Sister chromatids

Identical copies of a chromosome, joined together at the centromere.

Chromosomal abnormalities

Errors in chromosome number or structure which can result in genetic disorders.

Polyploidy

A condition where a cell has extra whole sets of chromosomes.

Aneuploidy

A condition of having an abnormal number of chromosomes, usually due to non-disjunction.

Translocation

The transfer of a chromosome segment to a non-homologous chromosome.

Mosaicism

A condition where two or more genetically different cell lines exist in a single individual. Comes form x-inactivation, or non-disjunction in mitosis somatic mutation

Independent assortment

The process by which different genes independently separate from one another when reproductive cells develop.

Meiosis

A type of cell division that reduces the chromosome number by half, resulting in the formation of gametes.

Autosomal recessive inheritance

A pattern where two copies of an abnormal gene must be present for the disease or trait to develop.

Barr bodies

Inactivated X chromosomes in females, typically one per female cell.

X-linked inheritance

A pattern of inheritance in which a gene is located on the X chromosome.

Mitochondrial inheritance

Genetic transmission through mitochondria, typically maternal, affecting all offspring.

Gene flow

The transfer of genetic variation from one population to another.

Microsatellites

Short, repetitive sequences of DNA that are highly variable and used as genetic markers.

Acrocentric chromosomes

Centromere toward the end of the chromosomes. Includes 13, 14, 15, 21, and 22

Mixoploidy

Two or more cell lineages mixed (mosaicism or chimerism)

Reciprocal translocation

Nothing is lost or gained as long as the breakpoint doesn’t disrupt function. Produces 2 complete chromosomes, they just don’t look how they’re supposed to

FiSH

Good for quick chromosome count and detection of known/suspected deletionsand duplications in specific regions.

Microarray analysis

A way to measure the quantity of a given sequence of DNA in a sample. Used to detect full or partial aneuploidy. Doesn’t work on translocation

Downs syndrome

Trisomy 21

Edward syndrome

Trisomy 18, partial or mosaic form may be milder

Turner syndrome

Monosomy X

Klinefelter syndrome

XXY syndrome

Translocation carrier

An individual who carrier a balanced chromosome translocation. Phenotypically normal, but have a high risk of miscarrying

Inherited translocation

Translocation carriers may pass the balanced (or unbalanced) form of a translocation onto their offspring

Autosomal reciprocal translocation

Exchange of segments between two non-homologous autosomal chromosomes. Balanced carriers are usually unaffected

Robertsonian translocation

Fusion of the long arms of two acrocentric chromosomes, the short arms are lost

Heterologous robertsonian

A robertsonian caused by the fusion of the q arms of two different acrocentric chromosomes

Homologous robertsonian

A robertsonian caused by the fusion of the q arms of two copies of the same chromosome

Autosomal recessive

Usually only one generation affected. Children of carriers at 25% risk, unaffected children have 66% chance of being a carrier. Includes cystic fibrosis and sickle cell anemia

Autosomal dominant

Affects multiple successive generations. Children of affected individuals are at 50% risk. Includes Huntington’s disease and Treacher Collins

X-linked

Multiple generations affected. Males more severely affected. All daughters of affected males will be carriers/affected. Includes hemophilia and red-green colorblindness

X-linked mosaicism

Which X (Maternal or paternal copy) is chosed for inactivation in an XX embryo is determined randomly and independently by each cell of the embryo. Once a cell has chosen which X to inactivate, that X remains inactive in all its daughter cells. Mosaicism makes it so that women will dometimes express diseased X

Y-linked

Only present in males, super rare. Includes spermatogenic failure

Mitochondrial inheritance

All children of an affected female will be affected. Significant variation in severity, but tends to get worse with each generation. Includes mitochondrial myopathy

Gonadal mosaicism

When the gamete population of an individual is mosaic for an allele. Can cause unaffected individual to have multiple children with an autosomal dominant condition

Chimerism

Mosaicism tha tis the result of an absorbed twin, bone marrow transplants, or it happens in pregnant women

Locus heterigeneuty

Same clinical phenotype from mutations at any one of several different loci

Allelic heterogeneity

Different mutations at the same locus result in the same clinical phenotype

Syndrome

A well-known pattern of anomalies beieved to have the same cause, often genetic/chromosomal but may be environmental. Ex: Achondroplasia (dwarfism)

Sequence

A group of related anomalies believed to be caused by a single major anomaly that alters the development of other structures. Ex: Oligohydramnios sequence (potters sequence)

Zellweger syndrome

Autosomal recessive disease caused by errors in peroxin genes (peroxisomes)

Epidermis bullosa

Extreme skin fragility