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Flashcards in Definitions Deck (18):

Define Hypomorphic

Phenotype with partial wild-type activity.
Hypomorph = an allele that produces a reduced amount or activity of a product


Define Sex-limiting

Sex-limited genes are genes which are present in both sexes but expressed only in one sex. Causes the two sexes to show different traits or phenotypes.
Examples: lactation in females and beard growth in males.


Define Haploinsufficiency:

A situation in which half amount of a gene product is not enough to maintain normal function for instance, individual with heterozygous mutation or Hemizygous at a particular locus is clinically affected.


Define variable expressivity

Variable extent or intensity of phenotypic signs among people with a given genotype


Define penetrance

Refers to the proportion of people with a particular genetic change who exhibit signs and symptoms of a genetic disorder. If some people with the mutation do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.


Define compound heterozygous

The presence of two different mutant alleles at a particular gene locus, one on each chromosome of a pair. These 2 mutations are different and not identical to each other (identical mutations on both alleles called Homozygous).


Define age related mosaicism

The accumulation of somatic/germline mutations over the course of a person’s life resulting in mosaicism. Normal part of ageing considering number of cells dividing and mutation rate of DNA.


Define hemizygous

a state of having a gene with no counterpart allele in a diploid cell. E.g. men are normally hemizygous for genes on the X chromosome.


Define UPD

When there's 2 copies of a chromosome/region of chromosome received from one parent
Types of UPD
Uniparental isodisomy (UPID) (likely MII NDJ / mitotic error)
Uniparental heterodisomy (UPHD) (likely MI NDJ)
** can have segmental UPID & UPHD on 1 chrom due to recombination


Define Anticipation
Name 2 syndromes that have this

Phenomenon in which the age of onset of a disorder is reduced
and/or the severity of the phenotype is increased in successive generations. typically occurs with disorders that are caused by an unusual type of mutation called a trinucleotide repeat expansion.

Huntingtons disease
Myotonic dystrophy
?fragile x (controversial)


Define imprinting

An epigenetic phenomenon that leads to parent- specific expression of a subset of genes between alleles


Define mosaicism

The presence of two or more genetically different cell lines with in one individual that have arisen in a single zygote


Define homozygous

When both alleles in a diploid organism are the same eg aa, AA, BB, bb


Define heterozygous

When two alleles in a diploid organism are different eg aA, bB


Define autozygosity

Termed identity by descent. IDB
Where homozygous alleles are both inherited from a common ancestor.
(Similar to UPID but it's not a meiotic error- it's due to consanguinity)


Define paralogous

2 distinct non-allelic regions of DNA with highly similar DNA sequences


Define clinical utility

The benefit to the patient the test/ results will be


Define clinical validity in terms of a test for a patient

The results of the test will be of clinical significance