Definitions

Question 1

Define Hypomorphic

Answer 1

Phenotype with partial wild-type activity.

Hypomorph = an allele that produces a reduced amount or activity of a product

Question 2

Define Sex-limiting

Answer 2

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.

Question 3

Define Haploinsufficiency:

Answer 3

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.

Question 4

Define variable expressivity

Answer 4

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

Question 5

Define penetrance

Answer 5

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.

Question 6

Define compound heterozygous

Answer 6

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).

Question 7

Define age related mosaicism

Answer 7

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.

Question 8

Define hemizygous

Answer 8

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.

Question 9

Define UPD

Answer 9

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

Question 10

Define Anticipation

Name 2 syndromes that have this

Answer 10

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)

Question 11

Define imprinting

Answer 11

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

Question 12

Define mosaicism

Answer 12

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

Question 13

Define homozygous

Answer 13

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

Question 14

Define heterozygous

Answer 14

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

Question 15

Define autozygosity

Answer 15

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)

Question 16

Define paralogous

Answer 16

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

Question 17

Define clinical utility

Answer 17

The benefit to the patient the test/ results will be

Question 18

Define clinical validity in terms of a test for a patient

Answer 18

The results of the test will be of clinical significance