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Flashcards in Definitions Deck (41)
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1
Q

The differential expression of genetic material depending on whether it was inherited from the male or female parent.

A

IMPRINTING

If a gene is maternally imprinted, the maternally-derived allele is inactive and only the paternal allele is expressed. If, on the other hand, a gene is paternally imprinted, only the maternal allele is expressed. For imprinted genes, the sex of the parent transmitting the disorder is important, not the sex of the affected offspring

eg Angelman syndrome, Prader Willi, Hydatiform mole, Beckwith Wiedemann syndrome

2
Q

The severity of some diseases increases as the disease is passed on through generations.

A

ANTICIPATION

Most commonly associated with expanded triplet-repeat mutations. The repeated sequence expands in successive generations, leading to a more abnormal phenotype.

eg Huntington’s disease, Fragile X, Spinocerebellar ataxia type 1, spinobulbar muscular atrophy

3
Q

Heterogenous expression of a disease at the cellular or tissue level, resulting from cell-specific differences in the expression of a mutation or the presence of a chromosome aberration.

A

MOSAICISM

Error in mitosis after fertilization and the initiation of development (termed postzygotic mosaicism). As a consequence, the affected individual is mosaic, with some cells carrying the mutation, while others do not.

As an example, a mutation occurring at the eight-cell stage would (theoretically) lead to one of eight cells in the body carrying the mutation. The expression of disease phenotype will then depend on which cell types harbour the pathogenic mutation.

4
Q

The proportion of persons carrying a pathogenic mutation who will manifest the disease, or the probability that a pathogenic mutation will result in disease.

A

PENETRANCE

5
Q

A substitution that changes a codon for an amino acid to a stop codon, leading to premature termination of translation of the mRNA transcript and a truncated protein. But lecture says NOT a truncated protein.

A

NONSENSE MUTATION

6
Q

A substitution that changes the codon for one amino acid to the codon for another amino acid. The composition and possibly the function of the protein does change.

A

MISSENSE MUTATION

7
Q

A change in one base that results in no change in the amino acid sequence of the protein, due to the redundancy of the genetic code (there is more than one codon for most amino acids)

A

SILENT MUTATION

8
Q

A substitution that alters binding affinities of transcript-related proteins, such as transcription factors, enhancers, silencers, or insulators. Such changes result in altered rates of transcription. Though protein structure is not altered by such noncoding variants, the level of transcript production can result in altered protein production, and in turn confer phenotypic variation.

A

REGULATORY POLYMORPHISM

9
Q

Autosomal recessive disease that derives from a single parent- duplication of one parent’s chromosome, other parent’s chromosome is supressed so affected individuals are homozygous for chromosome from one parent

A

UNIPARENTAL DISOMY

10
Q

Attachment of methyl groups to DNA at cysteine bases. Correlates with reduced transcription and is probably the principle mechanism in X chromosome inactivation and imprinting.

A

METHYLATION

Important in familial cancer genes eg BRCA1

11
Q

IVF increases risk of…

A

Beckwith Wiedeman syndrome

Angelman syndrome

12
Q

Mutations in different genes often cause the same disease

A

Locus heterogenicity

13
Q

Different mutations in a gene can cause different diseases

A

Allelic heterogenicity

eg mutation in TRPV4 causes three different conditions: metatropic dysplasia, AD brachydactyly and arhtropathy, hered sensorimotor neuropathy IIc

14
Q

The tendency for alleles of genes or genetic markers to be inherited in a non random fashion together

A

Linkage disequilibrium

15
Q

Concept of where substitution of the third nucleotide in the codon is less likely to alter amino acid substitution than substitution of the first or second

A

Degeneracy of genetic code

16
Q

How do you estimate carrier frequency?

A

Two times the square root of the incidence of disease

17
Q

Chromatin

A

Histones + double stranded DNA

18
Q

Chromatid

A

One of the two butterflies of the replicated chromosome. ie two chromatids joined by centromere. One copy of the duplicated chromosome.

19
Q

How many pairs of chromosomes?

A

22 pairs + one pair sex chromosomes.

20
Q

The 1-2% of the genome that codes for proteins?

A

The exome

21
Q

What is the order of the four phases of the cell cycle?

A

G1–>S (synthesis DNA)–>G2–>M

22
Q

What is non disjunciton?

A

Where aneuploidy results when gamete carries extra copy of a sex chromasome–>XXX or XO or XXY (OY not viable)

23
Q

Certain amino acids can be coded for by more than one codon.

A

Redundancy of the genetic code.

24
Q

What are the three possible outcomes of a missense mutation?

A

Loss function
Gain function
Protein misfolding

25
Q

Reduction by about half in the amount of protein, usually due to a whole gene deletion

A

Haploinsufficiency

26
Q

Alteration to the reading frame which may lead to an entirely different protein or stop codon

A

Frame shift.

27
Q

The position of a gene on a chromosome

A

Locus

28
Q

Alternative variations of a particular gene

A

Alleles

29
Q

There are at least two relatively common alleles in the population

A

Polymorphism

30
Q

Disease has penetrated, but looks different in different family

A

Expressivity

31
Q

Gain or loss of a whole chromosome

A

Aneuploidy

32
Q

Half the number of chromosomes that is normal

A

Haploid eg gametes

vs diploid in somatic cells

33
Q

Translocation between two acrocentric chromosomes (have almost no short arms)

A

Robertsonian translocation: basically just one tacked on to other, no actual loss of short arm as almost non existant

eg 14 and 21 join

Can then be “balanced” or “unbalanced” eg parent can be carrier for trisomy 21 if 21 is tacked onto 14 but they themselves only have one copy of normal 21. If have 2 copies of 21 and an extra on 17 it is unbalanced and will get Downs

Do the DOWNS kid’s karyotype first- if see chrom 14 involved then think about parent karyotype!

34
Q

In AR disorder, if both parents carriers, risk of getting disease?

A

25%

35
Q

AD pedigree- what features?

A

equal male and female affected
If see in each generation
Though remember that can have incomplete penetrance and seem to skip generation

36
Q

AR pedigree- what features?

A

Equal numbers males and females
Consanguinity may be present
Horizontal phenotype ie amongst a group of siblings pop up

37
Q

X linked recessive pedigree- what features?

A

No father to son transmission
Females rarely affected
(most X linked disorders are recessive)

38
Q

X linked dominant pedigree- what features?

A

females and males just as affected
often LETHAL in males, or survivors are mosaic
Males hemizygous rather than heterozygous
Females often have multiple miscarriages

eg x linked hypophophataemic rickets, incontinentia pigmenti

39
Q

Females have two x chromosomes but most genes on one copy not expressed

A

X-chromosome inactivation or Lyonisation

This means that if you have skewed X inactivation, can have different manifestations of a disease. ie girls with DMD

40
Q

Describe mitochondrial inheritance

A

Males and Females both affected
BUT only females can pass on
Also because of mosaicism, not every transmitting female will be affected necessarily

41
Q

RNA that does not code for a protein by mediates gene regulation process

A

non coding RNA (ncRNA)