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Genetics
Genetics final
58
Medical
Graduate
12/09/2008

Additional Medical Flashcards

 


 

Cards

Term
Pleiotropy
Definition
A single gene affects multiple phenotypic traits. Thus, a new mutation in the gene will affect all the traits simultaneously
Term
Autosomal dominant - characteristics
Definition
Affects multiple generations,
males and females equally affected;
male-to-male transmission;
Offspring has 50% chance of being affected
Term
Di George syndrome
Definition

A.k.a velocardiofacial syndrome

Microdeletion on long arm of chromosome 22

(test by FISH)

May involve  issue with neural crest cell migration

Most often a de novo mutation

Term
Marfan syndrome
Definition

Autosomal dominant

 Long arms, fingers, toes, pidgeon breast, scolisis, myopia

Can lead to aortic dissection

Term
Huntington disease - mode of inheritance
Definition
Autosomal dominant
Term
Achondroplasia - mode of inheritance
Definition

Autosomal dominant

Most often is a new mutation

Term
Autosomal recessive - characteristics
Definition

Horizontal pattern of inheritance

Males and females equally affected

Both parents carry mutation --> 25% of being affected

Think consanguinity

 

 

Term
Cystic fibrosis - mode of inheritance
Definition
Autosomal recessive
Term
Sickle cell disease - mode of inheritance
Definition
Autosomal recessive
Term
X-linked recessive - characteristics
Definition

Incidence much higher in males and females

All daughters of affected males will be carriers

No male-to-male transmission

Sons of carrier females have 50% chance of being affected and 50% of being unaffected

Daughters of carrier females - 50% chance of being a carrier

Term
Hemophilia A - mode of inheritance
Definition
X-linked recessive
Term
Duchenne muscular dystrophy - mode of inheritance
Definition
X-linked recessive
Term
Mitochondrial inheritance
Definition

Inherited from mother only

Males and females are at risk of being affected

All daughters are at risk of transmitting the condition

Affected males cannot pass the condition to their children

Term

Heteroplasmy

(think mitochondria)

Definition

Mitochondria in a cell is heterogeneous for mtDNA that causes human disease

- deletion mutations that arise de novo are always heteroplasmic

Term

Homoplasmy

(think mitochondria)

Definition

All mitochondrial DNA in the organism is the same

Point mutations are generally homoplasmic and milder than deletions

Term
Leber hereditary optic atrophy - mode of inheritance
Definition
Mitochondrial
Term
Fragile X syndrome - characteristics
Definition

X-linked

Males are generally more severely affected than females

Full mutation - >200 repeats

Term
Anticipation
Definition

Trait appears either earlier or more severe in subsequent generations

Seen in Fragile X, Duchenne muscular dystrophy and Huntington disease

Term
Penetrance
Definition
How many people with the disorder actually show the disorder
Term
Expressivity
Definition
Multiple or variable manifestations are possible; different expressions of the same gene; may depend on other genes or environmental factors
Term
When does meiotic division begin for male gametes?
Definition
At puberty
Term
Metacentric chromosomes
Definition

Centromere is in the center

 

(Submetacentric - not quite in the center,

acrocentric - on one end)

Term
Genetic heterogeneity
Definition

Different genes can cause the same disorder

Example - osteogenesis imperfecta

Term
Aneuploidy
Definition
Errors in chromosome number
Term
Which monosomy is viable?
Definition
Turner syndrome - 45,X
Term
Which trisomies are seen clinically?
Definition

Trisomy 21 (Down syndrome)

Trisomy 13 (Patau syndrome)

Trisomy 18 (Edwards syndrome)

Term
Anaphase lag
Definition

One of the chromatids "lags" in meiosis; it is not incorporated into the nucleus of one of the daughter cells and is subsequently lost;

As a result, a mosaic is created - normal cells plus cells with monosomy

Term
Turner syndrome
Definition

45,X (a functional X chromosome is absent)

Symptoms - short stature; broad chest, low hairline, webbed nec; amenorrhea and infertility;

often congenital heart disease also present

Term
Robertsonian translocation
Definition

Between acrocentric chromosomes (13, 14, 15, 21, 22)

2 long arms join at centromere resulting in one giant chromosome; short arms are lost

 

6 possible gametes - 1 normal, 1 balanced, 2 monosomies, 3 trisomies

If identical chromosomes are translocated (21:21) - all gametes are unbalanced

 

 

Term
Wolf-Hirschhorn syndrome
Definition
4p- syndrome (deletion on 4p chromosome)
Term
Cri du chat syndrome
Definition

5p deletion syndrome

 

 Mental retardation, unusual facial features, behavioral problems

Term
Euchromatin
Definition
Loosely packaged, transcriptionally active; generally "housekeeping genes"
Term
Heterochromatin
Definition

Tightly packaged

Less transcription

Constituitive (telomeres, centromeres) and facultative (inactive X)  
Term
X inactivation
Definition

Random

XIST gene expressed by inactive X; product - large rRNA that coats inactive chromosome and changes it to heterochromatin

 Pseudoautosomal region - region that remain active; outside this region some genes also escape inactivation

Barr body - inactivated X in females

If some of the X chromosome translocated onto autosome and not inactivated - will have issues

Term
Imprinting
Definition

Imprinted genes are reset in gametes to reflect new parent of origin

 

Term
Uniparental disomy
Definition
Can be due to complementation, monosomic rescue, trisomic rescue, or mitotic error and rescue
Term
Angelman and Prader-Willi syndrome
Definition

Both due to imprinting issues in 15q11-q13

PWS - paternally imprinted genes not expresses

AS - maternally imprinted genes not expressed

 

Both cases - mostly due to deletion in that region; some have uniparental disomy; some have imprinting issues

 Test - karyotype with FISH (deletion), methylation-specific PCR (imprinting defects); DNA polymorphism testing (UPD)

Term
Karyotype testing
Definition

Look at chromosome number and gross chromosomal structure

Can be routine or high resolution

Term
Southern blot
Definition

Check for presence of sequence of interest; especially if too large for PCR

 

Good for looking for methylation differences

Term
FISH
Definition

Look for microscopic deletions or duplications

Use specific probes - so need to know what you're looking for.

Term
Comparative genomic hybridization (CGH)
Definition

Look for copy-number variants

Does not require prior knowledge of chromosomal location of any variant

Looks for submicroscopic deletions or duplications

Probes are in form of microarray

Competitive - add DNA of interest and DNA of a normal control, labeled with different fluorescent dyes and allow them to hybridize to probes in microarray

Term
DNA sequences
Definition

Looks at DNA sequence for specific mutations (point mutations, small deletions, insertions)

Does not detect large deletions

Term
Hardy Weinberg equilibrium
Definition

p + q = 1

 

p^2 + 2pq +q^2 = 1

 

When q^2 is rare,  p is close to 1 and thus heterozygotes are 2q

Term
AFP testing
Definition

Test maternal serum

 

Elevated AFP levels in neural wall defects (i.e. spina bifida) and abdominal wall defects

 

Decreased in Trisomy 18 and Trisomy 21

Term
SNP
Definition

Single nucleotide polymorphism

Polymorphic variation of a single nucleotide within a species

 

Term
Deformation
Definition
Mechanical forces disrupt normal structures
Term
Disruption
Definition
Actual destruction of previously normal tissue
Term
Dysplasia
Definition
Abnormal cellular organization of function within a specific tissue type
Term
Malformation
Definition
Failure or inadequate completion of one or more of the embryonic processes with early development of a particular tissue or organ system being arrested, delayed or misdirected
Term
Syndrome
Definition
Congenital abnormalities that occur in combinations that are more or less fixed giving a consistent pattern
Term
Maternal serum screening
Definition

Neural tube and abdominal wall defects (AFP)

Trisomy 21 and 18

 Cystic fibrosis

Spinal muscular atrophy

Ashkenazi Jews carrier panel

Term
Amniocentesis
Definition

13-23 weeks

AFP

Karyotype

Enzymatic studies (metabolic disorders)

DNA test

Term
Chorionic villus sampling
Definition

11-14 weeks

Karyotype

Enzymatic studies

DNA analysis

No AFP because no amniotic fluid

Can see placental mosaicism

Term
Osteogenesis imperfecta
Definition

Autosomal dominant

Often new mutation

Issues with collagen

Recognize by blue sclera (because it's very thin)

Many types

Term
Causes of bleeding
Definition

Hemophilia A and B

von Willebrand - very common; deficiency of factor required for platelet adhesion

Platelet disorders

Deficiencies in any clotting factors

Term
Hereditary hemorrhagic telangectasia
Definition

Dominant inheritance

Spontaneous bleeding

Arterial-venous malformations

Term
Locus heterogeneity
Definition
Phenotype can be caused by mutations at any one of several loci
Term
Allele heterogeneity
Definition
Phenotype can be caused by any of several mutations within a gene
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