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Genetic Diseases > Terms > Flashcards

Terms Flashcards

1
Q

Genetic Drift

A

Isolated population will change with time, due to pressures and random events

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2
Q

Gene Flow

A

Intermixing of populations, from small numbers or large migrations adds new alleles, brings in mutations

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3
Q

Founder Effect

A

very few founders, may mean gene frequencies do not reflect larger popluation

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4
Q

Segregation

A

Two copies of each gene are in the parent but the offspring will receive one. There is an equal probability to inherit either one of those copies

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5
Q

Independent Assortment

A

Each gene is inherited independently of the other genes. Genes affecting the same function are not not inherited as a group.
The exception occurs in cross-linking

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6
Q

Multiplication rule

A

Probablility of multiple events occurring together. Multiply the risks of each event to get overall risk

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7
Q

Addition rule

A

Probability of either one or another of multiple events occurring. Add risks of each to get overall risk. All add up to one.

Example, Probability of having three kids and of those three having at least on boy and one girl. 1/8 all girls and 1/8 having all boys = 3/4 chance of that not occurring.

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8
Q

Autosomal Dominant

A

Single copy of the gene can cause the phenotype.

Usually half of children will be affected (50% recurrence risk). Father-Son transmission rules out x-linked.
No-skipped generations (a positive phenotype has to be present to pass down trait)

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9
Q

Autosomal Recessive

A

Disorders are rare individually generally as two parents have to be carriers (Aa x Aa). Recurrence risk is 25% with two carrier parents.

Possible to skip a generation. Males and females are equally as likely which rules out sex-linked pattern

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10
Q

New Mutation

A

Occurs when the inheritance pattern shows no other affected individuals when they would be likely as in autosomal dominant or x-linked
Parentage of child is confirmed
and Neither parent has evidence of carrying the mutation.

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11
Q

Germline Mosiacism

A

Mutations occur in one of many cells that produce many or few germ cells. As a result Autosomal dominants or X-linked disorders appear in very unlikely pedigress or odd proportions.

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12
Q

Reduced Penetrance

A

Phenotype mild to non-existing in some individuals due to modifying genes. May affect children more severely.

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13
Q

Age-dependent Penetrance

A

Combination of delayed age of onset and reduced

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14
Q

Variable expression

A

Severity of disorder depends on expression. One child may have 3 out of the 5 different anomalies associated while another child may have all five.

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15
Q

Pleiotrophy

A

Multiple effects from one mutation. The single mutated gene can affect multiple tissues.
DNA transcription factors and extracellular matrix proteins.

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16
Q

Alellic heterogeneity

A

Multiple mutant forms causing different effects of the same gene. Example is the gene that codes for hemoglobin. Mutation causes hemoglobin disorders, sickle cell and B-thalassemias.

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17
Q

Locus Heterogeneity

A

Multiple genes affect one pathway and a similar disorder can be produce but different genes may be affects. Urea cycle defects all cause mental retardation

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18
Q

Anticipation

A

Some disorders are more severe in later generations (such as myotonic dystrophy) or they may occur earlier (E.g Huntington’s disease).

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19
Q

Repeat expansions

A

Short sequence of direct repeats in gene. Some are repeated codons (E.g. CAGs in Huntington’s disease).

In Meiosis repeats get longer

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20
Q

Proband

A

A particular subject being studied or reported on. Denoted with an arrow on a pedigree.

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21
Q

Consanguinity

A

Marrying and having children with a blood relative (someone of the same kinship).

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22
Q

Coefficient of Relationship

A

The porbability of sharing a common gene from an ancestor.

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23
Q

X-linked Recessive

A

Passed through the female line, appear mostly as affected males if they do not reproduce. Affected females will have all affected boys.
No father-son transmission. Passage through females can give “skipped generations”

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24
Q

X-Linked Dominant

A

More females will be affected. In all generations. No father son transmission. All Daughters of affected males are affected.

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25
Q

Dosage Compensation

A

Females have two X chromosomes. One of the two need to be turned off (X-inactivation) to prevent the appropriate amount of gene expression

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26
Q

Barr Body

A

Inactivated X chromosome. Inactivation is random (half cells have one X and the other have the other X), fixed (All descendants have the same X inactivated), and incomplete (A few genes escape inactivation; may have counterparts on Y)

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27
Q

Vertical Transmission

A

Seen in every generation

28
Q

Y-Chromosome Inheritance

A

Holandric inheritance
Strictly father-son.

Y Chromosome has genes that are involved in sex determination, spermatogenesis and testicular function.

Have homologues on the X chromosome all in one region that escapes inactivation. X-Y crossing over can occur in this region.

29
Q

Mitochondrial Inheritance

A

Inheritance is strictly maternal for mitochondrial inheritance. Mutation rate is high in the kidney because of lack of repair systems and lots of free radicals from oxidative metabolism.

Condition related to variable expression. Percentage of mutant molecules determines status of mitochondrial function.

30
Q

Heteroplasmy

A

Mutation in mictochondria may be present only in some cells.

31
Q

Sherman Paradox

A

Normal transmitting males occur but not affected, but have affected descendants. The mothers of transmitting males have less affected daughters than the daughters of transmitting males. Daughters of normal transmitting males are never affected but their children may be

32
Q

Imprinting

A

Genes modified during gametogenesis, which controls the function of those chromosomes in offspring.

33
Q

Centimorgans

A

The percent of the chromosomes the recombine between two genes. Really a measurement of how close two genes are to one another. 1 cM = 1% of the chromosomes recombine between two genes.

34
Q

Linkage Phase

A

Arrangement of alleles on each chromosome.

Can be used to follow a gene in a family. Geneticists can trace the inheritance of a linked marker rather than mutation which is helpful if the area of the gene is unknown but the linked marker is.

35
Q

LOD score

A

Logarithm of odds

The LOD score compares the likelihood of obtaining the test data if the two loci are indeed linked, to the likelihood of observing the same data purely by chance

Used to calculate the likelihood that observed data fits a given hypothesis and compare that to the likelihood gene are unlinked. This creates a likelihood ratio or the “odds” genes are linked

Values of 3 or above is significant for linkage (1000x greater for linkage). Value of -2 suggest no linkage (100x less likely for linkage)

36
Q

Polymorphism

A

When two or more phenotypes clearly exist

Required for a marker in gene mapping to be polymorphic. Markers in microsatellites have advantages of being highly polymorphic, scatter throughout the genome and easy to screen

37
Q

Uninformative mating

A

Some combinations do not give enough information to determine linkage phase. Can be because same marker allele on both chromosomes or cannot follow through subsequent generation.

38
Q

Linkage Disequilibrium

A

A mutant gene more likely to carry a specific allele at linked marker. With time, recombination will separate mutation from marker. Can give a rough estimate of mutation’s age

39
Q

Linkage equilibrium

A

Initially a mutation will only be associated with certain markers. Through time recombinants occur between chromosomes. Eventually equilibrium will look like the normal population

40
Q

Association

A

When a specific allele significantly increases the risk a person is affected but there is no known linkage

41
Q

Genome Wide Association Studies

A

GWAS is used to locate genes. Many markers are screened in one test. Can screen many markers such as Single nucleotide polymorphisms

42
Q

Chromosome Anomalies for mapping genes

A

Changes to chromosome are useful. Series of deletions allow small common region to be identified. Translocation breakpoints may be in a specific gene

43
Q

Caenorhabditis elegans

A

nematode
Short generation, complete cell fate map
Alternate body plan, not a vertebrate

44
Q

Drosophila melanogaster

A

fruit fly
Short generation, easy to breed, lots of mutants
Alternate body plan, must maintain live stock

45
Q

Danio rerio

A

zebrafish
Transparent embryos, easy to breed
Small embryo difficult to manipulate

46
Q

Xenopus laevis

A

Clawed frog

Large transparent embryo, can manipulate easily
Tetraploid, makes genetics difficult

47
Q

Gallus Gallus

A

Chicken

48
Q

Mus Musculus

A

Mouse

49
Q

Three types of genetic mediators in development

A

Paracrine signalling
DNA transcription factors
Extracellular matrix proteins

50
Q

Four major families of paracrine molecules

A
  • Fibroblast Growth Factor (FGF)
  • Hedgehog proteins
  • Wingless family (Wnt)
  • Transforming Growth Factor-B (TGF-B)
51
Q

FBFR3 Mutation

A

FGF receptors
3 Ig-like domains, Transmembrane domain, and split kinase domain

Expressed in growing bones. Mutations cause skeletal dysplasias

Autosomal dominant FGFR3 mutation

52
Q

Three families of Transcription factors

A

Homeobox - HOX, PAX, EMX, MSX
High-mobility group (HMG) - SOX family
T-box family - TBX

53
Q

SOX Family Transcription factor

A

Sry - sex-determining region of Y. Regulates SOX9 expression in genital ridge and chondrogenesis and Col2A1. Mutation causes camptomelic dysplasia. Short limbs, sex-reversal of XY fetuses

54
Q

Extracellular matrix proteins

A

Important in development that create the scaffold for tissues. Collagens, fibrillins, elastins, laminins, fibronectins, tenascins. Cells bind using integrins and glycosyltransferases

55
Q

Sonic Hedgehog

A

Involved in neural tube, somites, limbs and left-right axis in deleopment. Defects disrupt midline brain development. Holoprosencephaly is severe form. Severe mental retardation and early death.

56
Q

HOX gene expression

A

Four patterns of similar genes but on different chromosomes. HOXA, HOXB, HOXC, HOXD. Up to 13 genes but only 39 total.

Paralogs are genes in same relative position

57
Q

Temporal colinearity

A

3’ genes are expressed earlier (i.e HOXA1 is expressed before HOXA2

58
Q

Spatial colinearity

A

3’ genes expressed more anteriorly

59
Q

Homeotic Transformation

A

Missing gene in Hox gene expression means segment identity wrong. Segment transforms incorrectly

60
Q

Noggin, Chordin and Bmp4

A

Noggin and Chordin bind Bmp3 to prevent it from binding to receptor. Bmp4 is a ventralizing signal so when inhibited by Noggina and Chordin the segement becomes posterior

61
Q

Left/Right Axis defect

A

Asymmetrical expression of SHH. Causing the left side expression of nodal (TGFB).

Mutation in dynein which decreases motor protein in cilia which is why situs inversus patients have increased risk to upper respiratory tract infections.

62
Q

ZIC3

A

Zinc-finger protein of the cerebellum. Gli transcription factor family, X chromosome. Affects males with randomization defects. Heterozygote females have L/R reversal.

63
Q

FGF8

A

A candidate for inductive signal. signal mediated by Fgf10 expression in mesoderm. Wnt2b and Wnt8c maintain Fgf10 expression.

FGF8 loss shows a lack of development of the AER (apical ectodermal ridge). The ZPA (Zone of Polarizing activity) uses SHH to maintain the AER. AER is essential for dorsal/ventral and left/right axis

64
Q

IPF1

A

gene for development of the pancreas B-cells to express insulin. IPF1 mutations block pancreatic development. Meaning that IPF1 gene not only regulates insulin but also pancreatic cell maturation and differentiation

65
Q

Knudson’s Two-Hit model

A

Retiboblastoma bilateral, runs in families and unilateral appears sporadically. In a familial or bilateral, offspring are increased risk and a mutation in the remaining good copy causes mutation in cells.

66
Q

Cancer Inheritance Paradox

A

Mutations show a dominant inheritance pattern in pedigrees. Recessive at cellular level because a second mutant copy is required to have complete loss of function of that gene.

67
Q

Loss of Heterozygosity

A

Heterozygous loci are studied for genetic mapping of cancer genes. Lost markers indicate loss of heterozygosity near gene of interest. Comparing normal cells in tumor cells in which the tumor cell has lost a marker indicate loss of heterozygosity. This gives the probability of the gene being located on that chromosome

Genetic Diseases (2 decks)

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