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FMS > [FMS] MCG - genetics and inheritance > Flashcards

[FMS] MCG - genetics and inheritance Flashcards

1
Q

what is a genotype

A

full complement of all the genes in the genome

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2
Q

what is a phenotype

A

the functional consequence of a gene (or combination of genes)

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3
Q

what is a monogenic disorder, give an example of a monogenic disorder

A

disorders associated with single gene
e.g. cystic fibrosis

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4
Q

what is a polygenic disorder, give an example of a polygenic disorder

A

disorders associated with many different genes
e.g. Type II diabetes

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5
Q

what is chromatin?

A

DNA + histones = chromatin

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6
Q

how is DNA ‘packaged’

A

DNA is packaged in the nucleus in conjunction with positively charged histone proteins

DNA + histones = chromatin

Octamer of histones 2x (H2A, H2B, H3, H4) forms a core with the DNA around the outside

Histone octamer = nucleosome

H1 links nucleosome together

Nucleosomes form a chromatin fibre

Chromatin fibre loops out of a central nuclear matrix protein that create the individual chromosomes

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7
Q

out of the 23 pairs of chromosmes, how many are autosomes and how many are sex chromosomes

A

22 pairs of autosomes
1 pair of sex chromosomes

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8
Q

what are chromosomes stained with and where

A

stained at metaphase with giemsa dye

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9
Q

what is cytogenics?

A

the study of the genetic component of a cell through the visualisation and analysis of chromosomes

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10
Q

which chromsome is the largest and which is the smallest?

A

Chromosome 1 is largest and chromosome 22 is the smallest

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11
Q

what is the normal female karyotype and male karyotype?

A

Normal female karyotype is 46 XX
Normal male karyotype is 46 XY

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12
Q

describe the chromosome arms?

A

short (p)
^ hehe short peepee

long (q)

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13
Q

how can the location of genes be specified?

A

based on the G-banding pattern and the arm of the chromosome

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14
Q

how does the body prevent female cells from having double the amount of X-linked genes

A

X-chromosome dosage compensation - Female cells are 46 XX however only one of the X chromosome is active

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15
Q

how is one of the X-chromsomes inactivated in x-chromosomes dosage compensation?

A

Early in embryology one of the X chromosomes inactivated randomly

A gene on the X-chromosome is transcribed as Xist ncRNA – this RNA triggers the transcriptional silencing of one of the X-chromosomes

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16
Q

what region of Y is required for male development?

A

SRY gene

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17
Q

what protein is encoded by the SRY gene?

A

testis-determining factor (TDF)

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18
Q

what is euploidy?

A

normal number of chromosomes

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19
Q

what is aneuploidy

A

irregular number of chromosomes

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20
Q

what is aneuploidy caused by?

A

the failure of homologous chromosomes to separate properly during meiosis = non-disjunction

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21
Q

which trisomies lead to live births?

A

13, 18, 21

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22
Q

what is trisomy 13?

A

patau syndrome

47 XX +13 or 47 XY +13

Common abnormalities:
include heart defects
incomplete brain development

mean survival ~130 days

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23
Q

what is trisomy 18?

A

Edward’s syndrome

47 XX +18 or 47 XY +18

Very rare live birth (95% die in utero) numerous

abnormalities: heart and intestinal development

10% survive for 12 months

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24
Q

what is trisomy 21?

A

Down syndrome

47 XX +21 or 47 XY +21

abnormalities:
growth and development delay
cardiac abnormalities
increased risk of acute leukaemia

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25
Q

which trisomy is downs syndrome

A

trisomy 21

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26
Q

which trismoy is pataus syndrome

A

trisomy 13

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27
Q

which trisomy is edwards syndrome

A

trisomy 18

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28
Q

when is amniocentesis carried out?

A

during weeks 15-20 of pregnancy

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29
Q

how do you check for chromosomal abnormalities?

A

Amniocentesis

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30
Q

when does the majority(95%) of non-disjunction occur?

A

during oogenesis

^ Spermatogenesis continues throughout life after puberty

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31
Q

how can you tell a disease is autosomal recessive from a pedigree?

A

Trait is rare in pedigree

Trait often skips a generation

32
Q

in autosomal recessive diseases which sex is affected more?

A

neither, affects both

33
Q

do the parents of affected individuals with autosomal recessive diseases have the disease?

A

no - Parents of affected individuals do not have the disease

34
Q

give an example of an autosmal recessive disease?

A

CF

35
Q

what is CF caused by?

A

mutation of the Cystic fibrosis transmembrane conductance regulator (CFTR) gene

most common is CFTRD508 (deletion of codon 508)

36
Q

what is a normal, functional allele called?

A

wild type allele

37
Q

can you give a biological explanation as to how CF is recessively inherited? why carriers are unaffected?

A

CFTR pumps Cl- out of cells and leads to water exiting the cell by osmosis
Normally 50% of the CFTR is produced from the paternal allele and 50% from the material allele
When an individual inherits a single mutant allele the cell only produces 50% of the normal amount of CFTR
This 50% is sufficient to provide the function that is needed in the cell
It is also possible there is upregulation of the normal allele to compensate

38
Q

biologically explain what happens when an individual has CF

A

the mutant CFTR does NOT exit the endoplasmic reticulum as usual = loss of cl- = thicker mucus

39
Q

how can you tell a disease is autosomal dominant in a pedigree?

A

Trait is frequent in pedigree

Individuals are affected in each generation.

40
Q

are males and females affected equally or unequally in an autosomal dominant pedigree?

A

Trait affects males and females equally

Trait is transmitted by either sex

41
Q

in an autosomal dominant pedigree do the parents have the phenotype?

A

yes

42
Q

give an example of an autosomal dominant disease?

A

Huntington’s disease (HD)

43
Q

what is huntingtons caused by

A

Caused by mutations at HD locus

Mutant HD gene has MORE THAN 36 repeats of CAG sequence instead of ~28

44
Q

biologically explain how someone has HD

A

A patient who is a heterozygote with a single mutant allele (Hh) develops the disease

Mutant huntingtin protein with the pathologically expanded polyglutamine region also causes the normal protein to aggregate leading to neurotoxicity

This is a gain of negative function

45
Q

what are 2 explanations for dominant/ recessive inheritances for other syndromes

A

haploinsufficiency – means the reduction to 50% of the normal protein is insufficient for the normal function to occur

Somatic second hit – often in cancer predisposition syndromes , patients inherit one mutant allele and a second mutation occurs somatically leading to cancer

46
Q

how do you know if a diseases is x-linked recessive from a pedigree?

A

Trait is rare in pedigree

Trait skips a generation

47
Q

which sex does x-linked recessive inheritence occur most in?

A

males

48
Q

do parents of x-linked recessive disease have the disease?

A

Parents of affected individuals DO NOT have the disease

49
Q

which parent cannot transfer x-linked recessive disease to their sons

A

Fathers can not transmit it to their sons

50
Q

example of x-linked recessive disease

A

haemophilia A

51
Q

what is haemophilia A disease

A

haemophilia A is a blot clotting disorder

52
Q

what is the cause of hameophilia A

A

mutation in the factor VIII (8) gene on X chromosome

53
Q

is haemophilia A dominant or recessive inheritance?

A

recessive

54
Q

what does it mean when most human characteristics are polygenic

A

are controlled by genes at more than one locus e.g. height

55
Q

what does it mean if a disease is multifactorial?

A

both polygenic and influenced by the environment

56
Q

what are the 3 polygenic diseases

A

obesity
diabetes
cardiovascualr disease

57
Q

what is a Monozygotic MZ twin

A

genetically identical

58
Q

what is a Dizygotic DZ twin

A

not genetically identical

59
Q

if a disease is principally controlled by the environment, which twin would you see it more in: MZ or DZ

A

BOTH

60
Q

How much of the Y chromosome confers maleness?

A

Two chromosomal abnormalities suggest that a small region at the end of the short arm of the Y is all that is needed to confer maleness

61
Q

What is the function of PAR on a Y chromosome

A

PAR = pseudo autosomal regions

its at both end of chromosomes and have equivalent DNA sequence to X chromosome which allows X to pair to Y during meiosis

62
Q

what is function of MSY in Y chromosome

A

MSY = Male specific region

this section does not form pair with X chromosome

63
Q

what are 3 diseases caused by sex chromosome abnormalities

A

klinfelters syndrome

turners syndrome

XYY syndrome

64
Q

what is klinfelters syndrome

A

47 XXY

^ remember the K looks like an X, therefore has 2 X’s = XXy

  • can appear normal
  • causes small testes + limited development of secondary sexual characteristics = infertility
65
Q

what is turners syndrome

A

45 X
- diagnosis during adult life
- no adolescent growth spurt, no periods = infertility

66
Q

what is XYY syndrome

A

47 XYY

ie known as super male syndrome because of the extra Y so have more male characteristics

  • asymptomatic = no symptoms
  • increased growth - above average height
67
Q

Explain Mendelian inheritance.

A
  • The simplest genetic characters are those that depend on the genotype at a single locus.
  • Diseases caused by these factors are referred to as monogenic disorders.
  • They display Mendelian inheritance patterns.
68
Q

What is Mendel’s law?

A
  • Every individual possesses a pair of alleles for a given trait, one of which is passed on to its offspring.
  • Genes for different traits assort independently of each other (unless they are linked).
69
Q

Define locus and allele.

A
  • Locus: chromosomal location (position of gene)
  • Allele: variant of a gene
70
Q

what can proteins be labelled with

A

35 S

71
Q

what can DNA be labelled with

A

32 P

72
Q

theres no sulphur in what?

A

DNA

73
Q

theres no phosphorus in what?

A

Protein

74
Q

what is the composition of the human genome

A
75
Q

Describe (metacentric,submetacentric and acrocentric)

A

FMS (33 decks)

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