inheritance and disorders Flashcards

1
Q

what is sex linked inheritance

A
  • male: XY
  • female: XX
  • sex-linked genes in humans are usually carried on the X chromosome
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2
Q

what is y linkage / x inactivation

A
  • Y: very rare, father to son (never to females)
  • X: inactivation of one X during embryonic development, do not produce twice as many X linked proteins, phenotype of both alleles can be expressed (mosaic of cells with varying X chromosomes inactivated)
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3
Q

what are mutations

A
  • change in gene or chromosome
  • new characteristic displayed
  • harmful, beneficial or no effect
  • dysfunctional / no protein
  • gene or chromosome mutation
  • occurs during replication before cell division
  • mutagen: environmental factor that increases rate at which mutations occur
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4
Q

what is a genetic disorder

A
  • harmful effect of detrimental allele
  • mild: albinism (loss of pigmentation)
  • severe: cystic fibrosis
  • rarity: affected individuals usually die at younger age and cannot reproduce)
  • uneven distribution, different genetic histories, geographic isolation
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5
Q

what is tay Sachs

A
  • homozygous = show disease
  • incurable, disorder of lipid metabolism, accumulation of fat in the nervous system leads to deterioration, very rare
  • lethal if not masked, if born, child develops normally for few months before developing mental and physical disability
  • ashkenazi: jewish population, occurs 1:3,500 in comparison to 1:300,000 worldwide
  • phenotypic categorisation: incomplete dominance at organism level and co-dominance at molecular level
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6
Q

what is sickle cell anaemia

A
  • substitution of valine for glutamic acid
  • haemoglobin gene, changes shape of RBC / haemoglobin, not efficient in carrying oxygen in blood
  • leads to clumping / clogging
  • 1:400 people of african descent are affected
  • areas of malaria: 2 SCA alleles = fatal, 2 normal alleles = susceptible to malaria, 1 of each = resistant to malaria and no signs of SCA (selective / survival advantage, co-dominance at molecular level)
  • pleiotropy: multiple effects of one gene
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7
Q

what is cystic fibrosis

A
  • chromosome 7, recessive
  • abnormal ion channels, thick mucous, salty skin, persistent coughing
  • 4% of european descent are carriers, 1:3,500 are affected
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8
Q

what is duchenne muscular dystrophy

A
  • fault in gene for dystrophin (recessive) on X chromosome
  • mother passes to son
  • wasting of limb muscles, die of respiratory failure
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9
Q

what is ichthyosis

A
  • mutation of sulfatase gene
  • lack functional allele (I), have recessive (i)
  • large patches of dry, scaly skin
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10
Q

what is a lethal recessive and an example

A
  • less common
  • dominant = kills offspring before maturity (not passed on, unlike recessive alleles)
  • huntington’s: escapes elimination, death occurs later, reach life expectancy to have children
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11
Q

what are pedigrees

A
  • used to study human disorders, family tree focusing on traits
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12
Q

what is non-disjunction

A
  • aneuploidy
  • homologous chromosomes / sister chromatids fail to separate correctly (meiosis 1 or 2)
  • checkpoints don’t work effectively
  • monosomy: -1 chromosome, loss of autosome = gamete dies, gamete that gains chromosome may survive
  • trisomy: +1 chromosome
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13
Q

what is an example of non-disjunction in autosomes

A
  • down syndrome: additional chromosome 21, can be whole / part of chromosome (varying degree of symptoms)
  • symptoms: distinct facial appearance, stunted growth, degree of mental disability
  • partial trisomy: part of chromosome is present, symptoms may occur but not to full extent
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14
Q

what are examples of non-disjunction in sex chromosomes

A
  • klinefelter (XXY): deficiency of male hormones, sterile, female traits (enlarged breasts, sparse body hair), reduced mental capacity, small testes,
  • turners (XO): 1 in 2000 births, short stature, infertile, lack secondary characteristics, infertile (do not menstruate)
  • jacobs (XYY): 1 in 1000 births, ‘super male’, fertile males of normal appearance, high frequency in sexual homicide perpetrators
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