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70 genetics > L5 - departure from mendelian ratios > Flashcards

L5 - departure from mendelian ratios Flashcards

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1
Q

why may we get a deviation from mendelian ratios

A
  1. there are different variations of gene dominance
  2. sons X chromosomes can only be inherited from mother
  3. sex linkage genes
  4. sex influenced genes
  5. mitochondrial and chloroplast DNA only inherited from maternal side
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2
Q

what are the types of loss of function mutation

A

amorphic (null)

hypomorphic (leaky)

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3
Q

describe amorphic (null) mutation

A

recessive

mutation where no protein produced at all / protein has no function

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4
Q

describe hypomorphic(leaky) mutation

A

recessive

protein function reduced due to less protein made/ protein less active

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5
Q

what are the types of gain of function mutation

A

hypermorphic
neomorphic
antimorphic (dominant -ve)
dominant lethal

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6
Q

describe hypermorphic mutation

A

dominant

increase in protein activity due to more protein made/more active

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7
Q

describe antimorphic (dominant -ve) mutation

A

disturbance in function that interferes with protein encoded by norm allele

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8
Q

describe neomorphic mutation

A

dominant

alters function of protein completely (new function)

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9
Q

describe incomplete/partial dominance

departure from mendelian ratios

A

results in blend of characteristics

eg a flower may be CC red and cc white but all Cc offspring are pink rather than red

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10
Q

describe co dominance

departure from mendelian ratios

A

where presence of both dominant alleles are detected equally

eg blood group AB

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11
Q

describe lethal alleles

departure from mendelian ratios

A

a combination of alleles that can be lethal in utero and so are never seen in a population

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12
Q

give an example of lethal alleles

departure from mendelian ratios

A

in mice, homozygous alleles for the yellow coat colour is lethal .
yellow allele is dominant to wild type but recessive lethal

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13
Q

how do lethal alleles affect humans?

A

7.5% of all conceptions are miscarried due to being homozygous for lethal genes

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14
Q

define genetic load

A

collection of all lethal alleles in the pop. gene pool

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15
Q

list the deviations from mendelian ratios due to reasons other that partial/incomplete dominance

A
  1. X linkage
  2. sex influenced
  3. maternal inheritance
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16
Q

describe X linkage

A

unique inheritance patterns because males inherit their X from mother

17
Q

who do X linked disorders affect most and why?

A
  1. males, because they only have one X if the disease is recessive they will still be affected
18
Q

describe characteristics of inheritance of x linked disorders

A
  1. all sons of affected/carrier mother will be affected
  2. cant pass father to son
  3. all daughters of affected father are carriers
  4. males cant be carriers
19
Q

describe influence of sex on departure from mendelian ratios

A

genes found on autosomes but are influenced by sex

can be
sex limited
sex influenced

20
Q

what is sex limited?

give example of sex limited trait

A

(genes on autosomes) phenotype limited to one sex only

eg milk yield in cattle

21
Q

what is sex influenced?

give example of sex influenced trait

A

genes on autosomes
trait usually dependant on hormones

eg male baldness dominant in males recessive in females

22
Q

describe maternal inheritance on departure from mendelian ratios

A

mitochondria and chloroplasts inherited exclusively from maternal side

23
Q

describe characteristics of maternal inheritance (of a disease)

A
  1. all offspring of affected mothers will be affected
  2. offspring of affected father will be unaffected
  3. affects M&F equally

matrilineal

24
Q

define matrilineal

A

feature of maternal inheritance (eg of mtDNA) that doesn’t follow autosomal or sex linked inheritance

25
Q

describe incomplete penetrance

as explanation of departure from mendelian ratios

A

when phenotype associated with genotype fails to appear

eg not all individuals with mutant allele will have mutant disorder (polydactyly)

26
Q

describe variable expressivity

as explanation of departure from mendelian ratios

A

phenotype of mutant genotype varies in severity due to environment / interaction from other genes

eg 4 people with same mutant genotype (wardenburg syndrome) may have different severity of a disorder

  • hearing loss
  • grey hair
  • differently coloured eyes
27
Q

define pleiotropic

A

when an allele affects more than one characteristic

eg hearing loss, greying of hair

28
Q

what does a pleiotropic gene indicate?

A

the gene is required by several tissues/organs

29
Q

what controls penetrance and expressivity?

A

environment

genotype at other loci

30
Q

what causes an allele to be dominant or recessive?

A

the type of mutation

eg gain/loss of function

70 genetics (19 decks)

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