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Genetics > Gene Action > Flashcards

Gene Action Flashcards

1
Q

what is gene action?

A

how the genotype of a particular trait affects the expression in the phenotype

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2
Q

list the 5 types of gene action

A
  1. non-additive
  2. sex-linked
  3. sex-limited
  4. sex-influenced
  5. additive
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3
Q

define non-additive gene action

A

effect of one gene won’t add to the effect of another

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4
Q

define sex-linked gene action

A

inheritance controlled by genes on sex chromosomes

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5
Q

define sex-limited gene action

A

expression of traits limited to one gender

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6
Q

define additive gene action

A

effect of one gene adds to the effect of another to determine the phenotype

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7
Q

what are the 3 kinds of non-additive gene action traits?

A
  1. complete dominance
  2. incomplete dominance
  3. epistasis
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8
Q

what is complete dominance?

A

one allele of a pair can mask the expression of the other (recessive), recessive expression only occurs in the homozygous condition

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9
Q

when is a gene dominant?

A

if only one allele is needed to control the phenotype

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10
Q

give an example of complete dominance non-additive gene action

A

coat color in Hereford and Angus cattle

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11
Q

what happens to the heterozygote in incomplete dominance?

A

it is a different phenotype from the dominant one

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12
Q

what are the genotypic and phenotypic ratios in incomplete dominance?

A

1:2:1

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13
Q

how does epistasis work in non-additive gene action?

A

interactions between non-allelic genes; the phenotypic effect of genes at one locus is dependent upon what alleles are present at another locus DISTINCT from the first locus

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14
Q

what are the 3 types of epistasis?

A
  1. complete dominance epistasis
  2. recessive epistasis
  3. no/incomplete dominance
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15
Q

give an example of complete dominance epistasis

A

wool pigmentation in sheep; alleles at one locus control pigmentation of wool fibers, but white is dominant, so if one W is present, the sheep will be white; if homozygous recessive (ww), color is then dependent on a different allele, see slide if need more info

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16
Q

give an example of recessive epistasis

A

coat color in rabbits, see slides for more info

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17
Q

what is the phenotypic ratio of recessive epistasis?

A

9:3:4

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18
Q

give an example of no/incomplete dominance epistasis

A

coat color in horses

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19
Q

what is the phenotype of CCB_ in horses?

A

bay

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20
Q

what is the phenotype of CcB_ in horses?

A

buckskin

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21
Q

what is the phenotype of cc_ _ in horses?

A

cremello

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22
Q

what is the phenotype of Ccbb in horses?

A

palomino

23
Q

what is the phenotype of CCbb in horses?

A

chestnut

24
Q

what is found on the Y chromosome?

A

very few loci identified as controlling traits unrelated to the sex of the individual

25
Q

what kind of gene action is concerned with the inheritance of traits controlled by alleles on the X chromosome

A

sex-linked

26
Q

give an example of a sex linked trait

A

coat color in cats

27
Q

how does a tortoise shell cat happen?

A

codominance of black and orange alleles (both purebreeding) found on the X chromosome

28
Q

why can’t male cats be tortoise shell?

A

they only get one allele for color because they only get one X chromosome

29
Q

what is recessive sex-linked inheritance

A

unaffected parents produce normal daughters, but half the sons of heterozygous females will show recessive phenotype, females must be homozygous to show trait, so sire must have had it too

30
Q

what does Klinefelter syndrome (XXY) do to male cats?

A

gives them calico coloration, because they inherit both X’s for heterozygous coloration, and the X chromosome deactivation leads to the patchy coat, with the white fur coming from the piebald allele

31
Q

what are sex-influenced traits?

A

the inheritance of a trait appears to be different in the 2 sexes even when they had the same genotype, so expression differs for male and female in the heterozygote, like horned vs polled sheep

32
Q

give an example of sex limited traits

A

milk yield, egg production, cryptorchidism

33
Q

what is pleiotropy?

A

one gene affects more than one trait

34
Q

what is variable expressivity?

A

the existence of more than one grade of a trait

35
Q

what is overdominance?

A

interactions between gene alleles resulting in a heterozygote superior to either homozygote for a particular trait, also called extreme heterozygote

36
Q

what is genetic correlation?

A

selecting for one trait can affect other traits as well, also called correlated response

37
Q

what are the 2 reasons why we have genetic correlation?

A

pleiotropy and gene linkage

38
Q

what is incomplete penetrance? give an example

A

not all animals with a particular genotype exhibit the phenotype; polydactyly in fowl, humans, dogs, cats

39
Q

what are lethal genes?

A

cause embryonic death, or death shortly after birth

40
Q

what are semi-lethal genes?

A

cause death before puberty, predictable

41
Q

what are detrimental genes?

A

reduction in some measure of fitness or productivity

42
Q

what phenotypic ration do lethal genes cause?

A

2:1, because one of the homozygous conditions will always cause death, so an absence of phenotype

43
Q

what is gene linkage?

A

condition where non-allelic genes consistently travel together through meiosis and syngamy

44
Q

how are two loci linked?

A

if they occur on the same chromosome

45
Q

what is the exception to gene linkage?

A

crossing over

46
Q

what does the probability of recombination due to crossing over depend on?

A

the distance between the loci, farther from center = more likely

47
Q

what kind of traits are controlled by additive gene action?

A

quantitative traits, expressed over a range of values

48
Q

what are major genes in additive gene action?

A

those that contribute more than others

49
Q

what is heritability in a broad sense?

A

the ratio of genetic variance to phenotypic variance, can be misleading

50
Q

what is heritability in the narrow sense?

A

a measure of the strength of the relationship between performance and breeding values for a trait in a population

51
Q

what does heritability measure?

A

additive gene action

52
Q

if a trait is highly heritable (>0.4), what does that mean?

A

the performance of offspring will match parents

53
Q

if heritability is low or medium (0.21-0.4) or (0.1-0.2), what does that mean?

A

offspring performance will not match sire

Genetics (8 decks)

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