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MBG 2040 > inheritance > Flashcards

inheritance Flashcards

1
Q

Autosomal dominant traits

A

single copy of an allele will dominate
- capital letter signifies dominance

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2
Q

dominant hypermorphic alleles

A

negative phenotypic consequences due to
a) the over-production of a normal protein OR
b) the production of a protein with increased activity levels

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3
Q

Neomorphic alleles

A
  • negative phenotypic concequence due to
    a) the presence of an altered protein that has a new function (enzyme binds to wrong substrate)
    b) the altered protein interferes with the wildtype protein (dominant-negative allele)
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4
Q

Rare autosomal dominant traits

A

Most affected individuals are heterozygote (Bb) because if trait is rare in the population then matings between Bb and bb individuals would occur most often

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5
Q

incomplete dominance

A

BB, Bb, and bb all differ phenotypically with Bb being the intermediate between homozygous phenotypes

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6
Q

Complete dominance and recesiveness

A

the extremes of a range
Phenotype BB and Bb are the same while bb is different

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7
Q

Codominance

A

BB, Bb and bb all differ phenotypically but Bb exhibits phenotypes of both homozygotes

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8
Q

wildtype allele

A

the most common normal allele in the wild for that species - functional enzyme or other protein is produced

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9
Q

alleles in a population vs in an individual

A

Population: multiple alleles may exist
Individual (diploid): only 2 alleles coexist in each cell

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10
Q

dominance series / allelic series

A

describes the dominance hierarchy of multiple alleles

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11
Q

ABO blood type phenotype

A
  • three alleles: I^a, I^b, i
  • 4 blood types, A, B, AB, O
  • I^a and I^b both dominate i, however the i allele is the most abundant in the human population (allele frequency)
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12
Q

what does the I^a blood type allele encode

A
  • A transferase which adds Acetylgalactosamine to the surface of red blood cells
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13
Q

what does the I^b blood type allele encode

A
  • A transferase which adds galactose to the surface of the red blood cell
  • galactose acts as antigens
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14
Q

what does the i blood type allele encode

A
  • a non-functional transferase
  • has neither component on the cell surface
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15
Q

why are people with type O blood type universal donors

A

because the blood won’t get rejected by the body since they do not have antigens on the surface.
- individuals with type A and B could possibly carry the i allele

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16
Q

Type AB blood

A
  • Rare
  • universal receivers of blood since both antigens are present on the surface of red blood cells
  • alleles are codominant - both are fully expressed in heterozygote
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17
Q

loss of function allele

A

an enzyme or other protein is no longer being produced, is produced at lower levels or is non functional

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18
Q

dominant vs recessive loss of function allele

A

dominant: loss of function produces a phenotype, needs both copies
recessive: loss of function can still work with only one copy

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19
Q

haplosufficiency

A
  • one copy is enough to function
  • half as much protein is synthesized yet is still sufficient to achieve the wildtype phenotype
  • often wildtype allele is dominant over loss of function allele
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20
Q

true or false: the dominant allele is always normal and the recessive allele is a mutation

A

false - not always the case

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21
Q

recessive lethal alleles

A
  • 2 copies of the dominant allele results in the death of an empbryo
  • Yy x Yy gives phenotypic ratio 2:1
  • Y allele is dominant for trait but recessive for lethality
22
Q

recessive lethal allele example: Manx cat

A

mm = normal tail
Mm = no tail
MM = lethal (death)
- every cat that expresses this gene is heterozygote

23
Q

Dominant vs recessive lethal genes

A

Dominant: can be expressed in both the heterozygote and homozygote (YY = lethal)
Recessive: only expressed in the homozygote (tsts = lethal)

24
Q

true or false: your genotype for one gene can influence how the genotype contributes to another gene-phenotype

A

true - through penetrance and expressivity

25
Q

Penetrance

A

the proportion of individual organisms having a particular genotype that express the expected phenotype - variation in population
- a yes or no

26
Q

Expressivity

A

the degree to which a phenotype is expressed - variation in the individual
- a scale mild to severe (a yes to a degree)

27
Q

complete vs incomplete penetrance

A

complete: identical known genotypes yield 100% expected phenotype
incomplete: identical known genotypes yield <100% expected phenotype

28
Q

constant vs variable expressivity

A

constant: identical known genotypes with no expressivity effect yield 100% expected phenotype
variable: identical known genotypes with an expressivity effect yield a range of phenotypes

29
Q

Example of incomplete penetrance: polydactyly

A

having extra fingers and toes
not fully penetrant
- if only half the genotype for polydactyly have extra digits, you would say it shows 50% penetrance
(there us another gene protecting other individuals from expressing this gene)

30
Q

Piebaldism - variable expressivity

A

rare autosomal dominant disorder
- single gene where if you have the mutation you have an absence of melanocytes of different sizes and in different areas of the skin and hair

31
Q

Huntington disease - variable expressivity

A

rare autosomal dominant disorder
- variable in the time onset of disease
- can cause loss of muscle coordination, cognitive decline and dementia - affected individuals may not exhibit all symptoms and to different severities

32
Q

what causes incomplete penetrance and expressivity?

A

effects of other genes and environmental factors that suppress the effect of a particular gene

33
Q

Environmental factors that can affect phenotype expression

A
  1. age
  2. sex
  3. temperatures
  4. chemicals
    norm of reaction: range of phenotypes expressed by a single phenotype under different environmental conditions
34
Q

Environmental effects on phenotype ex: the Himalayan rabbit

A
  • Himilayan allele produces dark fur at tips of the body
  • body of rabbit is white due to body heat being high enough and slightly denatures the enzyme
  • dark pigment only develops at low temperatures
  • if breeded at higher temperatures would be completely white
35
Q

phenocopy

A

a change in phenotype arising from the environmental factors that mimic the effects of a mutation in a gene

36
Q

genetic interaction

A
  • many genes contribute to a single phenotype
  • different combinations of alleles from two or more genes can result in different phenotypes, because of interactions between their products at the cellular or biochemical level
37
Q

eye colour genotypes (theory)

A

A-B- = brown
A-bb = green
aaB- = grey
aabb = blue
- 2 genes confer a single phenotype (eye colour) but confer what colour

38
Q

Biochemical level of gene interaction hypothetical example : eye colour

A
  • humans start off with a baseline blue pigment
  • if you have at least A-B-, convert from blue to green to brown
  • alternative path - in the absence of green, the functional B enzyme can use blue to make grey
39
Q

Complete dominance at two genes contributing to a single phenotype example: pigmentation

A

Dominant / dense allele = D, produces dense pigmentation
recessive / dilute allele = d, results in pigment clumping causing coat to dilute or lighten
- dilute effect is autosomal recessive, hence cat requires 2 copies of the d allele for the coat to dilute

40
Q

complementation

A

occurs when two strains of an organism with different homozygous recessive mutations that produce the same phenotype produce offspring of the wildtype phenotype when mated or crossed

41
Q

requirements for complementation

A
  • will only occur if mutations are in different genes
  • the other genome supplies the wild-type genome to “compliment” the mutated allele
  • just need one of each dominant allele to exhibit trait
42
Q

complement example: cats

A

2 white cats (ccAA and CCaa) mate and produce a black cat (CcAc)
- genes from family one complement genes from family 2 to receive the black phenotype
- homozygous recessive mutations in different genes for each family create heterozygote

43
Q

complementation ratios

A

genotype = 9:3:3:1
phenotype = 9:7

44
Q

heterogenous trait

A

a mutation in any one of a number of genes can give rise to the same phenotype
ex: about 50 genes can have recessive mutant alleles that can cause deafness in humans

45
Q

epistasis

A

the masking of the expression of one gene by another, no new phenotypes are produced
- epistatic gene does the masking
- hypostatic gene is masked

46
Q

epistasis ratios

A

dominant epistasis: 12:3:1
- A-B- and A-bb have the same phenotype
recessive epistasis: 9:3:4
- A-bb and aabb have same phenotype

47
Q

dominant vs recessive epistasis

A

dominant: one dominant allele at one gene masks expression from the other gene
recessive: homozygous recessive at one gene pair mask expression from the other gene

48
Q

pleiotropy

A

a single gene can be responsible for a number of distinct and seemingly unrelated phenotypic effects

49
Q

hardy weinberg principle

A

predicting genotypes through allele frequencies in a population
p^2 + 2pq + q^2 = 1
p + q = 1

50
Q

the hardy Weinberg principle is correct as long as there is no…

A
  1. nonrandom mating
  2. unequal survival
  3. population subdivision
  4. Migration

MBG 2040 (23 decks)

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