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MBG 2040 > Chapter 5 - Extensions/Modifications of Basic Principles > Flashcards

Chapter 5 - Extensions/Modifications of Basic Principles Flashcards

1
Q

What are complete dominance/recessiveness?

A
  • Extremes of a range

- BB=Bb is different from bb

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2
Q

What is incomplete dominance?

A
  • BB, Bb and bb all differ phenotypically

- Bb is intermediate between homozygous phenotypes (e.g. red, white, pink)

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3
Q

What is codominance?

A
  • BB, Bb and bb all differ phenotypically

- Bb exhibits phenotypes of both homozygotes (ex. Blood type)

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4
Q

How many alleles can coexist in each cell?

A

2 (diploid)

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5
Q

Are some alleles associated with certain breeds/varieties of plants/animals?

A

Yes

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6
Q

What is a dominance series/allelic series?

A
  • Relationship between alleles
  • Ex. C > cb = cs > c > ca
  • ’>’ indicates the dominance and ‘=’ indicates incomplete dominance or codominance
  • Describes the dominance hierarchy of multiple alleles
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7
Q

What does the superscript ‘+’ represent?

A
  • Dominant/wildtype allele
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8
Q

What enzyme is coded for by the gene for blood phenotype?

A
  • Transferase
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9
Q

What does I^A encode for?

A
  • Transferase which adds acetylgalactosamine
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10
Q

What does I^B encode for?

A
  • Transferase which adds galactose
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11
Q

What does i encode for?

A
  • Non-functional transferase
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12
Q

What is type AB blood?

A
  • Has acetylgalactosamine and galactose

- Alleles are codominant (both are fully expressed)

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13
Q

What is the wildtype allele?

A

A functional enzyme or other protein is produced

  • Sometimes used to refer to most common phenotype/genotype in a natural population
  • Often dominant over loss of function
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14
Q

What is a loss of function allele?

A

An enzyme or other protein is no longer being produced, is produced at lower levels, or is nonfunctional

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15
Q

What is haplosufficiency?

A
  • Half as much protein is synthesized in heterozygote yet this is often sufficient to achieve wildtype phenotype
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16
Q

What is haploinsufficiency?

A
  • Dominant alleles can be loss of function alleles

- In heterozygote, half as much protein is synthesized and this is not sufficient for normal phenotype

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17
Q

What are recessive lethal alleles?

A
  • Essential genes
  • When mutated lead to lethal phenotype
  • Death only in homozygotes
  • Can still have dominant effect on other phenotypes (i.e. colour)
  • Ex. Tay Sachs disease
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18
Q

What are dominant lethal alleles?

A
  • Expressed in homozygote and heterozygote

- Ex. Huntingdon disease

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19
Q

What is an amorphic allele? What phenotype is produced?

A
  • Recessive
  • Loss of function
  • Does not produce functional polypeptide
  • Severe mutant phenotype
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20
Q

What is a hypomorphic allele? What phenotype is produced?

A
  • Recessive
  • Loss of function
  • Partially functional polypeptide
  • Mild mutant phenotype
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21
Q

What is a dominant-negative allele? What phenotype is produced?

A
  • Produces polypeptide that interferes with wildtype

- Severe mutant phenotype

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22
Q

What is penetrance?

A
  • The proportion of individual organisms having a particular genotype that express the expected phenotype
  • Variation in the population
  • Confounding issues
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23
Q

What is expressivity?

A
  • The degree to which a phenotype is expressed (mild to severe)
  • Variation in the individual
  • Ex. shades of brown hair
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24
Q

What is complete penetrance?

A

Identical known genotype yield 100% expected phenotype

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25
Q

What is incomplete penetrance?

A

Identical known genotypes yield <100% expected phenotype

- Ex. polydactyly

26
Q

What is constant expressivity?

A

Identical known genotypes with no expressivity effect yield 100% expected phenotype

27
Q

What is variable expressivity?

A

Identical known genotypes with an expressivity effect yield a range of phenotypes

28
Q

What is incomplete penetrance with variable expressivity?

A

Identical known genotypes produce a broad range of phenotypes, due to varying degrees of gene activation and expression

29
Q

Assume that long fingers are inherited as a recessive trait with 80% penetrance. Two people heterozygous for long fingers mate. What is the probability that their first child will have long fingers?

A

1/4 x 80% = 20%

30
Q

What are some human disorders that show variable expressivity?

A
  • Split Hand-foot Syndrome
  • Piebaldism
  • Huntingdon Disease
31
Q

What causes incomplete penetrance and expressivity?

A
  • Effects of other genes

- Environmental factors that can alter/suppress effect of a particular gene

32
Q

What are some environmental factors that can affect phenotypic expression?

A
  • Age
  • Sex
  • Temperature (Ex. siamese allele)
  • Chemicals
33
Q

What is the norm of reaction?

A

Range of phenotypes expressed by a single phenotype under different environmental conditions

34
Q

What is a phenocopy?

A

A change in phenotype arising from environmental factors that mimic the effects of a mutation in a gene (e.g. thalidomide can produce phenocopy of phocomelia)

35
Q

Can controlling environment influence appearance of mutant phenotype/disease?

A
  • Yes

- Ex. heart disease (regulate diet/exercise)

36
Q

What is Mendel’s Law of Independent Assortment? How did he discover this?

A
  • The inheritance pattern of one trait will not affect the inheritance pattern of another trait
  • Examined dihybrid crosses
37
Q

What is genetic interaction?

A

Different combinations of alleles from 2 or more genes can result in different phenotypes, because of interactions b/n products at cellular/biochemical level

38
Q

What happens when multiple genes often contribute to a single characteristic?

A
  • Interactions between genes
  • Still dihybrid cross so we have to consider Mendelian principles
  • Still 9:3:3:1 (if there is complete dominance at 2 distinct traits)
39
Q

What is the molecular explanation for complete dominance of cat colouration?

A
  • Dilute gene affects distribution of melanin
  • D: dense pigmentation
  • d: pigment clumping, areas with no granules (lighten)
  • Dilute effect is autosomal recessive, so cat requires 2 copies of d allele for coat to dilute
40
Q

What is complementation and when does it occur?

A
  • 2 strains of an organism with different homozygous recessive mutations that produce same phenotype produce offspring of wildtype phenotype when crossed
  • Occurs if mutations are in different genes
  • Other genome supplies wildtype to complement mutated allele
41
Q

What is a heterogeneous trait?

A

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

42
Q

What is epistasis?

A
  • The masking of the expression of one gene by another

- No new phenotypes are produced

43
Q

What is the hypostatic gene?

A

The masked gene in epistasis

44
Q

What is recessive epistasis?

A

F2 Ratio = 9:3:4

Homozygous recessives at one gene pair mask expression from other gene

45
Q

What is dominant epistasis?

A

F2 Ratio = 12:3:1

One dominant allele at one gene masks expression from another gene

46
Q

What is pleiotropy?

A

A single gene can be responsible for a number of distinct and seemingly unrelated phenotypic effects (Ex. sickle cell disease, cystic fibrosis)

47
Q

What is inbreeding depression?

A
  • Inbred lines of experimental species are often less vigorous than hybrid lines
  • Inbred lines of self-fertilized plants are homozygous for alleles present in founding line
48
Q

What is heterosis?

A
  • When 2 different inbred lines are crossed, hybrids are heterozygous for many genes
  • Hybrids display heterosis, or hybrid vigor
  • Hybrids are much larger than parents
49
Q

What is the Hardy Weinberg principle?

A
  • Predicts genotypes through allele frequencies in a population
    p^2 + 2pq +q^2 = 1
    p = dominant
    q = recessive
50
Q

What are 4 evolutionary influences that make the Hardy Weinberg principle inaccurate?

A
  • Nonrandom mating
  • Unequal survival
  • Population subdivision
  • Migration
51
Q

What are allele frequencies useful in?

A
  • Genetic counselling

- Find risk of child being affected

52
Q

Tay Sachs is an autosomal recessive mutation with a frequency of 0.017 in this population. Therefore, ts = 0.017 and TS = 0.983. What are the chances somebody is a carrier (TS ts) in this population?

A

2pq
= 2(0.017)(0.983)
= 0.033 or 1/30

53
Q

What is the expected frequency of heterozygotes in a population with allelic frequency x and y that is in Hardy-Weinberg equilibrium?

A

2xy

54
Q

What is dosage compensation?

A

A way of equalizing gene expression in the face of different gene dosage
- Extra copy of gene/chromosome can affect development (ex. Females have 2 copies of X)

55
Q

What are pseudoautosomal regions?

A
  • Homologous

- Ex. in sex chromosomes, essential for X-Y chromosome pairing in meiosis in the male

56
Q

What is the XX-XO system for sex chromosomes?

A

XX - Female
XO - Male
Ex. Grasshoppers

57
Q

What is the XX-XY system for sex chromosomes?

A 
XX - Female
XY - Male
XO - Female
XXY - Male
Ex. Mammals
**Males need Y chromosome
58
Q

What is a Barr body?

A
  • Condensed mass in nucleus of female cells in cats, not males
  • It was proposed that this was the X-chromosome (inactive)
59
Q

What is the Lyon Hypothesis/X-inactivation?

A
  • Mary Lyon proposed random inactivation of one female X chromosome
  • If a cell contains more than 2 X chromosomes, all but one are inactive
  • Females are functionally hemizygous (expressing from only 1 gene) for X-linked genes at cellular level
  • 50% will express one allele and other 50% will express the other
60
Q

What happens if there are genes on the X-chromosome?

A
  • Some cells are orange and others are black
  • Allele is present, but not contributing to phenotype
  • Ex. Calico cats
61
Q

When does X-inactivation occur?

A
  • Early in development

- One X chromosome is inactivated in each cell at random

62
Q

What is an example of a genetic mosaic?

A
  • Females that are heterozygous for X-linked traits

- Ex. one eye may be colourblind while other isn’t

MBG 2040 (7 decks)

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