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Spring Semester > Genetics Exam 3 > Flashcards

Genetics Exam 3 Flashcards

1
Q

heterogeneous trait

A

a trait that can arise from a mutation in any number of DIFFERENT genes (also known as genetic heterogeneity)

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2
Q

complementation test

A

determine if mutations that cause the same phenotype are in the same or different genes

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3
Q

how do you test if a phenotype is due to mutations in two different genes or different mutations in the same gene?

A

cross affected individuals & observe phenotype with a complementation test

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4
Q

complementation (+)

A

mutations are in two different genes
ex: two parents with a “mutant” phenotype produce normal progeny-happens because the two parents have defects in DIFFERENT genes

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5
Q

what is the difference between heterogeneous traits and incomplete penetrance?

A

heterogenous involves more than one gene (two genes)

incomplete penetrance involves one gene

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6
Q

non complementation (-)

A

mutations are in the same gene
ex: offspring have the same mutant phenotype as parents. Parents have defects in the same gene: the phenotype will be expresed

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7
Q

what can complementation tests reveal?

A

can reveal the minimum number of genes that contribute to a trait (look for pairs)

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8
Q

epistasis

A

two (or more) genes that are both involved sequentially in a pathway in producing a particular pathway

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9
Q

what can happen as a result of epistasis?

A

one genotype can mask the expression of the other genotype, leading to different ratio of progeny than one would expect (9:3:4)

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10
Q

Which gene is epistatic?

A

the gene that masks the other one is the epistatic gene

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11
Q

what do nurse cells do in invertebrates?

A

deposit mRNA and proteins into the cytoplasm of the egg before the egg is released and fertilized

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12
Q

maternal effect genes

A

the phenotype of the progeny is determined by the mother’s genotype –the genotype of the father does not affect this particular phenotype of the offspring

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13
Q

where is most developmental genetics carried out?

A

in non-mammalian systems because can mutagenize animals so they produce offspring with lots of mutant phenotypes

  • can then determine by looking at phenotype what kinds of genes were mutated & what their normal function are
  • study what those genes are responsible for
  • create model systems for studying human developmental disorders
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14
Q

loss of function mutations (lf)

A

m/+ has normal phenotype
half of the normal amount of product is enough for normal function; the animal has to be lacking both copies for a phenotype to be seen
- almost always recessive

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15
Q

gain of function mutations (gf)

A

m/+ has a mutant phenotype
the presence of the altered product (from the mutated copy) is enough to change the phenotype
-almost always dominant
often changes the function of the protein such that it has a new function or an altered function

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16
Q

three fundamental laws of development

A
  1. Timing is everything
  2. Location, location, location
  3. Both the above are true
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17
Q

an embryo is comprised of cells that are genetically all the same, but these cells end up doing different things later. how?

A

cells must acquire positional information to contribute to that body plan of an organism

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18
Q

What are the two molecular mechanisms that define positioning?

A

signaling & cytoplasmic factors

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19
Q

two types of cytoplasmic inheritance

A

mitochondrial inheritance

maternal inheritance

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20
Q

mitochondrial inheritance

A

mitochondria are only passed from affected mothers to all offspring (mitochondria are only passed along from the mother b/c sperm contributes no cytoplasm to egg)
-severity frequently related to the proportion of mutant mitochondria inherited at birth

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21
Q

maternal inheritance

A

maternally contributed mRNAs and proteins are critical for early developmental events of many embryos such factors are deposited into the egg during oogenesis, thus present even before cell division begins

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22
Q

maternal effect genes

A

the genes that produce these mRNAs and proteins critical for early developmental events of many embryos

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23
Q

maternal effect genes in mammals?

A

not existent because they are placental animals so the embryo uses its genes from the start and relies on mom for nutrients

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24
Q

maternal effect genes in non-mammalian animals?

A

externally deposited eggs so the mother puts into the egg proteins and RNA that the egg needs for the first few hours. embryo uses its genes only later

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25
Q

the axes of invertebrates is determined by…

A

maternally contributed mRNAs and proteins

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26
Q

exploratory genetics

A

mutagenize organisms, look for phenotype of interest, determine nature of mutation, map location of gene (first)

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27
Q

manipulative genetics

A

(can only do if you already know the identity of the gene)

knock out gene, over express gene, analyze what controls expression, etc 2nd

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28
Q

homeotic genes

A

confer positional information of the early embryo ultimately result in activation of this set of genes

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29
Q

what do homeotic genes do?

A

determine the identity of different regions all along the body axis & is CONSERVED across all organisms
-encode transcription factors & contain a “homeobox” region

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30
Q

homeobox region

A

encodes the homeodomain

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31
Q

Hox gene expression in ALL organisms

A

the order of the genes expression, from anterior to posterior parallels the order of genes on the chromosome

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32
Q

epigenetics

A

inherited changes in gene function that cannot be explained by differences in the DNA sequence

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33
Q

3 examples of epigenetics

A
  • maintenance of the state of a gene (transcriptionally off or on) through many cell divisions in development through meythlation
  • Imprinting
  • X inactivation
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34
Q

Imprinting

A

inactivation of certain genes in male or female germline

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35
Q

X-inactivation

A

in mammalian dosage compensation

inactivation of an X chromosome through methylation and long non coding RNA

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36
Q

methylation

A

methylation of cytosine bases in DNA of developmentally important genes, primarily in the promoter region
-only cytosines in CG di-nucleotides become methylated

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37
Q

how is methylation maintained?

A

through replication by enzymes that recognize the methylated state of these cytosines

38
Q

is DNA methylation distributed evenly?

A

not distributed evenly, tend to be in promoter regions

methylation prevents transcription

39
Q

CpG islands

A

stretches of CGs that are methylated (60-80%)

40
Q

detecting methylation

A

treatment with sodium bisulfate: unmetylated cytosines are converted into uracil.
compare treated vs. untreated and any methylated C will still be a C after treatment

41
Q

Genomic imprinting

A

a specialized example of methylation

methylation occurs during the production of gametes

42
Q

maternally imprinted gene

A

methylated (inactivated) in the production of oocytes

43
Q

paternally imprinted gene

A

methylated (inactivated) in the production of sperm

44
Q

imprinting maintenance

A

is maintained throughout the somatic cells of the new individual BUT is erased and then re-initiated with gametogenesis so for an imprinted gene, everyone (male & female) has one copy that is methylated and one that is not

45
Q

how many imprinted genes are required for normal function?

A

only one copy of the gene is required for normal function, and the other copy is methylated

46
Q

why might imprinting exist?

A

in general, genes that enhance embryonic growth (lgf2) are imprinted in females; genes that repress embryonic growth (H19) are imprinted in males

47
Q

chromosome count

A

Losing or gaining an autosome is a bad thing for humans
-trisomy of all autosomes except 21 is fatal
-monosomy of all autosomes is fatal
But monosomy and trisomy of X are ok

48
Q

In mammals, X inactivation is another form of epigenetics, why?

A

modification of the genome outside the actual DNA sequence

49
Q

Barr body

A

represents the inactive X chromosome

50
Q

X inactivation is …?

A

random & takes place early in development, between 4-cell and 32-cell stage
the inactivation will be maintained in all the daughter cells of each cell

51
Q

is the whole X chromosome inactivated?

A

the entire X chromosome is not inactivated-there is a small section where transcription still takes place
-this has consequences for individuals with abnormal sex chromosome combinations

52
Q

why don’t sex and gender always match?

A
  1. Mutations
  2. Hormones
  3. Chromosomal number abnormality
53
Q

mutations

A

a person could have a translocation of the SRY gene onto an X chromosome: XX but appear male

54
Q

hormones

A

a person could be chromosomally male or female, but have a deficit or excess of hormone production or reception
-Most common example Androgen Insensitivity Syndrome (AIS) =chromosomally XY but phenotypically female

55
Q

chromosomal number abnormality

A

sometimes people have too many or too few sex chromosomes; this results primarily in the infertility, but can also result in ambiguous external sex characteristics depending on hormone production

56
Q

what is the actual mechanism of X inactivation in mammals?

A

a complex on the X chromosome the XIC (X inactivation center) is responsible for X inactivation

57
Q

Xist

A

the main gene of interest in X inactivation

the state of Xist is opposite to the rest of the X chromosome

58
Q

Tsix

A

another gene involved (Xist backwards) it is active when Xist is inactive

59
Q

When Xist promoter is ACTIVE (unmethylated)

A

Xist is made & that X chromosome is inactivated

60
Q

When Xist promoter is INACTIVE (methylated)

A

Xist is not made & that X chromosome is active

61
Q

The Xist gene

A
  • does not get translated into a protein
  • instead makes a long RNA that coats the X chromosome
  • initiates further meythlation
62
Q

Xist action

A

-the Xist mRNA coats the chromosome that it is transcribed from: it only acts in “cis”
Once Xist mRNA is transcribed:
-the promoters of additional genes along that X chromosome are methylated
-these methylations are preserved so that the same chromosome remains inactivated even after many rounds of cell division

63
Q

poylgenic trait

A

traits determined by the combined effect of 2 or more pairs of alleles

64
Q

single gene, complete dominance

A

discrete phenotypes

discrete distributions

65
Q

single gene, incomplete dominance

A

discrete phenotypes

discrete distributions

66
Q

multiple genes, incomplete dominance

A

continous phenotypic traits

continous (normal) distributions

67
Q

additive alleles

A

each allele contributes EQUALLY to the trait

you can see the effect of BOTH alleles

68
Q

if you know the number of phenotypic classes

A

use 2n+1 =# of phenotypic classes

69
Q

if you know the frequency of individuals in an extreme class

A

(1/4)^n=frequency of extreme

70
Q

heritability

A

proportion of total phenotypic variance due to genetic differences among individuals

71
Q

phenotypic variation

A

variation of a trait can be separated into genetic and environmental components
Var(P) = Var(G) + Var(E) +2Cov(G,E)

72
Q

genotypic variance Var(G)

A

variation in phenotype from differences in genotype

73
Q

environmental variance Var(E)

A

variation in phenotype from environment

74
Q

genotype-environment 2 Cov(G,E) interaction

A

environmental effects on phenotype differ according to genotype

75
Q

heritability numbers

A

estimates apply only to a particular group in an particular environment–does not apply to individuals, only to variations in a group
even the most highly heritable traits can be modified by the environment

76
Q

single gene trait

A

one gene with two or more alleles results in two distinct phenotypes

77
Q

discontinous characteristcs

A

exhibits only a few, easily distinguished phenotypes

yes/no

78
Q

polygenic trait

A

varying phenotypes result from input of multiple genes that contribute additively (collectively) to the phenotypes

79
Q

complex trait (quantitative)

A

multiple genes (usually) and environment yield a continuous distribution of phenotypes

80
Q

polygenic trait graphs

A

the greater the variance, the more spread out the distribution is about the mean

81
Q

variance (sd^2)

A

the average squared distance of all measurement from the mean
-measure of variation within a population

82
Q

why is variance important?

A

because many polygenic traits are also influence by the environment

83
Q

heritability

A

the proportion of the total phenotypic variance in a population due to genetic differences among individuals

84
Q

heritability estimate

A

expresses the likelihood of a trait being passed on from parent to sibling
-if a trait has high heritability, the offspring are more likely to express that same trait

85
Q

how do you measure Var(G)?

A

take genetically identical seed and genetically diverse seeds and grow both in the same environment

86
Q

small Var(E) –>

A

contribution from genetics appears larger (larger h)

87
Q

large Var(E) –>

A

contribution from genetics appears smaller (smaller h)

88
Q

Quantitative Trait Locus

A

a segment of DNA that affects a quantitative (continuously varying) trait

89
Q

basic principles of QTL mapping

A
  1. need markers closely linked to QTLs of interest
  2. Need a mapping population in which each true breeding line has defined marker alleles
  3. Cross two inbred (pure breeding) strains to produce F1, then backcross the F1 to parental strain
90
Q

what can markers be?

A

RFLPs, SNPs, micro satellite, etc.

Anything that can be measure on a gel

91
Q

purpose of back cross?

A

generate offspring that have chromosomes mostly from one parent strain and only a few from the other parent stain

Spring Semester (13 decks)

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