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Biol251 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

Wild type allele

A

occurs most frequently in a population

often dominant

standard against which mutations are compared

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2
Q

Loss of function mutation

A

mutation causes diminution or loss of wild-type function

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3
Q

Null allele

A

loss of function mutation with complete loss; produces no functional gene product, usually recessive

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4
Q

Gain of function mutation

A

enhances function of wild-type product, usually by increasing its quantity

usually dominant

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5
Q

Drosophila allele system

A

allele written uppercase or lowercase depending on whether mutation is dom or recessive

wild-type alleles (nonmutant) are designated with a superscript +

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6
Q

Incomplete / partial dominance

A

crossing two parents with contrasting traits produces offspring with an intermediate phenotype

for example, red + white flowers = pink flowers

neither allele is dominant

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7
Q

Codominance

A

two alleles of a single gene are responsible for producing distinct gene products

Joint expression of both alleles in a heterozygote

both are expressed; don’t ‘blend’ like in incomplete

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8
Q

Molecular basis of complete dominance

A

the heterozygote creates a nonfunctional protein with the recessive gene, and a functional protein with a dominant gene

dominant gene product determines the trait

recessive homo doesn’t produce any functional proteins

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9
Q

Molecular basis of incomplete dominance

A

caused by “dosage” effect:
- two doses produces the greatest amount of functional protein
- one dose produces less, not fully reaching homo phenotype
- zero doses, no functional protein

i.e, products in a dom homo are sufficient to produce the phenotype, hetero are insufficient to fully reach the phenotype; in a recessive, no products

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10
Q

Cause of lethal alleles

A

represent interruptions to essential genes, such as deletion mutations

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11
Q

recessive lethal allele

A

may produce unique mutant phenotypes when heterozygous

kills when homozygous (not necessarily when homo recessive; dominant genes can be recessive for lethal; just means 2 copies are needed)

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12
Q

dominant lethal allele

A

one copy of the allele is enough to kill

much rarer because harder to pass down

usually develop later in life after offspring have been produced

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13
Q

Pleiotropy

A

single gene can have many different effects

the gene product has multiple functions, thus affecting many phenotypes

  • protein may be used in several different places
  • other processes may depend on protein
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14
Q

gene interaction

A

several genes influence single characteristic

does not imply interaction between products directly, rather: cellular function of gene products contribute to phenotype

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15
Q

Epigenesis

A

each step of development contributes to the final appearance

gene products may exist in a biochemical pathway dependant on the functioning of several genes

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16
Q

Epistasis

A

expression of one gene or gene pair masks or changes the expression of another gene or gene pair, due to the implications of one product on the other

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17
Q

Recessive epistasis

A

recessive genotype masks expression of another dominant gene

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18
Q

Dominant epistasis

A

dominant allele at one locus masks expression of all alleles at a second locus

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19
Q

Complementary gene expression

A

Both genes work together to produce a final product

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20
Q

Complementation

A

Two genotypes may cause the same phenotype

Thus they can produce offspring without the phenotype

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21
Q

Complementation Analysis

A

an experimental approach used to analyze the cause of a phenotype

IF NORMAL = COMPLEMENTATION
IF ABNORMAL = NO COMPLEMENTATION

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22
Q

[complementation] normal development

A

mutations are in separate genes, not alleles of each other

following cross, heterozygous for both genes; normal products of both genes are produced by normal copy of each

complementation occurs

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23
Q

[complementation] abnormal development

A

mutations affect same gene and are alleles, so no normal gene product

complementation does not occur

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24
Q

Complementation groups

A

All mutations belonging to a single gene

will complement mutations in other groups

with large numbers of complement groups studied, it is possible to predict # of genes involved in determining a trait

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25
Q

X-linkage

A

mutations attached to the x chromosome

results in unique patterns of inheritance, dependant on sex

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26
Q

Hemizygous

A

males cannot be homo/heterozygous for x-linked genes

express whatever’s on their single X

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27
Q

Crisscross pattern of inheritance

A

traits controlled by x-linkage are passed from homozygous mothers to all sons

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28
Q

sex-limited inheritance

A

A trait that is expressed in one sex, even though the trait is not X- or Y-linked

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29
Q

sex-influenced inheritance

A

phenotypic expression conditioned by the sex of the individual

Heterozygote may express one phenotype in a male and another in a female

could be dominant in one sex or recessive in the other

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30
Q

Degree of expression

A

some mutant genotypes produce individuals whose phenotypes are essentially normal; extent of mutation’s presence is measured in penetrance and expressivity

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31
Q

penetrance

A

percentage of individuals who show some degree of expression of a mutant genotype; how often the phenotype occurs in population

observed phenotype expression / expected phenotype expression (o/e)

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32
Q

Expressivity

A

range of expression of mutant genotype

i.e, eyeless gene in mutant flies; average expression is reduction of eye size, but expression ranges from complete loss of both eyes to completely normal eyes

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33
Q

conditional mutations

A

phenotypic expression is determined by environmental conditions

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34
Q

temperature-sensitive mutations

A

conditional mutation that produces a mutant phenotype at a given temperature

i.e, enzyme only active in warmer temperatures; enzyme affects phenotype

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35
Q

Permissive condition

A

the condition where the conditional mutation is shown

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36
Q

Restrictive conditions

A

conditions under which the conditional mutation does not show

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37
Q

Genetic anticipation

A

with each generation that inherits some genetic disorder, the symptoms intensify and the age of onset decreases

caused by expansion of trinucleotide repeats in or near a gene

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38
Q

Ratio of recessive epistasis

A

9:4:3

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39
Q

Ratio of dominant epistasis

A

12:3:1

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40
Q

Double recessive epistasis

A

One dominant allele at each of 2 loci is needed for wild phenotype

two genes whose combined dominant function give the dominant phenotype, but whose recessive phenotypes overrides the dominant phenotype in the other, giving a recessive phenotype.

MUTUAL MASKING

form of complementary gene action

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41
Q

Heterogametic sex

A

Unlike gametes; ZW, XY, X0

always determines sex of progeny

Male not always heterogametic

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42
Q

Homogametic sex

A

Like gametes, XX, ZZ

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43
Q

Klinefelter

A

XXY

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44
Q

Turner

A

X

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45
Q

Reciprocal translocation on sex chromosomes

A

Causes XY to develop female and XX male

SRY mutation; SRY jumps from Y to X or vice versa

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46
Q

Physical process of sex differentiation

A
  1. embryo hermaphroditic early in development
  2. bipotential gonadal ridges appear, sexually indeterminate
  3. gonadal ridges differentiate into testes with Y chromosome present
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47
Q

Bipotential gonads

A

Undifferentiated gonadal ridges early in development

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48
Q

PAR

A

Pseudoautosomal region of Y chromosome; shares homology with X, pairs during meiosis

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49
Q

Male-specific region of Y

A

divided equally between euchromatin and heterochromatin; doesn’t pair during meiosis

contains SRY

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50
Q

SRY

A

Sex-determining region of Y

gene region that controls male development

encodes for TDF

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51
Q

TDF

A

testis-determining factor

causes testicular formation; encoded by SRY

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52
Q

Primary sex ratio

A

ratio of sex at conception; equal amounts of female and embryos conceived; more XX die during development

53
Q

Secondary sex ratio

A

Sex at birth; more XY than XX born

54
Q

Dosage compensation

A

The idea that XX should have a higher ‘dosage’ of genes, leading to problems with X-linked genes

In order to balance the dose of genes, a dosage compensation mechanism inactivates all but 1 X in a cell

55
Q

Barr body

A

an inactivated X chromosome

all but 1 X will become a Barr body

not all genes on Barr body are inactivated; Xic

56
Q

Lyon hypothesis

A

postulated that inactivation of X occurs randomly in cells at a point early in embryonic development

not all cells have the same inactivated X

57
Q

Lyonization

A

Random inactivation of an X chromosome

58
Q

Xic

A

X inactivation center

major control unit of X chromosome; expressed only on inactivated X

has a gene XIST which is critical for inactivation

59
Q

Imprinting

A

the same X chromosomes are inactive in subsequent divisions

one or both chromatin components are chemically modified, silencing them Forever

60
Q

Drosophila sex determination system

A

The X:A ratio determines sex

more X than A = female, less X than A = male fly

2X:2A (1) is a female fly, 1X:2A (.5) is a male fly

The presence of an additional X alters the balance and results in female differentiation

61
Q

Location of sex-related genes in drosophila

A

X chromosomes have ‘femaleness genes’

‘maleness genes’ are on autosomes

the Y chromosome in flies affects male fertility; non-Y male flies are infertile

62
Q

Metafemales

A

many X chromosomes, such that X:A ratio exceeds 1:1

weak and sterile

63
Q

Intersex drosophila

A

0.5 < X:A < 1.0

(between standard male and standard female)

64
Q

Metamales

A

X:A ratio is less than 0.5, more autosomes than X

weak and sterile

65
Q

Genetic basis of Drosophila sex differentiation

A

A cascade of regulatory gene expression converts X: A ratio into a molecular signal

3 regulatory genes, which are spliced differently between sexes

Females have regulated splice sites, whereas males do not (making males the ‘default’)

66
Q

SXL

A

sex-lethal

the “master switch”; X-linked
expression of Sxl relies on ratio of X:A of 1

in males, sxl not activated
in females, sxl activated

X chromosomes code for promoters for SXL, whereas autosomes code for repressors; if there are more autosomes than X (as in males), SXL is repressed

67
Q

TRA

A

transformer

if Sxl present, produces female TRA protein

if no Sxl present, no TRA protein made

this protein influences expression of dsx

68
Q

dsx

A

doublesex
regulator of sex-related gene expression

RNA spliced differently in males and females, as told by presence of TRA product; product of splices induces different differentiation

if female TRA protein is present, will create female DSX protein

if no TRA protein is present, will create male DSX proteins (DSXM)

69
Q

dsxm

A

male DSX proteins

represses genes required for female development, activates male specific genes

70
Q

Drosophila dosage compensation

A

no barr bodies, completely different system

X-linked genes in males are transcribed at twice the level of comparable genes in females due to DCC

71
Q

DCC

A

dosage compensation complex; creates gene-activating proteins

will activate male X-linked genes more often, to give an equivalent dosage

72
Q

Temperature dependent sex determination

A

steroids affected by temperature are important in sex determination in these systems

73
Q

Aromatase

A

converts androgens into estrogens

activity correlates with reactions in gonadal development; high in ovaries, low in testes

thermosensitive factors may mediate transcription of aromatase in TSD systems

74
Q

Interplay of genetic and temp differentiation systems

A

animals can have XX/XY chromosomes, but during development can be converted between sexes at different temperatures

75
Q

Chromosome mutations

A

changes in total # of chromosomes

deletion or duplication of segments of chromosomes

rearrangement of chromosomes

76
Q

Aneuploidy

A

Organism gains or loses one or more chromosomes, but not a complete set

Better tolerated in plant kingdom

Can alter phenotype drastically; sex-chromosome aneuploidy has a less drastic effect than autosomal aneuploidy

Monosomy & Trisomy

77
Q

Monosomy

A

Type of aneuploidy

loss of a single chromosome from an otherwise diploid genome; 2n-1

usually not tolerated for autosomes

78
Q

Haploinsufficiency

A

a single copy of a recessive gene due to monosomy may be insufficient to provide life-sustaining function

79
Q

Trisomy

A

gain of a single chromosome to an otherwise diploid genome 2n+1

somewhat more viable in autosomes for small chromosomes

Usually viable in plants, but with altered phenotypes

80
Q

2 complications of monosomy

A

if just one gene on an inherited chromosome is a lethal allele, monosomy unmasks its expression in heterozygotes

haploinsufficiency also causes inviability

81
Q

Euploidy

A

complete haploid sets (n) of chromosomes are present

individual has the correct number of chromosomes in them

82
Q

Polyploidy

A

several extra sets of chromosomes are present (several n)

common in plants, not animals

Associated with greater cell size

Naming of polyploids based on number of chromosomal sets; triploid is 3n

Autopolyploidy & allopolyploidy

83
Q

Odd-numbered polyploidy

A

Odd numbers of chromosome sets not usually maintained between generations

tripolyploid organisms don’t produce genetically balanced gametes, so they are sterile

84
Q

Autopolyploidy

A

addition of one or more extra sets of chromosomes, identical to normal haploid component of same species

often sterile

new polyploids can be induced using chemicals like colchicine

autotriploids & autotetraploids

85
Q

Colchicine

A

colchicine interferes with spindle formation, preventing migration to the poles

failure of cell division results in doubling of chromosome numbers

86
Q

Autotriploids & 3 causes

A

3n, Autopolyploidy

failure of chromosomes to segregate during meiosis, creating diploid gamete

fertilization of single egg by two sperm, creating triploid zygote

diploid + tetraploid = triploid (n + 2n = 3n)

sterility (3 homologs can’t properly pair in meiosis)

87
Q

Autotetraploids

A

4n, Autopolyploidy

arise by fusion of two diploid gametes

can be semifertile, as they produce balanced gametes; but their synapsis might produce univalents, trivalents, and quadrivalents, so good luck

88
Q

Allopolyploidy

A

combination of chromosome sets from different species, as a result of hybridization

use A and B to represent haploid set of chromosomes for two unrelated species

89
Q

Sterile hybrid in allopolyploidy

A

When the haploid gametes of 2 species fuse, a hybrid is created

for A of 2n=6 and B of 2n=4, AB has 5 chromosomes

this hybrid is sterile because there are no pairing partners

90
Q

Amphidiploid

A

allopolyploidy

Hybrid fertility can be restored by chromosomal doubling, a result of a cellular error (induced by chemicals like colchicine).

two diploid genomes combined = fertile allotetraploid

functionally diploid, forms bivalents during meiosis because every chromosome has one homologous partner

91
Q

Chromosomal breakage

A

Chromsomes can “break” due to exposure to chemicals or radiation

ends at the points of breaking are “sticky” and rejoin other broken ends

this results in a rearrangement of genetic information

92
Q

Heterozygous for the aberration

A

chromosomal rearrangement is found in one homolog, but not the other

unusual pairing formations found in meiotic synapsis

93
Q

Effect of being heterozygous for the aberration

A

if no loss of genetic information occurred, unlikely to be affected phenotypically

gametes may be duplicated or deficient for some chromosomal regions; OFFSPRING might show mutant phenotype

94
Q

Duplications & deletions

A

total amount of genetic information in chromosome changes

95
Q

Translocations & inversions

A

exchanges and transfers

locations of genes are altered within the genome

96
Q

Ratio of double recessive epistasis

A

9:7

97
Q

Deletion

A

Chromosome breaks; segment without centromere is lost

Compensation loop during meiosis; normal buckles

98
Q

Duplication & 3 consequences

A

any part of the genome is present more than once

may result in redundancy, phenotypic variation, and multigene families

99
Q

Terminal deletion

A

occurs near the end of chromosome

100
Q

Intercalary deletion

A

occurs in the chromosome’s interior

101
Q

Compensation loop

A

for synapsis between a deleted chromosome and its homolog, the normal chromosome must buckle out

for synapsis between a duplicated chromosome and its homolog, the duplicated chromosome must buckle out

102
Q

Gene redundancy

A

The presence of several genes in an organism’s genome that all have variations of the same function

caused by duplication

103
Q

Multigene families

A

groups of contiguous genes whose products perform the same or similar functions

come from an “ancestral” set of genes via duplication

104
Q

Copy number variation

A

duplications of portions of genes happen regularly; the number of copies in individuals differs

CNVs are important in the expression of many traits, including diseases

105
Q

Inversions

A

segment of chromosome is flipped

doesn’t involve loss of information, just rearranges the gene sequence

requires breaks at two points along length of chromosome, and reinsertion of inverted segment

if heterozygous, normal synapsis is not possible; inversion loop must be formed

106
Q

Paracentric inversion

A

centromere is not part of rearranged chromosome section

107
Q

Pericentric inversion

A

centromere is part of rearranged chromosome section

108
Q

Inversion heterozygotes

A

only have one inverted chromosome in a pair of homologs, such that during synapsis they must form an inversion loop

109
Q

Inversion loop & segregation

A

occurs in heterozygotes

if crossing over doesn’t occur within the inverted segment of the inversion loop, homologs segregate

if crossing over does, abnormal recombinant chromatids produced; each has some duplication and deletion; one is dicentric, the other acentric

110
Q

dicentric chromatid

A

recombinant chromatid produced from crossing over in a paracentric inversion

two centromeres

contains duplications and deletions

111
Q

dicentric chromatid behavior in meiosis

A

pulled in two directions, usually breaking; part of the chromatid goes in one gamete, and the rest into another

gametes containing these are deficient in genetic material

112
Q

acentric chromatid

A

recombinant chromatid produced from crossing over in a paracentric inversion

lacking a centromere

contains duplications and deletions

moves randomly to one pole during anaphase I, or might be lost; produces inviable gamete

113
Q

Evolutionary advantage of inversions

A

inversion heterozygotes suppress recombination among genes in the inverted region

sequence of alleles at adjacent loci are preserved

114
Q

Translocation

A

movement of chromosomal segment to new location

no genetic information lost or gained

115
Q

Reciprocal translocation

A

exchange of segments between non-homologous chromosomes

two nonhomologous chromosome arms exchange at break points

116
Q

Heterozygous for a reciprocal translocation in meiosis

A

“crucifix” shaped pairing of homologs

4 chromosomes involved, including unaffected homologs, and both translocated chromosomes

produces half genetically unbalanced gametes (semisterility)

117
Q

Alternate segregation

A

normals move to one pole, translocated to another

produce viable gametes; both possess one complete set of the chromosome segments

118
Q

Adjacent segregation

A

for chromosomes 1 and 2, where N is normal and T is translocated

N1 and T2 move towards one pole, N2 and T1 move towards another

produce nonviable gametes containing duplications and deficiencies

119
Q

Semisterility

A

half of the gametes from someone heterozygous for reciprocal translocation are viable

120
Q

Roberstonian translocations

A

chromosomal breaks occur near centromeres

fragments containing centromeres rejoin

generates one large chromosome and one small acentric chromosome, which is lost

chromosome number is reduced

121
Q

Familial down syndrome

A

long arm of 21 and short arm of 14 swap

large chromosome of two long arms, short chromosome lost

people with the translocation are called ‘carriers’; phenotypically normal, but increased chance of producing abnormal children, as their gametes may segregate in Strange Ways

122
Q

Familial down syndrome gamete segregation

A

STYLE 1:
half of the gametes will have N21 and N14; normal offspring
half of the gametes will have T14+21; carrier

STYLE 2:
half of the gametes will have N21 and T14+21, aka 2 copies of 21 information; down syndrome
half of the gametes will have N14 and no 21; aborted

123
Q

Fragile sites

A

unstable chromosome regions prone to breakage

one is on the X chromosome, associated with mental retardation

results from an increase in # of repeats of CGG

124
Q

Incomplete Dominance notation

A

denoted with superscripts attached to uppercase letters

125
Q

Doubling

A

The restoration of fertility in sterile allopolyploid plants; the chromosome number doubles such that the plant is now amphidiploid.

126
Q

Cause of duplication

A

arise as the result of unequal crossing over during prophase I

127
Q

Pericentric inversion loop crossing over

A

The two chromatids involved in the crossing over will contain duplications and deletions, making them inviable for gametes; but they aren’t di- or acentric

128
Q

Nondisjunction

A

the failure of homologous chromosomes or sister chromatids to separate during cell division

creates aneuploidy

Biol251 (8 decks)

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