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
X-linkage
mutations attached to the x chromosome results in unique patterns of inheritance, dependant on sex
26
Hemizygous
males cannot be homo/heterozygous for x-linked genes express whatever's on their single X
27
Crisscross pattern of inheritance
traits controlled by x-linkage are passed from homozygous mothers to all sons
28
sex-limited inheritance
A trait that is expressed in one sex, even though the trait is not X- or Y-linked
29
sex-influenced inheritance
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
30
Degree of expression
some mutant genotypes produce individuals whose phenotypes are essentially normal; extent of mutation's presence is measured in penetrance and expressivity
31
penetrance
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)
32
Expressivity
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
33
conditional mutations
phenotypic expression is determined by environmental conditions
34
temperature-sensitive mutations
conditional mutation that produces a mutant phenotype at a given temperature i.e, enzyme only active in warmer temperatures; enzyme affects phenotype
35
Permissive condition
the condition where the conditional mutation is shown
36
Restrictive conditions
conditions under which the conditional mutation does not show
37
Genetic anticipation
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
38
Ratio of recessive epistasis
9:4:3
39
Ratio of dominant epistasis
12:3:1
40
Double recessive epistasis
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
41
Heterogametic sex
Unlike gametes; ZW, XY, X0 always determines sex of progeny Male not always heterogametic
42
Homogametic sex
Like gametes, XX, ZZ
43
Klinefelter
XXY
44
Turner
X
45
Reciprocal translocation on sex chromosomes
Causes XY to develop female and XX male SRY mutation; SRY jumps from Y to X or vice versa
46
Physical process of sex differentiation
1. embryo hermaphroditic early in development 2. bipotential gonadal ridges appear, sexually indeterminate 3. gonadal ridges differentiate into testes with Y chromosome present
47
Bipotential gonads
Undifferentiated gonadal ridges early in development
48
PAR
Pseudoautosomal region of Y chromosome; shares homology with X, pairs during meiosis
49
Male-specific region of Y
divided equally between euchromatin and heterochromatin; doesn't pair during meiosis contains SRY
50
SRY
Sex-determining region of Y gene region that controls male development encodes for TDF
51
TDF
testis-determining factor causes testicular formation; encoded by SRY
52
Primary sex ratio
ratio of sex at conception; equal amounts of female and embryos conceived; more XX die during development
53
Secondary sex ratio
Sex at birth; more XY than XX born
54
Dosage compensation
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
Barr body
an inactivated X chromosome all but 1 X will become a Barr body not all genes on Barr body are inactivated; Xic
56
Lyon hypothesis
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
Lyonization
Random inactivation of an X chromosome
58
Xic
X inactivation center major control unit of X chromosome; expressed only on inactivated X has a gene XIST which is critical for inactivation
59
Imprinting
the same X chromosomes are inactive in subsequent divisions one or both chromatin components are chemically modified, silencing them Forever
60
Drosophila sex determination system
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
Location of sex-related genes in drosophila
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
Metafemales
many X chromosomes, such that X:A ratio exceeds 1:1 weak and sterile
63
Intersex drosophila
0.5 < X:A < 1.0 (between standard male and standard female)
64
Metamales
X:A ratio is less than 0.5, more autosomes than X weak and sterile
65
Genetic basis of Drosophila sex differentiation
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
SXL
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
TRA
transformer if Sxl present, produces female TRA protein if no Sxl present, no TRA protein made this protein influences expression of dsx
68
dsx
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
dsxm
male DSX proteins represses genes required for female development, activates male specific genes
70
Drosophila dosage compensation
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
DCC
dosage compensation complex; creates gene-activating proteins will activate male X-linked genes more often, to give an equivalent dosage
72
Temperature dependent sex determination
steroids affected by temperature are important in sex determination in these systems
73
Aromatase
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
Interplay of genetic and temp differentiation systems
animals can have XX/XY chromosomes, but during development can be converted between sexes at different temperatures
75
Chromosome mutations
changes in total # of chromosomes deletion or duplication of segments of chromosomes rearrangement of chromosomes
76
Aneuploidy
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
Monosomy
Type of aneuploidy loss of a single chromosome from an otherwise diploid genome; 2n-1 usually not tolerated for autosomes
78
Haploinsufficiency
a single copy of a recessive gene due to monosomy may be insufficient to provide life-sustaining function
79
Trisomy
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
2 complications of monosomy
if just one gene on an inherited chromosome is a lethal allele, monosomy unmasks its expression in heterozygotes haploinsufficiency also causes inviability
81
Euploidy
complete haploid sets (n) of chromosomes are present individual has the correct number of chromosomes in them
82
Polyploidy
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
Odd-numbered polyploidy
Odd numbers of chromosome sets not usually maintained between generations tripolyploid organisms don't produce genetically balanced gametes, so they are sterile
84
Autopolyploidy
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
Colchicine
colchicine interferes with spindle formation, preventing migration to the poles failure of cell division results in doubling of chromosome numbers
86
Autotriploids & 3 causes
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
Autotetraploids
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
Allopolyploidy
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
Sterile hybrid in allopolyploidy
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
Amphidiploid
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
Chromosomal breakage
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
Heterozygous for the aberration
chromosomal rearrangement is found in one homolog, but not the other unusual pairing formations found in meiotic synapsis
93
Effect of being heterozygous for the aberration
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
Duplications & deletions
total amount of genetic information in chromosome changes
95
Translocations & inversions
exchanges and transfers locations of genes are altered within the genome
96
Ratio of double recessive epistasis
9:7
97
Deletion
Chromosome breaks; segment without centromere is lost Compensation loop during meiosis; normal buckles
98
Duplication & 3 consequences
any part of the genome is present more than once may result in redundancy, phenotypic variation, and multigene families
99
Terminal deletion
occurs near the end of chromosome
100
Intercalary deletion
occurs in the chromosome's interior
101
Compensation loop
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
Gene redundancy
The presence of several genes in an organism's genome that all have variations of the same function caused by duplication
103
Multigene families
groups of contiguous genes whose products perform the same or similar functions come from an "ancestral" set of genes via duplication
104
Copy number variation
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
Inversions
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
Paracentric inversion
centromere is not part of rearranged chromosome section
107
Pericentric inversion
centromere is part of rearranged chromosome section
108
Inversion heterozygotes
only have one inverted chromosome in a pair of homologs, such that during synapsis they must form an inversion loop
109
Inversion loop & segregation
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
dicentric chromatid
recombinant chromatid produced from crossing over in a paracentric inversion two centromeres contains duplications and deletions
111
dicentric chromatid behavior in meiosis
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
acentric chromatid
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
Evolutionary advantage of inversions
inversion heterozygotes suppress recombination among genes in the inverted region sequence of alleles at adjacent loci are preserved
114
Translocation
movement of chromosomal segment to new location no genetic information lost or gained
115
Reciprocal translocation
exchange of segments between non-homologous chromosomes two nonhomologous chromosome arms exchange at break points
116
Heterozygous for a reciprocal translocation in meiosis
"crucifix" shaped pairing of homologs 4 chromosomes involved, including unaffected homologs, and both translocated chromosomes produces half genetically unbalanced gametes (semisterility)
117
Alternate segregation
normals move to one pole, translocated to another produce viable gametes; both possess one complete set of the chromosome segments
118
Adjacent segregation
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
Semisterility
half of the gametes from someone heterozygous for reciprocal translocation are viable
120
Roberstonian translocations
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
Familial down syndrome
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
Familial down syndrome gamete segregation
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
Fragile sites
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
Incomplete Dominance notation
denoted with superscripts attached to uppercase letters
125
Doubling
The restoration of fertility in sterile allopolyploid plants; the chromosome number doubles such that the plant is now amphidiploid.
126
Cause of duplication
arise as the result of unequal crossing over during prophase I
127
Pericentric inversion loop crossing over
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
Nondisjunction
the failure of homologous chromosomes or sister chromatids to separate during cell division creates aneuploidy