test 4 Flashcards Preview

genetics > test 4 > Flashcards

Flashcards in test 4 Deck (98):
1

mutation

any permanent change to the genetic material

2

epigenetic changes

non-permanent changes to genetic material (like methylation of DNA bases)

3

classified according to:

origin of mutation
site of mutation
chromosome vs. gene mutation

4

origin of mutation

spontaneous mutations
induced mutations and mutagens

5

spontaneous mutations

mutations that occur naturally but at very low rate

6

induced mutations

mutations induced by various outside factors called mutagens
chemical mutagens and mutagenic radiation

7

chemical mutagens

numerous chemicals can alter DNA by reacting with it or creating other molecules that react with DNA

8

mutagenic radiation

ionizing radiation
ultraviolet radiation

9

ionizing radiation

radiation that creates radicals or ion pairs as it passes through tissue (very reactive and can modify DNA))
ex: x-rays, gamma, alpha, and beta particles, neutrons

10

ultraviolet radiation

some UV can cause ionization but it is usually mutagenic due to its ability to create covalent bonds between adjacent thymine bases in DNA (thymine dimers)

11

site of mutation

germ-line mutations
somatic mutations

12

germ-line mutations

mutations in gametes or cells destined to become gametes
can be passed on to future generations

13

somatic mutations

mutations in somatic cells and can't be passed along
carcinogenesis and mutagenesis: class of mutations in which normal gene turned into cancer gene (oncogene)

14

chromosome mutation

mutations that change the chromosome number or chromosome structure but may not have a detectable effect on individual genes
instead dosage or locus of gene is changed

15

change in chromosome number

euploidy
aneuploidy and nondisjunction
aneuploidy of sex chromosomes

16

euploidy

addition/subtraction of whole haploid set
haploidy/monoploidy
polyploidy

17

haploidy/monoploidy

1n condition in organism that is normally 2n
very rare

18

polyploidy

autopolyploidy
allopolyploidy

19

autopolyploidy

gaining of duplicate genomes from same species

20

allopolyploidy

polyploidy by adding genomes of different species

21

aneupolyploidy and nondisjunction

gaining/losing single (or several) chromosomes
main cause of spontaneous abortions and mental retardation
extremely common in cancer tumors
often occurs by mistake of meiosis called nondisjunction (anaphase I) when chromosomes fail to separate
ex. trisomy, monosomy, and aneuploidy of sex chromosomes

22

trisomy

individual who has gained chromosome
down syndrome (trisomy 21): caused by nondisjunction in oogenesis
trisomy 18 and 13 also common

23

monosomy

loss of single chromosome

24

aneuploidy of sex chromosomes

klinefelter syndrome: male with more than 1 X (XXY)
turner syndrome: XO female (female missing part of 1 X chromosome)

25

changes in chromosome structure

duplication
deletions
inversions
translocations

26

duplication

segment that is duplicated (in 1 of 3 configurations)
1. tandem duplications
2. palindromes
3. displace duplications

27

tandem duplication

have duplicated segment in original order and next to it
can be due to unequal crossing over (homologous and nonhomologous)

28

homologous unequal crossing over

secondary event that occurs as result of presence of previous tandem duplication

29

nonhomologous unequal crossing over

original event that creates tandem duplication and deletion

30

palindromes

repeat that is in reverse order compared to the original segment

31

displace duplications

duplication in which duplicated segment is not adjacent to original segment

32

human duplications

Hb Lepore syndrome
huntington disease
fragile-x syndrome

33

Hb Lepore syndrome

normal adult hemoglobin has 2 alpha and 2 beta globins but this syndrome results when individual has 1 mutant Lepore beta Hb allele and 1 normal beta allele
heterozygotes for Lepore beta Hb usually asymptomatic
homozygotes for Lepore beta Hb have severe anemia
most likely from homologous unequal crossing over

34

huntington disease

due to trinucleotide repeat which encodes multiple glutamines
normal number of repeats between 9-36
people with 36-39 repeats show reduced pentrance
affected individuals have 60+ repeats

35

fragile-x syndrome

x-linked dominant disorder
also involves extra copies of trinucleotide repeat

36

deletions

like tandem duplications they can also be caused by unequal crossing over
single/multiple chromosomes deleted

37

inversions

reversal of the orientation of a segment of a chromosome
may be paracentric or pericentric
inversion heterozygotes have trouble making functional gametes due to crossing over in inverted segment

38

translocations

move a segment to a non-homologous chromosome
also have reduced fertility
robertsonian translocation

39

robertsonian translocation

nonhomologous exchange between 2 acrocentric or telocentric chromosomes that ca result in fused (metacentric) chromosome

40

chemical nature of the change to the DNA molecule

base substitutions (point mutations)
base insertions and deletions and indels

41

base substitutions (point mutations)

substitution of 1 base for another
if not corrected it will become a base-pair substitution
transitions: purine substituted for purine and pyrimidine for pyrimidine
transversions: purine substituted for pyrimidine and pyrimidine for purine

42

SNPs

single nucleotide polymorphisms
marker point mutations that have been mapped across human genome and are useful in hunting for unknown genes

43

base insertions and deletions and indels

error of replication may add or skip nucleotide or several nucleotides (small indels)

44

causes of chemical changes to DNA molecule

replication errors and slippage
tautomeric shifts
chemical modification of bases
intercalation
base analogs
ionizing radiation
UV light
transposons

45

replication errors and slippage

DNA polymerase can make various errors resulting in base substitution or insertions and deletions
slippage occurs when DNA polymerase slips over base pair or stutters and puts in extra nucleotide

46

tautomeric shifts

if rare tautomer of base is present during replication, it can result in a base substitution
keto-->enol
amino-->imino

47

chemical modification of bases

depurination: some agents (like water) cause the removal of a purine
deamination: an amino group may be removed from base
oxidation: oxygen may be added to base
alkylation: alkyl group added to base by alkylation

48

intercalation

some chemicals can slip right between adjacent bases causing trouble during DNA replication

49

base analogs

some chemicals are so similar to natural bases that they can be incorporated in place of one of the normal bases

50

ionizing radiation

can create reactive ion pairs which in turn react with DNA to chemically modify it
x-rays in particular cause DNA single-strand and double-strand breaks

51

UV light

UV changes DNA by creating covalent bonds (thymine dimers) between 2 thymines that line in sequence on a DNA strand

52

transposons

mobile genetic elements can insert a short DNA sequence in the DNA

53

effects of mutations on protein synthesis

missense mutation
same sense mutation (synonymous mutation, silent mutation)
nonsense mutation
frameshift mutation

54

missense mutation

base substitution that results in one amino acid of the polypeptide being changed
ex. sickle cell anemia

55

same sense mutation (synonymous mutation, silent mutation)

base substitution that results in no change in the polypeptide

56

nonsense mutation

base substitution that results in premature termination of the translation of a polypeptide

57

frameshift mutation

insertion or deletion of a nucleotide causes a shift in the reading frame and changes many amino acids of the polypeptide

58

genetically determined sex

single-gene systems
euploid systems

59

single-gene systems

in some organisms a single gene determines the mating type

60

euploid systems

in some organisms sex is determined by the ploidy of the individual
ex: if queen honey bee's eggs are fertilized (2N) they become females but if not they develop parthenogenetically into males (1N)
queen eats royal jelly and becomes fertile

61

sex chromosomes

many animals and some plants have a sex-chromosome mechanisms for sex determination\
XY and XO systems

62

XY and XO systems

female is homogametic and the male is heterogametic
balance theory of sex determination
Y determination in mammals

63

balance theory of sex determination

in drosophilia sex is determined by the ratio of X chromosome sets to autosome sets but the Y is necessary for fertility
X/A >= 1 : female
X/A <= 0.5 : male

64

Y determination in mammals

sex determined by presence or absence of Y chromosome
Y chromosome present (SRY on Y present) = male
no Y chromosome present = female
SRY must be present on Y to be male bc it codes for protein testis-determining factor (TDF) which causes embryonic changes which result in undifferentiated future gonad to develop into a testis

65

ZW systems

birds, moths, butterflies, and some others the male is homogametic (ZZ) and the female is heterogametic (ZW)

66

dosage compensation

since XX females have 1 more X chromosome than males there is a mechanism to equalize the dose of X-linked genes between males and females
lyonization and other mechanisms

67

lyonization

X-inactivation
in mammals dosage compensation accomplish by the random inactivation of 1 X chromosome early in development
can be seen as Barr Body in females (inactive X)

68

other dosage compensation mechanisms

in drosophilia Sxl gene involved in sex determination causes increases transcription of the genes on the single X of males so that it is the same as that on the 2 Xs of females

69

sex linked traits

involves genes on a sex chromosome

70

sex limited traits

involves autosomal genes expressed genes that are only expressed on 1 sex

71

sex influenced traits

involves autosomal genes that are expressed when heterozygous in 1 sex but not in the other sex

72

how does recombination occur at the DNA level

formation of Holliday Junction intermediate with region of heteroduplex
resolution of junction by endonuclease nicking can result in a crossover but alternate resolution can result in molecule with heteroduplex but no crossover

73

eukaryotic recombination

Holliday junction as described before

74

prokaryotic recombination

bacteria may exchange genes by various methods
conjugation
Hfr conjugation
sexduction
other plasmids

75

conjugation

F+ (male) E.Coli are capable of transferring genetic material to F- cells
F+ cells have small episome (plasmid) called an F factor which has no genes essential for survival
F- cells lack F factor
F+ cells extend conjugation tubes through which they transfer F factor to F- cells turning them into F+ cells
replication of F factor occurs as it is being transferred

76

Hfr conjugation

if F factor becomes integrated into the bacterial chromosome then these Hfr cells attempt to transfer the entire chromosome into an F- cell
since F factor is the last part to be transferred the recipient cells don't become male but receives DNA from the Hfr cell
this DNA can then recombine with its own DNA resulting in a new genotype

77

sexduction

sometimes the F factor excises from the chromosome and takes a piece of the chromosome with it to form an F factor
transfer of an F factor creates a merozyote (partially diploid cell) also called merodiploid cell

78

other plasmids

R factors have genes that convey antibiotic resistance and may be transferred thus spreading the resistance genss

79

organelle genetics

2 separate genetic systems involved in the production of mitochondria and chloroplasts
nuclear system
organelle system

80

nuclear system

most proteins found in mitochondria and chloroplasts are coded for by nuclear genes, made on cytoplasmic ribosomes, then transported into mitochondria

81

organelle systems

some proteins in these organelles are coded for by organelle DNA and made on organelle ribosomes

82

organelle genomes

mitochondria and chloroplasts have their own small DNA molecules that are usually circular and are present in multiple copies
mitochondrial dna (mtDNA)
chloroplast dna (ctDNA or cpDNA)

83

mitochondrial dna

animal 16-19 kb long
replication begins from D-loop regions and replicates one strand, then when reaching the D-loop again, the other strand is replicated in the opposite direction
codes for tRNA and rRNA and a few proteins
2 promoters on heavy strand and 1 promoter on light strand
makes 3 RNA: rRNA (2), tRNA (22), and mRNA
use genetic code slightly different from nuclear code

84

chloroplast dna

plant 120-180 kb long
may be circular or linear

85

organelle division

mitochondria and chloroplasts are never made de novo but always come from pre-existing organelles
DNA replication occurs throughout the cell cycle
organelle division occurs by furrowing of the inner membrane with DNA molecules being distributed between the daughter organelles

86

organellar inheritance

inheritance of mitochondrial and chloroplast genes is non-mendelian
in yeast this leads to random segregation of traits
in higher organisms seen as maternal inheritance since mitochondria and chloroplast are usually inherited via the ovum only

87

other extranuclear genes

endosymbionts like kappa (killer) in paramecium

88

human mitochondrial traits

many are lethal and only seen in heteroplasmy (some normal mitochondria present)

89

gene technology

era of gene technology began in 1970s
restriction enzymes (restriction endonucleases)
gel electrophoresis
shotgun and other cloning methodologies
PCR
DNA sequencing

90

restriction enzymes

endonucleases that recognize certainpalindromic DNA sequences and cut the molecule there

91

gel electrophoresis

technique used to separate DNA molecules according to size
used after restriction enzymes

92

shotgun and other cloning methodologies

early cloning experiments placed random foreign DNA segment (from using restriction enzymes to ligate target DNA) in plasmid then placed that plasmid in E. Coli
subsequent cloning experiments placed DNA copy of eukaryotic mRNA (cDNA)(gene minus introns) into E. COli
this methodology led to creating bacteria that could produce human proteins like insulin
cloning procedures like this can be used to build genomic libraries or cDNA libraries

93

PCR

in vitro methodology that amplifies a segment of DNA 2^30 fold

94

DNA sequencing

early sequencing methods used radioactive labels
sanger sequencing determines sequence of segment of DNA a few hundred up to a thousand bp in length
next-generation sequencing greatly increases the quantity of DNA that can be sequenced

95

human genome project

mega-sequencing project undertaken at end of last century had goal of sequencing a 3 billion base-pair human genome

96

microarrays

gene chips
1 of many methodologies used in genomics
relies on hybridization of DNA or RNA extracted from an organism to DNA molecules that are fixed on a gene chip
1 use is to determine which genes out of 20000+ genes are transcribed in specific human tissue

97

gene knockdown using RNAi

RNA interference (RNAi) can suppress translation of 1 specific mRNA
can be used to study what effect of reducing expression of a specific gene is (which shows what possible function of gene is)

98

CRISPR/Cas9

systems that can be programmed to target specific stretches of genetic code and to edit DNA at precise locations
researchers can permanently modify genes in living cells and organisms and, in the future, may make it possible to correct mutations at precise locations in the human genome in order to treat genetic causes of disease