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DAT > ch. 5 genetics > Flashcards

ch. 5 genetics Flashcards

1
Q

heredity

A

the genetic passing of characteristics from one generation to another

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2
Q

gene

A

genetic material on a chromosome for encoding a trait

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3
Q

locus

A

location on chromosome where a gene is located

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4
Q

allele

A

alternative forms of a gene that allow for differences such as different hair or fur colors

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5
Q

homologous chromosomes

A

a pair of chromosomes that contain the same genetic material

  • each parent contributes one of the chromosomes in the pair, thus allowing for different alleles to be present for each gene
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6
Q

law of segregation

A

one member if each chromosome pair migrates to an opposite pole in anaphase I so that each gamete is haploid
i. each gamete is left with one copy of each allele

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7
Q

law of independent assortment

A

the migration of homologues within one pair of homologous chromosomes does not influence the migration of homologues of other homologous pairs

they separate randomly

independent assortment can be observed in a dihybrid cross of peas- the presence of new phenotype combinations indicates the genes for seed shape and color assort independently

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8
Q

gregor mandel

A

discovered the basic principles of heredity through extensive experiments with pea plants

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9
Q

monohybrid cross

A

two organisms with variations at one gene of interest are crossed

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10
Q

dihybrid cross

A

two organisms with variations at two genes of interest on different chromosomes are crossed

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11
Q

test cross

A

when the genotype of an organism expressing the dominant phenotype is unknown, the unknown organism is crossed with a homozygous recessive organism to determine if the unknown is homozygous dominant or heterozygous dominant

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12
Q

punnett squares

A

uses probability rules to determine the outcomes of either monohybrid or dihybrid crosses and the subsequent expected frequencies

genotypes of mother and father are listed outside the box

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13
Q

incomplete dominance

A

blending of expression of alleles

ex) a red flower and white flower are cross to give a heterozygous pink offspring

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14
Q

codominance

A

both of the inherited alleles are completely expressed

ex) blood types A and B can show as AB if both are expressed

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15
Q

multiple alleles

A

blood groups have four possible phenotypes, the codominant A, B, and O, leading to six possible genotypes and four possible phenotypes

i. AA/AO –> type A
ii. BB/BO –> type B
iii. AB –> codominant AB type
iv. AB –> codominant AB type
v. OO –> type O

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16
Q

epistasis

A

the process in which one gene affects the phenotypic expression of a second gene

ex) one gene controls the production of pigment by either turning on or turning off, and the second gene controls the color or amount of color in the fur. Therefore, if the first gene codes for no pigment, then the second gene has no effect

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17
Q

pleiotropy

A

when a single gene has more than one phenotypic expression

ex) gene in pea plants that expresses for seed texture, but also influences the phenotype of starch metabolism and water uptake
ex) a mutation in the single gene responsible for sickle cell anemia can result in the expression of multiple different health conditions: pain, stoke, high blood pressure

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18
Q

polygenic inheritance

A

the interaction of many genes to shape a single phenotype with continuous variation such as height, skin color, or hair color

many genes work together to create one effect

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19
Q

linked genes

A

when two or more genes reside physically close to one another on the same chromosome and therefore cannot separate independently as they are inherited together

  • genes that are unlinked have a 50% change of recombination. the lower the % of recombination, the closer the genes are
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20
Q

sex-linked genes

A

a type of linked gene that refers to a single gene residing on a sex chromosome that is inherited differently in males and females

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21
Q

sex-influenced genes

A

the expression of genes can be influenced by the sex of the individual carrying the trait

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22
Q

penetrance

A

probability of an organism with a specific genotype will express a particular phenotype

i. complete penetrance - the genes for a trait are expressed in all of the population who have the gene
ii. incomplete penetrance - the genes for a trait are only expressed in a percentage of the population

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23
Q

variable expressivity

A

the variation or range of phenotypes for a specific genotype

ex) the gene for red hair could result in light hair, dark crimson hair, or any range of color

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24
Q

X-inactivation

A

during embryonic development in female mammals, one of the two inherited X chromosomes does not uncoil into chromatin, and remains as a dark and coiled compact body, which is referred to as a Barr body. Barr bodies are therefore not expressed, and only the genes on the other X chromosome that did uncoil are expressed

ex) in Calico cats, where the characteristic black and orange fur coat depends on which copy of the X chromosome the cell chooses to leave active

  • a genetic disease that can result from this is hemophilia, a recessive condition which results in the inability to form blood clots.
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25
Q

nondisjunction

A

when one or more chromosome pairs or chromatids fail to separate during mitosis. this commonly occurs during anaphase of mitosis, when two chromatids of a single chromosome fail to separate, or during anaphase of meiosis.

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26
Q

mosaicism

A

a phenomenon that occurs in cells that undergo nondisjunction in mitosis during embryonic development; fraction of body cells have extra or missing chromosomes

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27
Q

polyploidy

A

when all chromosomes undergo meiotic nondisjunction and produce gametes with twice the number of chromosomes
a. is common in plants

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28
Q

point mutation

A

a single nucleotide change causing either substitution, insertion, or deletion - the latter two can cause a frameshift mutation

transition mutation - conversion of a purine to purine/pyrimidine to pyrimidine
transversion mutation - conversion of a purine to pyrimidine or vice versa

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29
Q

aneuploidy

A

a genome with extra or missing chromosomes, often caused by nondisjunction
i. Down syndrome, or trisomy 21
ii. turner syndrome is a genetic condition in which a female is either completely missing, or partly missing an X chromosome, leading to the genotype XO.
iii. Klinefelter’s syndrome - male is born with an extra X chromosome

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30
Q

chromosomal aberrations

A

chromosome segments are changed

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31
Q

duplications

A

chromosome segments are repeated on the same chromosome, which can occur from unequal crossing over

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32
Q

inversions

A

chromosome segments are rearranged in reverse orientation

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33
Q

translocations

A

one segment of a chromosome is moved to another chromosome

a) can be reciprocal ( two non-homologous chromosomes swap segments) or Robertsonian (one chromosome from a homologous pair becomes attached to another chromosome from a different pair)

ex) an extra 21 chromosome attached to chromosome 14 can cause Down syndrome as well, due to the tripled 21 chromosome segment

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34
Q

chromosomal breakage

A

spontaneous or induced breakage of a chromosomal segment via mutagenic agents or X-rays

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35
Q

mutagenic agents

A

include cosmic rays, X-rays, UV rays, radioactivity, chemical compounds including colchicine and mustard gas that can cause genetic mutations. generally also carcinogenic

i. colchicine functions by inhibiting spindle formation, which can cause polyploidy

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36
Q

phenylketonuria (PKU)

A

autosomal recessive condition

the inability to produce the proper enzyme for phenylalanine breakdown, causing degradation product phenylpyruvic acid to accumulate

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37
Q

cystic fibrosis

A

autosomal recessive condition

fluid buildup in respiratory tracts

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38
Q

tay-sachs

A

autosomal recessive condition

lysosome defect in which cells can’t breakdown lipids for normal brain function

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39
Q

huntington’s disease

A

autosomal dominant condition

nervous system degeneration

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40
Q

achondroplasia

A

autosomal dominant condition

causes dwarfism

41
Q

hypercholesterolemia

A

autosomal dominant condition

excess cholesterol in blood that progresses into heart disease

42
Q

hemophilia

A

sex-linked recessive condition

causing abnormal blood clotting

43
Q

color blindness

A

sex-linked recessive condition

primarily observed in males

44
Q

duchenne’s muscular dystrophy

A

sex-linked recessive condition

progressive loss of muscle

45
Q

Down’s syndrome

A

trisomy 21

46
Q

Turner’s syndrome

A

deletion of X chromosome –> XO genotype

47
Q

Klinefelter’s syndrome

A

extra X chromosome –> XXY genotype

48
Q

Cri du Chat

A

deletion on chromosome 5

49
Q

a fetus can be tested for genetic disorders via ______

A

amniocentesis or chorionic villus sampling (CVS)

50
Q

extranuclear inheritance

A

extranuclear genes (genes present in organelles other than the nucleus) are found in mitochondria and chloroplasts

i. defects in mitochondrial DNA can reduce a cell’s ATP production, and because mitochondrial DNA is inherited only from the mother, all related mitochondrial defects/diseases are also inherited

51
Q

patterns of inheritance

A

homozygous - two copies of the same allele are inherited
heterozygous - different alleles of the same gene are inherited
hemizygous - one single copy of a gene is inherited instead of two (ex: males)

52
Q

lethal gene

A

if the recessive is lethal, for example, don’t include it in the ratio of genotypes

if a phenotype skips generations, be suspicious of an autosomal recessive disorder. if no skip, it is most likely an autosomal dominant disorder. be suspicious for X-linked recessive if a father doesn’t have the phenotypes and none of his daughters display it

53
Q

DNA backbone

A

5’ to 3’ phosphodiester bonds to form a sugar-phosphate backbone

54
Q

steps of DNA replication

A
  1. a second chromatid containing a copy of DNA is assembled during interphase
    -DNA is replicated via semiconservative
    replication, where one strand is always old
    and one strand is always new
  2. helicase unwinds the DNA, forming a replication fork
    • single stranded binding proteins attach to
      each strand of uncoiled DNA to keep them
      separate
    • topoisomerases break and rejoin the
      DNA double helix, preventing knots
  3. DNA polymerase moves from the 3’ to 5’ direction only, and synthesizes a new strand that is antiparallel (5’ to 3’)
    • the DNA polymerase has to go back to
      the replication fork and work away from it,
      producing Okazaki fragments
    • DNA ligase connects these fragments
  4. Primase creates a small strip of RNA
    • DNA polymerase I replaces base pairs
      form the RNA primers and functions in
      DNA repair
    • DNA polymerase III is mainly for
      replication
  5. Ligase glues two strands of DNA together
55
Q

the three stop codons

A

UAA, UAG, and UGA which do not code for any amino acids

56
Q

tRNA

A

a clover shaped transporter of anticodons

one end attaches to the amino acid being transported, and the other end is the anticodon which base pairs with the codon in mRNA

Wobbles: the exact base pair of the third nucleotide in the codon is often not required, allowing 45 different tRNA’s to base-pair with 61 codons that code for amino acids

the clover shape is held together by hydrogen bonds

smallest RNA molecule

57
Q

rRNA

A

form ribosomes

  • a ribosome has four total binding sites
    • one for mRNA
    • three for tRNA
      P site: carries the growing polypeptide chain
      A site: 2nd tRNA that delivers the next amino acid
      E site: for the empty tRNA before leaving the ribosome

note: the ribosome is assembled in nucleolus but the large and small subunits are exported separately to the cytoplasm

58
Q

steps for transcription

A
  1. initiation - RNA polymerase attaches to the promoter region on DNA and unzips the DNA into 2 strands. Promoter region for mRNA transcription often contains TATA
  2. elongation - RNA polymerase continues unzipping DNA and assembles RNA nucleotides using one strand of DNA as a template. Only one strand is transcribed, from the template = (-) antisense strand, while the other is the coding (+) sense strand for protection against degradation
  3. termination - occurs when RNA polymerase reaches a special sequence, often AAAAAA in eukaryotes
59
Q

before leaving the nucleus, pre-mRNA undergoes several modifications:

A
  1. 5’ cap (5’ G-P-P-P): this sequence is added the the 5’ end of the ,=mRNA; a guanine with three phosphate groups (GTP) provides stability for mRNA and a point of attachment for ribosomes
  2. A poly-A tail (-A-A-A…A-A-3’): this sequence is attached to the 3’ end of the mRNA. the poly A tail consists of 200 A nucleotides that serve to provide stability and control the movement of mRNA across the nuclear envelope
  3. RNA splicing : removes nucleotide segments from mRNA before mRNA moves into the cytoplasm via small nuclear ribonucleoproteins (snRNP’s). the spliceosome deletes the introns and splices the exons
  4. alternative splicing: allows different mRNA to be generated from the same RNA transcript by selectively removing differences of an RNA transcript into different combinations
60
Q

translation steps

A
  1. initiation: the small ribosome subunit attaches to the 5’ end of the mRNA; a tRNA methionine attaches to the start sequence of mRNA (AUG), and the large ribosomal subunit attaches to form a compete complex. requires 1 GTP
  2. elongation: next tRNA binds to the A site, peptide bond formation occurs, and the tRNA without methionine is released. the tRNA currently in the A site moves to the P site (translocation) and the next tRNA comes into the A site to repeat the process. this requires 2 GTP per link
  3. termination: when the ribosome encounters the stop codon (either UAG, UAA, or UGA), the polypeptide and the two ribosomal subunits all release due to a release factor breaking down the bond between tRNA and the final amino acid of the polypeptide
    i. while the polypeptide is being translated,
    amino acid sequences are determining the
    folding conformation, which is a process
    that requires assistance from chaperone
    proteins and 1 GTP
  4. post-translation: translation begins on a free floating ribosome; a signal peptide at the beginning of the translated polypeptide may direct the ribosome to attach to the ER, in which case the polypeptide is injected into the ER lumen. if injected, the polypeptide may be secreted from the cell via the Golgi apparatus
61
Q

amino acids for start codons in eukaryotes vs. bacteria

A

methionine vs. n-formylmethionine

62
Q

redundancy or degeneracy

A

most amino acids have more than one codon specifying them

63
Q

silent mutations

A

when a mutation occurs, but the new codon still codes for the same amino acid, therefore the effect is silenced

64
Q

nonsense mutations

A

the new codon codes for a stop codon

65
Q

neutral mutations

A

there is no change in protein function

66
Q

missense mutations

A

a new codon codes for a new amino acid —> can have a minor or fatal results (as in sickle cell anemia where glu–>val)

67
Q

proofreading

A

DNA polymerase checks base pairs

68
Q

mismatch repair

A

enzymes repair the errors DNA polymerase missed - mismatch repair deals with correcting mismatches between normal bases

69
Q

excision repair

A

enzymes remove nucleotides damaged by mutagens

70
Q

nucleotide excision repair

A

can be used to repair tissues like thymine dimers

71
Q

base excision repair

A

similar in function to nucleotide excision repair, but uses different enzymes. the main difference is that nucleotide excision will chunk out an entire segment around the faulty base by nicking the entire surrounding phosphodiester backbone, not just the faulty base

base excision repair first chunks out just the faulty base, then the phosphodiester backbone around the base is cut out, then polymerase I does some 5’ to 3’ exonuclease cutting and fills in the gaps

72
Q

nucleosome

A

structure formed when DNA is coiled around bundles of 8-9 histone proteins, kind of like beads on a string

during cell division (interphase), however, chromatin exists as two types:

  1. euchromatin: chromatin is loosely bound to nucleosomes; present when DNA is actively being transcribed
  2. heterochromatin: areas of tightly packed nucleosomes where DNA is inactive and appears darker. contains satellite DNA
73
Q

transposons (jumping genes)

A

DNA segments that can move to a new location on either the same or different chromosome

two types:
1. insertion sequences that consist of only one gene that codes just for the enzyme that transports it (transposase)
2. complex transposons code for extra features: replication, antibiotic resistance

74
Q

pseudogenes

A

the human genome contains many types of DNA that do not actually code for proteins or RNA, and because most of the genome appears to be repetitive DNA, there are lots of transposable elements present as well

pseudogenes are former genes that have accumulated mutations over a long time and no longer produce a function protein

75
Q

how many genes are in the human genome?

A

~24,000
majority consisting of repetitive DNA

76
Q

virus

A
  • nucleic acid - RNA or DNA that can be double or single stranded
  • capsid - a protein coat that encloses the nucleic acid
  • capsomeres - surrounds capsid of some viruses and incorporates phospholipids and proteins obtained from the cell membrane of the host
77
Q

bacteriophage

A

a virus that only attacks bacteria, is usually specific to a type of cell via viral surface proteins binding to specific receptors on the host cell of the species

78
Q

lytic cycle

A

when the virus penetrates the host cell membrane and uses host machinery to produce nucleic acids and viral proteins that are then assembled to make new viruses
a) these viruses then burst out of the cell
and infect other cells

DNA viruses - replicate by first replicating DNA and forming new viral DNA, which is then transcribed to produce viral proteins that combine with DNA to form new viruses

RNA virus - RNA serves as mRNA which is translated into protein. this protein and RNA assemble to form a new RNA virus

retroviruses - single stranded RNA viruses that use reverse transcriptase to make a DNA complement of their RNA by hijacking the host cell’s replicating machinery. this RNA is then used to manufacture mRNA or enter the lysogenic cycle (becoming incorporated into the host DNA)
- a common example of a retrovirus is HIV

79
Q

lysogenic cycle

A

when viral DNA is incorporated into the DNA of the host cell; there are two phases to this cycle:

a) dormant stage - the virus is referred to as a provirus and remains inactive until an external stimuli triggers the virus
b) when triggered, the virus enters the lytic cycle, and follows the same steps as mentioned in the previous bullet

80
Q

steps of the lytic cycle

A
  1. attachment: the phage attaches to the surface of the host
  2. penetration: the viral DNA enters the host cell
  3. biosynthesis: phage DNA replicates and phage proteins are made
  4. maturation: new phage particles are assembled
  5. lysis: the cell lyses, releasing the newly made phages
81
Q

prions

A

are not viruses or cells, but are infectious, mis-folded versions of proteins in the brain that cause normal versions of proteins to also become mis-folded. prions are fatal, and are implicated in diseases such as Mad Cow disease, kuru, scrapie in sheep, and Creutzfeldt-Jakob disease

82
Q

viroids

A

very small circular RNA molecules that infect plants. these do not encode for proteins, but replicate in host plant cells via host enzymes, and cause errors in the regulatory systems of plant growth

83
Q

binary fission

A

bacteria reproduce via this method in which the chromosome replicates, the cell divides into two cells, and each cell now holds the exact same copy of the original chromosome

84
Q

plasmids

A

short, circular DNA outside of chromosomes that carry genes that are beneficial, but not essential for survival

have a restriction site, LacZ gene, and ampicillin resistance gene

85
Q

episomes

A

plasmids that can incorporate bacterial chromosomes

what help bacteria gain characteristics like antibiotic resistance

86
Q

conjugation

A

donor bacteria produces a bridge (pilus) and connect to the recipient bacteria; this allows the donor to send a chromosome or plasmid to the recipient, thus allowing recombination to occur

a. an F plasmid allows a pilus to form, and once the recipient receives the F plasmid, it is now F+ and can donate this plasmid as well
b. pili are also used for cell adhesion

87
Q

transduction

A

DNA is introduced into a genome via virus. when the virus is assembled during the lytic cycle, some bacterial DNA is incorporated in the place of viral DNA. when the virus infects another host, the bacterial DNA part that it delivers can recombine with the resident DNA

88
Q

transformation

A

bacteria take in DNA from surroundings and incorporate it into the genome

89
Q

operon

A

region of DNA that controls gene transcription and consists of
i. promoter: sequence of DNA where RNA polymerase attaches to begin transcription
ii. operator: region that can block action of RNA polymerase if occupied by repressor proteins
iii. structural genes: DNA sequences that code for related proteins
iv. regulatory genes: located outside of operon region, and produce repressor proteins. others produce activator proteins that assist the attachment of RNA polymerase to the promoter region

90
Q

Lac operon (E.coli)

A

controls the breakdown of lactose; the regulatory gene produces an active repressor that binds to the operator and blocks RNA polymerase
i. the lac operon consists of three lac genes (Z,Y,A), which code for the following:
a. B-galactosidase that converts lactose –> glucose and galactose
b. lactose permease that transports lactose into the cell
c. thiogalactoside transacetylase
ii. when lactose is available, lactose binds to the repressor and inactivates it, therefore allowing RNA polymerase to transcribe the genes. Moreover, lactose induces the operon, and the enzymes that the operon produces as a result are termed “inducible enzyme”

91
Q

cAMP

A

when glucose is low, cAMP is high. this cAMP binds to a CAP binding site of the promoter, which enhances the binding and transcription via RNA polymerase, allowing for lactose to be broken down

if lactose AND glucose are high, the operon is shut off
this is because cAMP is low, and doesn’t bind to CAP. bacteria uses one sugar at a time, and prefers glucose

92
Q

Trp operon

A

produces enzymes for tryptophan synthesis; regulatory genes produce and inactive repressor, which allows RNA polymerase to produce enzymes

i. when tryptophan is available, we no longer need to synthesize it internally: it binds to an inactive repressor and activates the repressor, which binds to the operator and blocks polymerase. Tryptophan is a co-repressor here

93
Q

repressible enzymes

A

are when structural genes stop producing enzymes only in the presence of an active repressor. unlike repressive enzymes, some genes are constitutive (constantly expressed) either naturally or due to mutation

94
Q

regulatory proteins

A

repressors and enhancers/activators that influence RNA polymerase attachment to the promoter region.
i. utilizing the presence or absence of activators allows for cell type-specific transcription (for example: a liver versus a lens cell transcribe different genes)

95
Q

nucleosome packing

A

involves regulation at the chromosome level
i. methylation histones - results in tighter packing that prevents transcription
ii. acetylation of histones - uncoils chromatin, encouraging transcription
iii. direct DNA methylation - epigenetic control of DNA that can be inherited and usually leads to lower expression

96
Q

RNA interference

A

noncoding RNA (ncRNA) plays a role in controlling gene expressions as well. some are even involved in chromatin modification
i. micro RNA (miRNA) - single stranded RNA molecules that bind to complementary RNA sequences and either degrade the target or block its translation

97
Q

short interfering RNA (siRNA)

A

function similarly to miRNA, aside from a subtle difference between the precursors
a. in both cases, double stranded RNA becomes single stranded and then carries out its function
b. RNA interference (RNAi) is the blocking of gene expression using siRNAs

98
Q

human genome

A

97% of human DNA does not code for protein product, but rather for non-coding DNA
i. non-coding DNA includes regulatory sequences, introns, tandem repeats, and repetitive sequences that are never transcribed
ii. tandem repeats are abnormally long stretches of back-to-back repetitive sequences within an affected gene (e.g. Huntington’s)

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