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Flashcards in Chromosomes Deck (75)
1

homologous recombination

DNA segments that are similar to each other break and rejoin to form a new combination

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site specific recombination

nonhomologous DNA segments are recombined at specific sites

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transposable elements

small segments of DNA that move themselves to multiple locations within chromosomal DNA

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harlequin chromosome

reveals recombination after BrdU staining between sister chromatids

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holliday junction

the mechanism of crossing over between two homologous chromosomes

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viral integration

some virus integrate DNA into host chromsome by site specific recombination

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antibody recombination

site specific recombination of v and j regions for light chain; v, d, and j regions for heavy chain variable

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recombination signal

recognition site for site specific recombination between the v and j regions

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NHEJ proteins

non-homologous end-joining proteins; connection phase of V(D)J recombination

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homologous chromosomes

homologs - the maternal and paternal chromosomes of a pair

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human karyotype

cytogeneticists use the 46 human chromosomes displayed at mitosis to view abnormalities

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human genes

approximately 25,000

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Avg gene size

27,000 nucleotide pairs or 9,000 amino acids

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Avg # exons/gene

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nuclease

breaks down DNA by cutting between the nucleosomes

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histone octamer

two molecules each of H2A, H2B, H3, and H4

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Histone

high salt dissociates the ionic (salt) linkages between DNA and histones

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histone deacetylase complex

HDAC-removes acetyl groups (COCH3) from lysine and removing gene expression proteins

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histone acetyl transferase

HAT-commonly adds acetyl group to lysine on histones and recruits proteins that turn on gene expression. Also adds acetyl to transcription factors

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histone methyl transferase

adds methyl groups

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acetylation vs methylation

A methylated lysine cannot be acetylated and vice versa

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histone covalent modifications

acetylation+methylation of lysines, phosphorylation of serine+threonine, methylation of arginine, ubiquityl+sumoyl+biotin of lysine

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Histone synthesis

synthesized during S phase

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histone variants

synthesized during interphase binding to specific chromatin sites

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histone code potential

signals that stretch of chromatin is newly replicated, chromatin damaged or needs repair

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reader-writer complex

A gene regulatory protein will recruit a histone modifying enzyme, which attracts a code reader protein causing a repetitive effect

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barrier sequence

cluster of proteins such as histone acetylase enzymes blocks chromatin condensing

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lampbrush chromosomes

extended meiotically paired chromosomes in amphibian oocytes allows viewing of interphase chromosomes

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polytene chromosome

all homologous chromosomes are side by side and allow viewing of dark heterochromatin DNA bands; first seen drosophila

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Chromosome puff

duirng transcription, the DNA puffs out on a polytene chromosome

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Heterochromatin types

different types of heterochromatin allow different levels of compaction

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nucleus subcompartments

cajal bodies, nucleolus, and repair factories create specialized environments in nucleus

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homologous gene

genes similar in nucleotide sequence and function because of common ancestry

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pseudogene

one copy of a duplicated gene can be seen to have become irreversibly inactivated by multiple mutations

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Globin gene duplications

The globin gene family has duplicated and diverged over eveolution from a single globin to variety of globins during development

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point mutation

change in a single base pair within the DNA

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base substitution

one base is substituted for another base

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transition mutation

base substitution where a pyrimidine is substituted for a pyrimidine or purine for a purine

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transversion mutation

base substitution where a pyrimidine is substituted for a purine

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silent mutation

base mutation that does not alter the amino acid sequence even though the nucleotide has changed

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missense mutation

base substitution where amino acid sequence changes from one amino acid to another with one nucleotide change

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nonsense mutation

change from a normal codon to a stop codon

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operon polarity

nonsense mutation occurs in a bacterial operon it might inhibit downstream gene expression

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frameshift mutation

addition or deletion of a number of nucleotides not divisible by 3

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neutral mutation

silent mutation and when a missense mutation has not detectable effect on protein

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wild type genotype

relatively prevalent genotype and if multiple alleles could have mutliple wild type alleles

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mutant allele

a rare mutation that changes the wild type genotype by altering DNA gene sequence

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conditional mutants

affect the phenotype under a defined set of conditions such as temperature sensitivity

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suppressor mutations

a second mutation that affect the phenotype expression of the first mutation by affecting protein

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intragenic suppressor

when the second mutation is within the same gene (such as LacY) as the first mutation

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intergenic suppressor

suppressor mutation the is in a different gene from first mutation

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promoter mutations

up promoter or down promoter mutations affect transcription

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splice mutation

mutations in eukaryotic genes can alter splice junctions and affect the order and/or number of exons that are contained within mRNA

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trinucleotide repeat expansion

repeated sequence of 3 nucleotides can readily increase in number from one generation to the next

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position effect mutation

Genes may be moved next to regulatory sequences such as promoters or heterochromatin regions

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genetic mosaic mutation

somatic regions that are genotypically different from each other

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spontaneous mutation

changes in DNA structure that result from abnormalities in biological processes

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induced mutation

abnormalities caused by environmental agents

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spontaneous mutation cause

molecular change in DNA caused by depurination, deamination, tautomeric shift

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depurination

removal of a purine (adenine, guanine) from DNA which breaks covalent bond between deoxyribose and purine causing apurinic site

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deamination

removal of an amino group from cytosine which produces uracil or changes 5-methylcytosine to thymine

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T+G tautomers

common form is keto form and rare is enol form

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A+C tautomers

common form is amino form and rare is imino form

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tautomeric shift

if the base tautomers shift right before DNA replication a mutation can occur

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deamination mutagen

nitrous acid replaces amino groups with keto groups in bases

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hypoxanthine

deamination of adenine. hypoxanthine pairs with cytosine

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5-bromouracil

base analogue that has tautomeric shifts commonly

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UV mutagen

thymine dimers between bases in DNA

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photolyase

in plants and yeast thymine dimers are split

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alkyltransferase

protein removes methyl or ethyl groups from guanine bases mutated by alkylating agents

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base excision repair

enzyme DNA glycosylase that recognizes abnormal bases and cleaves the bond to sugar

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nucleotide excision repair

direct repair of nucleotides

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homologous recombination repair

repairs double stranded breaks by exchanging DNA between broken and unbroken sister chromatids during S and G2 phase

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nonhomologous end joining

repairs double stranded breaks by filling DNA gaps and ligates them together

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bacteria origin of replication

bacterial chromosomes have a single origin of replication and proceeds bidirectionally