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a form of inheritance that is superimposed on the genetic inhertance based on DNA

epigenetics

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No change in actual structure of the gene, no nucleotide change... change in chromatin structure which turns gene off or on... chromatin change acures in germ cells

epigenetics inheritence

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DNA sequnce changes

genetic inheritence

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high degree of conservation in a structure indicates

high degree of importance

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one form of chromatin silences the genes it packages without regard to sequence and is directly inherited by daughter cells

heterochromatin

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heterochromatin

-heavily conserved
-thought to be late replicating and genetically inactive
- highly conserved at centromeres and telomeres
-contains very few genes; resistant to gene expression
-all the rest is less condensed and known as euchromatin

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activity a gene depends on position on chromosome... will be silenced if relocated near heterochromatin

position effect.

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breakage events that bring heterochromatin near active genes tends to silence them

position effect variegation.... zone of inactivation spreads a different distance in different cells

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Histone modification

amino acid side chains of histones are subject to a vairety of covalent modifications
-

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histone modification- loosens chromatin sturcutre

Acetylation of lysines... added by histone acetyl transferases (HATs); removed by histone deacetylase complexes (HDACs)

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Histone modifications of serines

phosphorlation

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What does recruitment of enzymes that cause histone modification depend on?

gene regulatory proteins

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Are histone modifications reversible?

All are reversible, but can persist long after regulatory protieins have disappeared

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What is important consequences for the types of proteins the modified DNA attract?

This determines the how when if gene expression takes place

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What histone hast no variant histones?

H4

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synthesized during S phase and assembled into nucleosomes on duaghter DNA helices just behind replication fork

major histones

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synthesized during interphase and inserted into already formed chromatin. requires histone exchange process catalyzed by chromatin remodeling complex

variant histones

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Histone code

thouseand of combinations of modifications (methylation, acetylation, etc)... ready by code reader complex

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What binds and attracts other components??

code reader complex.. brings onther protein compexes

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gene regulatory proteins has a histone modyfing enzyme " writer", the code-reader protein tells the other DNA about the change

code reader-writer

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IS the chromatin remodeling comlex ATP dependent?

Yes,

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How is remodeling contained to one area of the chromosome?

physical barriers... nuclear 4 complex, code reader complexes cannot go through
enzymatic barriers- HS4 region- protects the Beta globin locus from silencing, contains a cluster of histone actylase binding sites prevening writers from continuing

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centromeric heterochromatin

centromere specific H3 histon, CENP-A, pack the nucleosoomes into dense arrangements to for the kinetochore

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What does centromere sequences in humans consist of?

short repetitive DNA sequences called alpha satellite DNA

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What is centromerica heterochromatin defined by?

assembly of proteins, not DNA sequences

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alpha satellite DNA

at most centromeres, but not all. and at some areas that are not contromeres, the proteins that form to create the centromere is the MOST important aspect of centromere formation

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What are 2 altering types of chromatin

nucelosomes w CENP-A on the outside fold
Nucleosomes w normal H3 on the inside

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What does CENP-A do?

binds the kinetochore

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What does de novo centromere formation require?

a "seeding" event on alpha satellite DNA

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How are H3-H4 tetramers inherited?

Directly inherited by the daughter strands at the replication fork

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Centromeres are not randomly placed on

chromosomes

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structure of interphase chromosomes

extended loops to be more accesible

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What is assocated with nuclear lamina?

heterochromatin

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Each chromsomes occupies

its own areas of the nucleus, not each pair is next to one another

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Chromatin structure and location chagnes during

gene expression

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If a gene is being expressed it goes to?

a chromosomes loop

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decondensation of chromatin during gene transcription;

chromosomes puffs

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interior of nucleus very

hertogeneous

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mitotic chromosomes are

highly condensed, final levle in chromosome packaging

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two daughter DNA molecules replicated in interphase are speartely folded to produce

two sister chromatids

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What are chromatids held together at?

chromatids

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What is the purpose of consensation

protection of fragile DNA molecules
allow for separation for cell division

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Compaction aided by proteins called

condensisns

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genes that are similar in both sequence and fucntion due to common ancestry***

homologues... not the same as syntany

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What is a major clue to gene and prtein function?

recognition of sequnce similarity

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gene sequences are more tightly conserved than...

genome structure.... size of genome, number of genes, size of introns, abundance of repetitive sequences can be quite different

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How do genomic changes occur??

mistakes in DNA replication and repair... rare in genetic material

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types of genetic changes

base pair substitutions...
more lg scale=
duplications, deletions, inversinos, translocations

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elimination of mutations that interfere with improant genetic functions

purifying selection

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a duplicated gene that has become irreversibly inactivated by multiple mutations

pseudogenes

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globin genes... duplication and divergence

intially there was one hemoglobin genes and now it has four.

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SNPs. single-nucleotide

points in the gneome where one group has one nucleotide and another group as another
variation occurs at a high rate (1% or more)

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CNVs- copy number variants

presence of many duplications and deletions of lg blocks of DNA
some blocks are common and others rare