chapter 10 part 2

Question 1

changes to chromosome structure can be caused by _____________ _________ or other events

Answer 1

chromosome breakage

Question 2

what can chromosome structure mutations lead to

Answer 2

loss of gain of chromosome segments or partial deletion duplication

Question 3

when a chromosome breaks, where are both DNA strands severed at?

Answer 3

a location called the chromosome break point

Question 4

what can the broken ends do at the chromosome break point?

Answer 4

adhere to each other, to other broken ends, or the termini of other intact chromosomes

Question 5

what can detachment of all or part of one chromosome arm lead to

Answer 5

a terminal deletion
-the broken fragment contains a telomere & some genetic material

Question 6

what may be lost in terminal chromosome deletion

Answer 6

acentric since it lacks a centromere and the spindle fibers cant attach to it

Question 7

what are organisms with one normal & one terminally deleted chromosome called?

Answer 7

partial deletion heterozygotes

Question 8

cru-du-chat syndrome is caused by what

Answer 8

loss of 5p15.2-5p15.3
partial deletion heterozygotes

Question 9

what is an intersitial deletion

Answer 9

the loss of an internal portion of a chromosome, & results from two chromosome breaks

Question 10

are interstitial deletions observed in humans

Answer 10

yes

Question 11

example of interstitial deletions

Answer 11

WAGR syndrome
-series of conditions caused by deletion of multiple genes on chromosome

Question 12

what can unequal crossover result in

Answer 12

partial duplication on one homolog & partial deletion on the other

Question 13

what does unequal crossover take place between

Answer 13

2 homologs

Question 14

partial duplication heterozygote

Answer 14

organism with one normal & on duplicated homolog

Question 15

partial deletion heterozygore

Answer 15

organism with one deleted & one normal heterozygote

Question 16

is unequal crossover common?

Answer 16

no, it does not occur often

Question 17

how does unequal crossover most commonly occur?

Answer 17

when repetitive regions of homologs misalign

Question 18

ex of unequal crossover

Answer 18

williams-beuren syndrome
partial deletion heterozygotes on chromosome 7

Question 19

what can show regions of chromosome duplication or deletion

Answer 19

microscopic observation during prophase 1 when homologs synapse

Question 20

what creates an unpaired loop & what is it?

Answer 20

-when a large deletion or duplication creates an area of mismatch between the altered chromosome & its normal homolog
-the part of one homolog missing on the pairing partner

Question 21

what can large deletion/duplications be detected by?

Answer 21

microscopy that reveals altered chromosome banding patterns

Question 22

what can micro-deletions/duplications be detected by?

Answer 22

FISH
-used to detect the presence or absence of a particular DNA sequence

Question 23

chromosome inversion

Answer 23

reattachment in the wrong orientation

Question 24

chromosome translocation

Answer 24

reattachment to a nonhomologous chromosome

Question 25

paracentric inversion

Answer 25

the centromere is outside of the inverted region

Question 26

pericentric inversion

Answer 26

the centromere is within the inverted region

Question 27

inversion heterozygotes

Answer 27

have one normal & one inverted homolog

Question 28

what can crossing over within a paracentric inversion result in?

Answer 28

-dicentric chromosomes (2 centromeres) -acentric fragment (no centromere) -dicentric chromosome is pulled toward both poles of cell & breaks -acentric fragment is lost

Question 29

what can crossing over within a paricentric inversion result in?

Answer 29

both duplicated & deleted regions in both of the recombinant products

Question 30

what do both pericentric & paracentric inversion recombination result in?

Answer 30

two normal gametes & 2 abnormal gametes

Question 31

what are the three types of translocations

Answer 31

-nonreciprocal translocations -reciprocal balanced translocations -robertsonian translocations

Question 32

nonreciprocal translocations

Answer 32

(unbalanced) arise when a piece of one chromosome is translocated to a non-homolog and there is no reciprocal event -one-way transfer

Question 33

reciprocal balanced translocations

Answer 33

-occur when pieces of two non-homologs switch places -two-way transfers

Question 34

robertsonian translocations

Answer 34

-(chromosome fusions) involve fusion of two non-homologs -reduction in total chromosome number

Question 35

in heterozygotes for reciprocal balances translocations, what occurs?

Answer 35

non of the four chromosomes has a fully homologous partner so an unusual cross-like structure is formed at metaphase 1 of meiosis

Question 36

are translocation heterozygotes sterile? why?

Answer 36

they are partially sterile, only alternate segregation leads to normal gametes (& even the only 1/2 are normal)

Question 37

if two pairs of chromosomes fuse by robertsonian translocation, what happens)

Answer 37

the number of chromosomes drops to 2n-2

Question 38

what is responsible for familial down syndrome

Answer 38

one type of robertsonian translocation between chromosome 21 & (usually) chromosome 14

Question 39

what is DNA & associated proteins of a chromosome called?

Answer 39

chromatin

Question 40

what is chromatin made of

Answer 40

1/2 dna & 1/2 protein (1/2 of protein is made of histone proteins)

Question 41

what are histone proteins

Answer 41

small basic proteins that tightly bind DNA

Question 42

what are the remaining proteins in chromatin

Answer 42

non-histone proteins -very diverse & preform a variety of functions

Question 43

what are the five major histone proteins

Answer 43

H1, H2a, H2b, H3, & H4

Question 44

what are nucleosome core particles?

Answer 44

fundamental units of histone protein organization with two molecules of each of the histones except H1 -forms an octamer

Question 45

core DNA

Answer 45

a span of DNA about 146 bp long that wraps around each nucleosome

Question 46

nucleosome assembly

Answer 46

-H2A & H2B - dimers -H3 & H4 - dimers -H3-H4 dimers form a tetramer -H2A-H2B dimer associate with the H3-H4 tetramer & form an octamer

Question 47

first level of DNA condensation

Answer 47

the wrapping of DNA around the nucleosome -compacts the DNA about 7x

Question 48

linker DNA

Answer 48

the variable-length "string" between nucleosomes -10 nm-fiber

Question 49

is the 10-nm fiber observed under normal cellular conditions?

Answer 49

no. a 30-nm fiber (6 times more condensed) is

Question 50

when does the 30-nm fiber form

Answer 50

when the 10-nm fiber supercoils into a solenoid structure -6-8 nucleosomes/turn & histone H1 stabilizing the solenoid

Question 51

second level of DNA condensation

Answer 51

30nm/solenoid

Question 52

when does chromatin become maximally condensed

Answer 52

in metaphase of mitosis -interphase chromosomes have variably sized loops of 30-nm fibers that form a 300-nm fiber

Question 53

what does chromosome shape depend on?

Answer 53

the chromosome scaffold composed of non-histone proteins

Question 54

what are chromatin loops of 20 to 100 kb anchored to the chromosome scaffold by? at sites called what?

Answer 54

by nonhistone proteins at sites called MARs (matrix attachment regions) -metaphase chromatin is compacted 250-fold compared to the 300-nm fiber

Question 55

what does chromosome compaction allow for?

Answer 55

efficient separation of chromosomes at anaphase

Question 56

what do the chromatin loops formed during condensation play a role in?

Answer 56

regulation of gene expression

Question 57

where does active transcription tale place in?

Answer 57

segments of loops away from MARs

Question 58

what must happen as the replication fork passes

Answer 58

nucleosomes must break down into component parts & release the DNA

Question 59

what happens after replication

Answer 59

the nucleosomes are reassembled, but we need 2X as many now

Question 60

Nucleosomes present after replication typically contain:

Answer 60

-some old histone proteins (epigientic marks) -some new histone proteins -H3 & J4 tetrameres reassociate randomly with one of the sister chromatids -H2A & H2B dimers disassemble & are reassembled from both old & new histones