Ch 8 Chromosome Rearrangments

a piece of the chromosomes may be duplicate, deleted, or inverted

chromosome rearrangements

a segment is misisng, can reduce gene dosage. may expose a recessive allel on the homolog

deletion

a segment is repeated; changes gene dosage, can alter expression and provide material for evolution

duplication

a segment is reversed in orientation (switched around). usually balanced is no DNA is lost/gained, but breakpoints can disrupt genes; crossing ove inside an inversion can produce unbalanced products

inversion

two way exchange of segments between chromosomes

reciprocal translocation

genetic material moves from one chromosome to another without any reciprocal exchang

nonreciprocal translocation

variations in chromosome number and/or structure do periodicallt arise

chromosome mutation

s__m___centric; almsot middle of chromosome- formation postion of telomere

submetacentric

middle of chromosome- formation postion of telomere

metacentric

like the middle of chromosome, but only that half, like a litlle hump - formation postion of telomere

telocentric

a___centric looks like metacentric but the top is two little puffs

acrocentric

deletions lower copy number; duplications raise to it (too much or little gene product can alter phenotype) - effect of rearrangments

gene dosage

a gene moved near different regulatory DNA or into different chromatin may be expressed differently - effect of rearrangements

one part m ay move to a new location, destroying the function of that gene

position effect

Homologous regions must pair; inversions can form inversion loops; crossovers within them may generate abnormal chromatids.; translocations can form multivalent structures; segragation may yield balanced or unbalanced gametes - effects of rearrangments

meiosis

no net loss/gain of DNA (not always harmless)

balanced

DNA is gained/lost

unbalanced

double stranded breaks in DNA cause _____?

cell death

______ duplication- dulicated segment immediately adjacent to original segmen

tandem

_____________duplication- duplicated segment us some distance from the original (on same or different chromosome)

displaced

_______ duplication - duplicated region is inverted (backwards)

reverse

__________ duplications- duplications greater than a thousand base pairs

segmental

the expression of a recessive genetic trait that mimics a dominant inheritance pattern - effects of deletions

pseudodominance

when a single copy of a gene is not sufficient to produce wild-type phenotype - effects of deletions

haploinsufficient

__________ inversion- does include the centromere

pericentric

__________ inversion- does not include the centromere

paracentric

can physically link genes that were formally located on different chromosomes

• new linkage may affect gene expression

• the chromosomes break that brings about _______ may take place within a gene and disrupt it’s function

translocations

____________ translocation- long arms of two acrocentric chromosomes become joined to a common centromere through a translocation

robertsonian

sites that develop constrictions or gaps when the cells are grown in culture and are prone to breakage under certain conditions

fragile sites

present in all humans and are normal features of chromosomes

common sites

found in few people and exhibit Mendelian Inheritance

rare sites

the number of copies of a particular gene varies from person to person

copy number variations

chromosome rearrangements and copy number variants

structural variants

one or more individul chromosomes are added or deleted

• cause 1: deletion of centromere during mitosis and meiosis

• cause 2: Robertsonian Translocation

• non-disjunction

aneuploidy

loss of a single chromosome 2n-1

monosomy

gain of a single chromosome 2n+1

trisonomy

gain of two homologus chromosomes 2n+ 2

tetrasomy

loss of both memebers of a homologous pair of chromosoems 2n - 2

• ie: humans have 2n = 46, _________zygotes has 44

nullisomy

effects of _________

sex chrom ie: turner syn- XO, Klinefelter syn- XXY

Auto chrom ie: trisomy 21- down syndrome

• primary down syn- 75% random nondisjunction in egg formation

• familial down syn- robertsonian translocation between chromosomes 14 and 21

anueploidy

regions of the tissue with different chromosome constituents

• nondisjuction in a miotic division may generate patches of cells in which every cell has a chromosomal abnormality and other patches in which every cell has a normal karyotype

genetic mosaicism

more than 2 sets of chromosomes (3n, 4n)

polyploidy

a genetic condition where an organism has three or more complete sets of chromosome, all originiating from a single species

autopolyploidy

an organism has more than 2 sets of chromosomes combined from two or more different species (hybridization btwn 2 species)

allopolyploidy

______________ significance:

• increase in cell size

• larger plant attributes

• evolution: may give rise to new species

polyploidy