Topic 19: Chr Rearrangements, Aneuploidy, Polyploidy

chromosomal rearrangement

any structural change of a chromosome

chromosomal deletion

a segment of the chromosome is gone

chromosomal duplication

a segment of the chromosome is duplicated

chromosomal inversion

segment of the chromosome is reversed

translocation

exchange of arms between heterologous chromosomes

reciprocal translocation

two way exchange where chromosomes swap segments

can result in reduced fertility

nonreciprocal translocation

one way exchange where a chromosome breaks and attaches to another with no exchange back

can result in three copies of genes in the affected area

chromosome break

disruption in the physical structure of a chromosome

nonhomologous end joining

broken ends of different DNA molecules are ligated together

gene dosage imbalance

there are fewer or more than normal copies of a gene, this may impalace the level with other gene products and cause an abnormal phenotype

haploinsufficiency

abnormal phenotype comes from lack of gene product

gene fusion

two genes fuse together, usually nonfunctional. occasionally a new fusion gene is introduced

gene disruption

break or recombination point could fall inside a gene and break it

phenotype is usually loss of function

reduced fertility

phenotypically normal, bu unable to produce viable gametes or embryos

position effect

if a gene changes chromatin environment (ie euchromatin → heterochromatin) the gene may not be expressed even if the sequence is unchanged

gene family

have similar sequence and function but have specialized roles

aneuploidy

missing part of one or more sets

monosomy

having just one member of a pair while the rest are normal

trisomy

having three copies of a pair while the rest are normal

nondisjunction

failure of chromosomes/chromatids to seperate during meiosis

first division nondisjunction

homologs fail to segregate in meiosis I

second division nondisjunction

sister chromatids fail to separate in meiosis II

polyploidy

organism with 2+ complete sets of chromosomes

autopolyploidy

having sets of chromosomes from the same species

allopolyploidy

having sets of chromosomes are from different species

amphidiploid

when an interspecies hybrid undergoes chromosomes doubling, so that it is capable of sexual reproduction

triploid

having 3 sets of chromosomes

tetraploid

having 4 sets of chromosomes

interspecies hybrid

result of mating between two species, usually infertile

chromosome doubling in interspecies hybrid

now there is a partner for chromosomes to pair and sexual reproduction is possible

paleopolyploid

current diploid organisms that have undergone cycles of polyploidization followed by evolution back to diploid