Genetics Unit 11

chromosomal mutations

mutations in a chromosome regions that encompasses multiple genes

aneuploidy

chromosome abnormality characterized by the gain or loss of one of a few invidual chromosomes; not an exact multiple of the haploid set

polyploidy

a condition where the cell contains 3 or more complete sets of haploid chromosomes

nondisjunction

failure of homologous chromosomes or sister chromatids to separate correctly during cell division

trisomy

gain of one chromosome (2n+1)

monosomy

loss of one chromosome (2n -1)

tetrasomy

gain of a pair of chromosomes (2n+2)

nullisomy

loss of a pair of chromosomes

autopolyploidy

occurs when extra chromosome sets originate from the same species; can occur through failure of meiosis or failure in mitosis

triploidy

3 complete sets of chromosomes; sterile in plants and lethal in animals; can be due to fertilization of an egg by 2 sperm

tetraploidy

four complete sets of chromosomes; advantageous in plants

unbalanced chromosomal arrangements

change in amount of total genetic material through deletion or duplication

balanced chromosomal arrangements

rearrangement of existing material through inversions or translocation

gene balance

fundmental principle that explains why changes in dosage of individual genes or chromosomes; cellular machinery relies on stoichiometric balance among proteins produced by interacting genes

gene mutations

mutation that occurs within a single gene

nondisjunction

primary cause of mutation causing abnormal number of chromosomes

gametes

nondisjunction during formation produces extra chromosome or missing chromosome

somatic cells

nondisjunction after fertilization leads to mosaicism

mosaicism

some cells in the body have a normal chromosome count and some are aneuploid

monosomics

missing one copy of a chromosome

autosomes

monosomics for any generally die in utero

x chromosome

monosomics cause death in utero

turner syndrome

genetic condition that effects individuals who are biologically female; absence of all or part of one X chromosome; 45 total chromosomes

trisomics

contains an extra copy of one chromosome; can result in abnormalities or death

Klinfelter syndrome

a commone sex chromosome aneuploidy that affects males; presence of an extra X chromosome; 47 chromosomes XXY

down syndrome

trisomy 21; most commone aneuploidy in humans; caused by presence of extra full or partial copy of chromosome 21; 47 chromosomes

trisomy 21, translocation, and mosaic

3 causes of down syndrome

advanced maternal age

higher incidence of down syndrome is related to

polyploidy

cell contains 3 or more complete sets of haploid chromosomes; lethal in animals and common in plants

allopolyploidy

form of polyploidy where an organism processes multiple complete sets of chromosomes derived from different species; resulting hybrid is often sterile

unbalanced rearrangements

change in the total amount of genetic material; deletion or duplication

deletion

loss of chromosome segement

duplication

copy of chromosome segment

balance rearrangement

rearrangement of existing material; inversion or translocation

inversion

segments within a chromosome can be reversed

translocation

movement of a segment to a different chromosome

terminal deletion

loss of segment near the end of a chromosome; fragment containing telomere is lost

interstitial deletion

loss of segment internally on the chromosome

happloinsufficiency

deleted region may contain a gene where having only one functional copy is not enough for normal function

pseudodominance

deleted segment included the dominant allele of a gene, the remaining recessive allele will be expressed

severity

depends on size of the deletion and the specific genes located within the deleted segment

cri-du-chat syndrome

caused by deletion of genetic material from the end of the short arm of chromosome 5; 44 total chromosomes

de novo

spontaneous cause of cri-du-chat syndrome; paternally originated

inherited translocation

deletion is inherited from a parent who carries a balanced chromosomal translocation involving chromosome 5

tandem duplication

located immediately adjacent to the original segment

reverse tandem duplication

segment is flipped but still adjacent to the original segment

displaced duplication

located in a different location on the same or different chromosome

gene dosage imbalance

extra copy of genes disrupts normal stoichiometry of gene products

paracentric inversion

inverted segment does not incude the centromere

pericentric inversion

inverted segment includes the centromere

inversion loop

allows homologous genes to pair during meiosis I

paracentric inversion crossing over

produces an acentric fragment and a dicentric chromosome; highly unstable

pericentric inversion crossing over

produces chromosomes with both a duplication of one segment and deletion of another

reciporcal translocation

exchange of segments between two non-homologuous chromosomes

robertsonian translocation

occurs between two acrocentric chromosomes

inverse dosage effect

cell usese to cope with imbalance; partial attempt to re-establish a stable genomic balance

proto-oncogenes

normally activates cell division; can cause cancer if always on

oncogenes

mutated version of proto-oncogenes

tumor supressor genes

inhibit cell division; if off can cause cancer

chimeric proteins

entirely new, often active function; becomes oncogenic

forced dimerization

fusion causes new protein to dimerize, which mimics growth signal factor; drive proliferation