Lectures 10-12 Flashcards
aneuploidy
loss or gain of chromosomes - monosomy or trisomy
euploidy
complete haploid sets of chromosomes are present
polyploidy
more than two sets of chromosomes are present
autopolyploidy is when…
organisms have more than two sets of chromosomes from the same species
allopolyploidy is when…
organisms have more than two sets of chromosomes from different species via hybridization
autopolyploidy is a failure of…
chromosomes to segregate during meiotic division resulting in diploid gamete
allopolyploidy results from…
hybridizing two closely related species; chromosomes are NOT homologous; ex. mules
nondisjunction
chromosomes (HC or SC) fail to separate in meiosis or mitosis
2 examples of nondisjunction disorders
1) Turner Syndrome - X0
2) Klinefelter Syndrome - XXY
3 times when nondisjunction can occur
1) anaphase of mitosis
2) meiosis I - tetrads fail to separate
3) meiosis II - SC fail to separate
nondisjunction is meiosis I results in…
2 n+1 gametes and 2 n-1 gametes
nondisjunction in meiosis II results in…
2 normal gametes and 2 abnormal gametes
what causes nondisjunction?
- spindle-assemble checkpoint
- female meiosis is more error prone
- age-cohesin degrades during meiotic
arrests in oocytes
- age-cohesin degrades during meiotic
monosomy may cause haploinsufficiency which is when a…
single copy of gene is insufficient to provide life-sustaining for organism
trisomy
extra chromosome which produces more viable organism than if there were a loss of a chromosome
deletion
chromosome is missing a region
terminal deletion
deletion occurs near one end of chromosome
intercalary deletion
deletion from interior of chromosome
deletion/compensation loop
synapsis occurs between normal homolog and the chromosome with intercalary deletion; unpaired region on normal homolog buckles out to allow synapsing
chromosomal duplications are repeated segments of a chromosome that arise through 2 ways…
1) through replication error prior to meiosis
2) through unequal crossing over between synapsed chromosomes during meiosis
3 results of duplications
1) gene redundancy - multiple genes that perform the same function
2) phenotypic variation
3) source of genetic variability during evolution
gene redundancy - rRNA
multiple copies of genes code for rRNA and gene product is essential in abundance in a cell to support protein synthesis
how do new genes arise?
1) non-functionalization - loss of function
2) neo-functionalization - gain of new function
3) sub-functionalization - gene has multiple functions
inversion
rearrangement of linear gene sequence - no loss of genetic info
inversions require…
loop formation, two breaks in chromosome, and subsequent reinsertion of inverted segment via ligation
paracentric inversion
does not include centromere
pericentric inversion
includes the centromere
linear (normal) synapse is not possible if…
if only one member of homologous pair has inverted segment
inversion heterozygotes are organisms with…
one inverted chromosome and one non-inverted homolog
pairing between one inverted chromosome ad one non-inverted homolog requires…
inversion loop
crossover within paracentric inversion heterozygotes produces two recombinants…
dicentric chromatid - 2 centromeres
acentric chromatid - no centromeres
translocations
movement of chromosomal segment to new location in genome
reciprocal translocation
exchange of segments between 2 non-homologous chromosomes; genetic info is not lost or gained; does not alter viability of individual
2 possible segregation patterns for translocation heterozygotes
1) alternate segregation
2) adjacent segregation
alternate segregation leads to…
normal and balanced gametes
adjacent segregation leads to…
gametes containing duplications and deficiencies
non-reciprocal translocation
one-way translocations in which a chromosomal segment is transferred to a non-homologous chromosome
