10.1 Flashcards
what are the two types of chromosome variations?
chromosome rearrangement
changes in chromosome number
what are chromosome variations?
permanent chromosomal changes that can be passed down to offspring (if they are in germline cells)
what are the four types of chromosome rearrangements?
deletions
duplications
inversions
translocations
what is chromosome deletion?
loss of a segment of chromosome
how do chromosome deletions happen?
terminal ends breaking off or internal breaking and rejoining at incorrect ends
what is the main effect of chromosome deletions?
loss of genetic information
how are chromosome deletions detected?
when the chromosomes pair in prophase I, the longer one bunches up to match the shorter one, forming a deletion loop that can be detected during meiosis
OR by molecular methods that detect heterozygosity or gene dosage
what happens if a chromosome deletions happens spanning the centromere?
forms an acentric chromosome that will most likely be lost in cell division and may be lethal
what is pseudodominance?
expression of alleles that are normally recessive
what are the possible consequences of chromosome deletions?
change in gene dosage
pseudo-dominance
acentric chromosomes
haploinsufficiency
how does chromosome deletions cause pseudodominance?
it deletes the part of the chromosome with the dominant allele
what is haploinsufficiency?
mutant phenotype because gene dosage is too low (requires two copies for normal protein production)
what is Cri du chat?
a genetic disorder related to gene dosage and chromosome deletions
what is chromosome duplication?
repetition of a chromosome segment
what are the simplest form of chromosome duplication?
tandem duplication
what affect do chromosome duplications have?
usually not much, but gene dosage changes can cause problems, help evolution
what effect do chromosome duplications have on evolution?
provide extra genetic material for new genes and adaptations
what are the origins of chromosome duplications?
unequal crossing over of misaligned chromosomes during meiosis (also creates deletions)
how are chromosome duplications detected?
when the chromosomes pair in prophase I, the longer one bunches up to match the shorter one, forming a deletion loop that can be detected during meiosis
OR by molecular methods that detect gene dosage
what are the evolutionary consequences of chromosome duplications?
both copies may remain the same, alters gene dosage
one coy may become inactive and form a pseudogene and accumulate lots of mutations
one copy may aquire a new function (neofunctionalization)
what are the long-term effects of neofunctionalization?
creates new genes and multigene families
what effect does gene dosage have?
may affect phenotype
amount of protein created is often proportionate
what is an example of gene dosage affecting phenotype?
drosophila eyes (Bar mutant)
what are chromosomal inversions?
two breaks on a chromosomes and reinsertion in the opposite orientation
what are the types of chromosomal inversions?
pericentric (around centromere)
paracentric (beside centromere)
what is the effect of chromosomal inversions on phenotype?
often nothing
sometimes change in position may later expression (genes near chromatic may not be expressed)
what happens with chromosomal inversions during crossing over?
if crossing over doesn’t occur - viable
if crossing over occurs OUTSIDE inverted region - viable
if crossing over occurs INSIDE inverted region - some nonviable and reduced recomb frequency
why is crossing over in the chromosomal inversion region non-viable?
chromosomes form a dicentric chromatid with a bridge that breaks and gets rid of the acentric chromatid and gets rid of the genes :(
what does inversion result in (summarized)?
functional suppression of recombinance and potential loss of fertility
what is chromosome translocation?
exchange of segments between non-homologous chromosomes (or to different region on same chromosome
what are the two types of chromosome translocation?
reciprocal and non-reciprocal
what is a balanced translocation?
a chromosome translocation where no genetic material is lost
what are the consequences of chromosome translocation?
may alter expression of genes because of associations or form new gene products
what is the philadelphia chromosome?
fused BCR-ABL gene
produces fusion protein that causes chronic muelogenous leukemia
