Lecture 9 - Chromosomal Abnormalities Flashcards
What are the three types of chromosome mutations
rearrangements, aneuploids, polyploids
What do chromosome rearrangements do generally
alter the structure of chromosomes
What are the 4 types of chromosome rearrangements
duplications, deletions, inversions, translocations
What is the definition of an aneuploid
they have an altered number of chromosomes in terms of being added or deleted
What is the definition of a polyploid
one or more complete sets of chromosomes are added or deleted
What is the definition of duplications and what are the two types
segment of a chromosome is duplicated
Tandem duplications
Displaced duplications
What is the definition of a tandem duplication
duplicated regions are adjacent to the original section
What is the definition of a displaced duplication
duplicated region is elsewhere in the genome
What is the outcome of homozygous duplications during replication
not a problem during replication
What is the outcome of heterozygous duplications during replication
chromosomes are not the same length, the duplicated chromosome has to form an inversion loop so regions can line up
Define unbalanced gene dosage
if genes are duplicated it can lead to a greater production of those gene products which can affect phenotype
What percentage of human genome contains segmental duplications
4%
Explain the role of duplication in evolution
- existing copies of a gene are not free to vary if encoding something essential
- if that gene gets duplicated extra copies can undergo mutation and change
- over time extra copy might acquire enough mutations to assume new function to organism
Define a deletion
segment of chromosome is deleted
What are the effects of heterozygous chromosomes concerning a deletion during replication
the longer wild type chromosome must form an inversion loop to line up with the chromosome with a deletion
What are the effects of a homozygous deletion
It is lethal in the homozygous due to loss of essential genes
Define haploinsufficient and what type of chromosomal rearrangement is it associated with
Associated with deletions when a single copy of a gene is not sufficient to produce a wile type phenotype
Define inversions and what are the two types
when chromosome segment gets inverted
paracentric inversions
Pericentric inversions
What are paracentric inversions
inversions do not span the centromere
what are pericentric inversions
inversions do span the centromere
What are the effects of inversion on phenotype
typically profound effect
can disrupt gene or gene order
Does a homozygous individual for a particular inversion have problems in meiosis
no problems
Does a heterozygous individual for a particular inversion have problems in meiosis
Yes needs a 4 strand inversion loop
What are the results in the gametes of a heterozygous paracentric person where the chromosomes have crossed over in the inversion loop
1 non-recombinant gamete with no inversion
2 recombinant short nonviable gametes
1 non-recombinant gamete with paracentric inversion
What are the results in the gametes of a heterozygous pericentric person where the chromosomes have crossed over in the inversion loop
1 non recombinant gamete with no inversion
2 recombinant long nonviable gametes
1 non recombinant gamete with pericentric inversion
What is distinguishable between paracentric and pericentric inversions during crossing over in meiosis
Paracentric inversion leads to formation of a dicentric chromatid and an acentric chromatid
What is the definition of a dicentric chromatid
has two centromeres
What is the definition of an acentric chromatid
lacks a centromere
What is the definition of a translocation
movement of genetic material between non homologous chromosomes or within the same chromosome
What are the effects of translocations
link genes that were originally located on different chromosomes
can disrupt gene sequences
Define robertsonian translocation and what is the overall result on the genome
deletion associated with translation where two long arms are joined together and two short arms are joined and lost
Overall result is a reduction in chromosome number by 1
Can aneuploidy happen in meiosis or mitosis
both
can aneuploidy happen in meiosis I or II
both
What are the 3 specific ways that aneuploidy can happen
- centromere gets deleted
- small chromosome lost in robertsonian translocation
- nondisjunction and failure of homologous chromosomes or sister chromatids to separate
What are the 4 types of aneuploidy and what is the math that goes with them
nullisomy 2n-2
Monosomy 2n-1
trisomy 2n+1
tetrasomy 2n+2
What are the rates of aneuploidy in human pregnancy
30% of conceptions aborted and 50 % of those due to aneuploidy
What causes trisomy 21
nondisjunction in oogenisis
Primary down syndrome is what
not heritable resulting from spontaneous nondisjunction in oogenisis
What is maternal age linked to increased rates of down syndrome
oocytes suspended in diplotene for a long period of time start to have cohesin in spindle structure break down leading to nondisjunction of chromosomes.
What is the definition of familial down syndrome
Parents who are carriers of chromosomes which have undergone robertsonian translocation
Long arm of 21 and 14 join together
Gametes can segregate 6 different ways, 3 of which will cause a live birth , 1 of those ways leads to down syndrome`
What are the two types of polyploidy
autopolyploidy and allopolyploidy
Define autopolyploidy
ploidy event that derives from a single species caused by accidents in mitosis or meiosis
Define allopolyploidy
arises from hybridization between two species where one species carries chromosome sets from two or more species
What ploidy are allopolyploidy hybrids
diploid
Cell volume is correlated to what
nuclear volume
