Chapter 17(3) Flashcards
What is down syndrome caused by?
chromosomal aberration
What are the 4 Euploids and their designated ploidy level?
-monoploid: n
-diploid: 2n
-triploid: 3n
-tetraploid: 4n
What are the four Aneuploids and their designated ploidy level?
-monosomic(missing one copy of one chromosome): 2n-1
-trisomic(an additional copy of one chromosome): 2n+1
-nullisomic(no copies of a particular chromosome): 2n-2
-disomic(in haploid organisms, when one chromosome is present twice): n+1
What is Euploidy?
sets of haploid chromosome numbers
Why does meiosis work in eukoryotes with an even number of chromosomes (2n, 4n, 6n, etc.)?
because of the need to pair with homologs
-Meiosis in 3n, 5n, 7n, etc. will fail
because some chromosomes will not pair with a homolog.
What happens in autoploidy?
- fertilization by multiple pollen grains
- increase in chromosome number by mitotic nondisjunction
- increase in chromosome number by meiotic nondisjunction
What happens in allopolyploidy?
duplication of euploid chromosome sets from a combination from different species
Does allopolyploidy result in fertile offspring?
-interspecific hybrid is infertile due to nonhomology of chromosomes
-after genome duplication, homologous chromosome pairing and disjunction, the interspecies hybrid is fertile and can reproduce
What is Aneuploidy?
when the number of chromosomes in a cell differs from the wild type by a portion of a haploid set
-most often deleterious and can result in the early death of embryos during development
What is non disjunction?
origin of aneuploidy; failure of segregation of chromosomes during meiosis or mitosis
Where does non disjunction commonly occur and why?
more can go wrong during meiosis 1 because of the additional steps, such as the formation and maintenance of tetrads
Do males or females introduce more aneuploidies? Why?
females because of the arrest of meiosis in primary oocytes
Why is aneuploidy detrimental?
gene imbalance–>transcript imbalance–>protein imbalance
What needs to occur for chromosome rearrangements to occur?
we need a double-stranded DNA break AND repair (otherwise, the break can be lethal for a cell)
What is it and what occurs during unequal crossing over?
-Recombination usually involves the equal exchange of genetic material between homologous chromosomes, but sometimes there can be an unequal transfer.
-While rare, this usually occur when genes have been duplicated and the
recombination machinery gets confused.
What is a microdeletion?
a chromosomal aberration where the deletion is small enough to be undetected in a microscope via banding (unlike big deletions)
What is an inversion?
when a chromosomal break (double-stranded DNA breaks) can reattach, but this happened in the reverse orientation
What is a translocation?
A chromosomal break (double-stranded DNA breaks) that reattaches, but on different chromosomes
Do inversions and translocations have any phenotypic consequences?
As long as genes or regulatory
regions are away from the
breakpoints, the inversions and
translocations will likely not have
phenotypic consequences except
for reduced fertility due to problems at meiosis
What is a meiotic consequence of inversions?
inversions loops can result in major chromosomal deletions after recombination in an inversion heterozygote
What are translocations?
chromosomal breakage followed by reattachment of the broken segment to a nonhomologous chromosome
How is fertility impacted by the size of an inversion?
-The larger the inversion, the more likely the individual will exhibit lower fertility because of the production of inviable gametes
-Smaller inversions are likely to
still produce viable gametes because crossovers will occur outside of the inversion.
What are two types of translocations?
- unbalanced translocation
- reciprocal balanced translocation
What are the 3 types of reciprocal balanced translocation and which produces viable offspring?
- Alternate segregation(about 50%): separates homologous centromeres and produces normal gametes
- Adjacent-1 segregation(about 50%): separates homologous centromeres and produces nonviable gametes with duplications and deletions
- Adjacent-2 segregation(very rare): vare rare because it does not separate homologous centromeres; gametes are nonviable due to duplications and deletions
-only alternate segregation produces viable gametes and progeny; this segregation pattern occurs in about half of meioses and accounts for semisterility of translocation heterozygotes
