10.2 Flashcards
What is an aneuploidy? What is polyploidy?
- aneuploidy is an increase or decrease in an individual chromosome (eg: trisomy)
- polyploidy is an increase in the number of sets of chromosomes (eg’; triploid = 3 of every)
What are the 4 most common types of aneuploidy?
- monosomy (2n-1), trisomy (2n+2), nullisomy (2n-2), tetrasomy (2n+2)
What are the variations in aneuploidy?
non homologous:
- 2n-2 = double monosomic
- 2n+2 = double trisomic
homologous:
- 2n-2 = nullisomy
- 2n+2 = tetrasomy
what are the origins of aneuploidy? Are both trisomy and monosomy viable?
- non disjunction during meiosis OR a deletion of a centromere (which leads to losing entire chromosome)
- trisomy is normally viable but monosomy is NOT (unless its gametes)
are homologous or non-homologous aneuploidies more common?
- homologous
what are the human chromosome disorders?
- patau syndrome, Edwards syndrome, Down syndrome, turners syndrome, klinefelters syndrome
- note that the frequency increases as the chromosome gets smaller (since a mutation would be more prevalent)
what is primary Down syndrome?
- trisomy 21
- the most common cause of Down syndrome :
- most cases arise from non-disjunction during meiosis
- ~75% cases the extra chromosome is maternal in origin
What is the relationship between age and Down syndrome incidence?
- increasing maternal age leads to increasing rates of Down syndrome
What is familial Down syndrome?
- in this case parents is a translocation carrier: 45 chromosomes, one is translocation chromosome (still has the amount of chromosomes to function properly)
- extra copy of chromosome 21 is added to another (14 or 15) in ~3-4% of cases
- arise in offspring of parent that underwent robertsonian translocation ( exchange of long arms of non homologous afrocentric chromosomes)
Do plants or animals tolerate aneuploidy better?
- plants tolerate it better: reduced fertility of phenotype may be altered
What is polyploidy?
- an increase in the number of sets of chromosomes
- triploid, tetraploid, pentaploid, etc
= common in plants, less common In animals (lethal to mammals)
Why is polyploidy important to plants?
- plays a key role in their evolution
- 30-35% of angiosperms evolved via some form of polyploidy
What are the two types of polyploidy?
- autopolyploidy: multiples of the same genome
- allopolyploid” : multiples of closely related genomes
what are the origins of autopolyploidy?
- nondisjunction during mitosis results in autotetraploid
- nondisjunction during meiosis can result in diploid gametes (2n+n = 3n, or 2n+2n = 4n)
what are the impacts of autopolyploidy?
- usually sterile
- most gametes produced are genetically unbalanced
what is required to convert a sterile hybrid into a fertile new species?
- chromosome doubling
- unbalanced gametes are non-viable
- so doubling them solves fertility problem, everything is paired
what is the significance of polyploids in agriculture?
- cell volume is correlated with nucleus volume, which is associated with genome size
- often polyploids have bigger leaves and fruit and seeds
- bread wheat!
What are some examples of polyploid foods?
- larger fruit: strawberries, grapes
- production of seedless fruit (sterile) ie: 3n bananas are sterile
why are 3n bananas in trouble?
- 1980s a strain of fusarium appeared in Malaysia : Cavendish has no resistance
- breeding market desirable, resistant bananas is hard
