Polidy (Lucy) Flashcards
(56 cards)
What is ploidy?
The chromosome number within a cell or within the cells of an organism
What is euploidy?
Variation in the no. complete sets of chromosome
What is aneuploidy?
Variation in the no. particular chromosomes within a set
Do all cells of an organism always have same amt of DNA?
No, different varieties of a single species may cont different bumbers of copies of the same genome
Why do changes is ploidy matter?
- Change in no chromosome sets in the germ line can give rise to a new variety or species
- May also occur somatically by chance & be pathological/be programmed & be part of developmental program of an organism
- Give rise to –> endopolyploidy & polytenization
- Entire chromosme may also be ‘eliminated’ during development
- Specific seq may be removed; called ‘chromosome dimunition’
Give an example of why polyploidy matters:
Many agriculturally important plants are polyploidy
Strawberries = octoploid strawberries are sold lots in supermarkets over diploid which are smaller
Give an example of polyploidy in amphibians:
African clawed toad = Xenopus laevis (4N) is larger & Xenopus tropicalis (2N)
How is the no. chromosomes represented in a basic ancestral set?
Represented as x - this is the monoploid number
n, the haploid number is no. chromosomes in gamete
What are the names for the number of chromosome sets in somatic cells of the following;
2x =
3x =
4x =
6x =
2x = diploid
3x = triploid
4x = tetraploid
6x = hexaploid
What are the 2 ways polyploids can form?
- Autopolyploids
- Allopolyploids
What are autopolyploids?
All chromosomes from same species; 4x = AAAA
By spontaneous premiotic endoreduplication
What are allopolyploids?
Chromosome sets from different species; 4x = AA BB
By interspecific hybridisation & endoreduplication (we need this to get 2 copies of each)
A and B sets often partially homologous - homeologous e.g. bread wheat AA BB DD
What is one rule of polyploidy that is generally followed?
Species rarely have odd numbers of x number (monoploid number) e.g. 3x
Why is accurate segregation in meiosis important for polyploidy?
Accurate segregation at the first meiotic division req chromosome pairing & so req a PAIRING PARTENER
How efficient is meiosis in diploids & tetraploids?
Meiosis yields viable gametes
How efficient is meiosis in triploids?
Very, very inefficient due to random segregation of unpaired homologue
What advantages over diploid relatives can polyploidy cause?
- Inc cell size = larger fruits, flowers & organism
- Advantageous characteristics from multiple species (allopolyploids) (immediate hybrid vigour)
- Whole genome duplications allow long term evolution of genetic novelty
What are the possible disadvatages of polyploidy?
Sterility (problems forming “balanced” gametes during meiosis), especially for odd-numbered polyploids
What can even numbered allopolyploids produce?
Can produce balanced gametes at high freq & exist as fully fertile polyploid specie propagated by seed
(i.e. all the chromosmes can pair up as bivalents & segregation in orderly)
What happens if we have 3x pairing?
Makes a pairing between 2 homologous chromosomes but leaves an extra chromsomes that doesn’t pair
Third extra one segregates randomly
What happens with a triploid organism who’s karyotype should be x=2?
3 copies of chromosmes –> 2 accurately segregate; but 3rd segregates randomly
Makes aneuploid gametes
Got to have same no. chromosomes to be viable
What is an aneuploid gamete?
A gamete with an abnormal amount of chromosomes
Why do gametes have to have the same number of chromosomes to be viable?
Zygote has different no. copies of chromsomes
Proteins produced will not be balanced = devleopmental issues
Zygote will not be viable
Why is triploidy in chromsome 22 not equivalent 23?
22 has many more genes than 23 (even tho 23 is larger it is gene sparse)
Therefore 23 isn’t affected too much when there is an extra chromsome present however 22 being gene dense this will have signifiacnt effect (same for 15)
= embryo inviable as it’s triploid
