polyploidy Flashcards
monoploidy
only one set of chromosomes (N)
polyploidy
more than the normal number of sets of chromosomes
tetraploid = 4N
triploid = 3N
true or false triploids are not fertile?
true
Autopolyploids
- usually have double chromosomes
- chromosome sets are all identical (identical homologous groups)
- all chromosomes are derived from the same species
- have more vegetative growth and less seed production (especially 3N)
autopolyploidy through mitosis
- goes through steps correctly except during cytokinesis there is no cell division
- same species doubled its own genetic material
- if happened in animal, cell dies
autopolyploidy in meiosis
- in meiosis I cell doesn’t separate due to non-disjunction
- produces a 2n gamete to enter meiosis II
- meiosis II happens normally and in fertilization 2n gamete fuses with n gamete to produce an autotriploid (3n)
why is polyploidy more common in plants
it is easier for them to reproduce asexually
sterile
not able to reproduce
why are many polyploids sterile
due to problems with pairing and separation of homologous chromosomes in meiosis
Polyploidy example: 3N = 33 bananas
meiosis I creates 11 bivalents and 11 univalents
- in anaphase I, one chromosomes is excluded and ends up on one side which causes uneven gametes
OTHER POSSIBILITY
meiosis I creates 11 trivalents
- all homologous chromosomes stick together and end up on same side
triploid cell in meiosis: pairing of 2 or 3 homologs
1) in meiosis I, two homologous chromosomes pair whereas the other segregates randomly OR all three pair and segregate randomly
2) in meiosis II, some of the resulting gametes have 2 chromosomes and some have 1
triploid cell in meiosis: no pairing of homologs
1) in meiosis I, none of the chromosomes pair and all three move to the same cell after anaphase I
2) in meiosis II, some gametes have 3 chromosomes and some have none
True or false - if the homologous chromosomes aren’t separated in meiosis I they will be separated in meiosis II
False - meiosis II will always separate sister chromatids even if homologous chromosomes were not separated in meiosis I
viable gametes
segregation decisions go the same way by all cells
allopolyploids
result from crosses between 2 or more species
- gametes have to be able to fertilize each other meaning reproductive system of species must be similar enough
breeding allopolyploids example: plants
1) gametes from two diploid plants unite to form a hybrid
2) the hybrid is sterile because meiosis is highly irregular
3) the chromosomes are doubled creating a tetraploid (allotertaploid)
4) meiosis in the tetraploid is regular because there are homologous pairs
5) the euploid gametes produced by the tetraploid can combine to propagate the organism sexually
why can’t sterile hybrids produce gametes
- meiosis doesn’t work
- chromosomes A and B aren’t homologous
- however mitosis can still work
chromosome doubling in sterile hybrids
- makes a sterile hybrid able to reproduce
- meiosis I can now happen on the A’s and B’s seperatly
true or false - plants that can reproduce asexually are still viable if A and B are no compatible
ture
when is 2N not a true diploid
when chromosomes are doubled in hybrids and the now 4N species makes 2N gametes
- not true diploid because you don’t have pairs
allohexaploidy example: bread
species 1: 2N =14
species 2: 2N = 14
both have N7 gametes and produce a 2N = 14 sterile offspring
- gametes are not homologous so no meiosis can happen
true or false : when a species is labeled 2N means they have 2 homologous sets
false - implies 2 sets of chromosomes but not that they are necessarily homologous
what happens when a 2N species is crossed with a 4N species
produces a 3N sterile species
- the gametes it produces will not be viable
- if the offsprings chromosomes double it will be a 6N species
- 6N = 6 sets of chromosomes, but 3 sets of diploids
interspecies cross in animals: the mule
donkey 2N = 62 produces N = 31 gametes
horse 2N = 64 produces N = 32 gametes
mule is 2N = 63 sterile
- since it is sterile, not a diploid
bivalent
pair of physically associated chromosomes that have undergone duplication to form a group of 4 chromatids present in metaphase I
