HMB265H1 Lecture Notes - Lecture 21: Polyploid, Aneuploidy, Monosomy

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HMB265 Lecture 17 Changes in Chromosome number
Euploidy complete sets of chromosomes
- Diploid 2n (normal chromosome complement)
- Monoploidy only one set of chromosomes
- Polyploidy more than the number of sets of chromosomes
o Triploid 3n
o Tetraploid 4n
Aneuploidy loos or gain of one or more chromosomes
- Monosomy missing one chromosome (2n -1)
- Trisomy extra chromosome (2n + 1)
- Tetrasomy four chromosomes (2n + 2)
Monoploidy
- Male bees, wasps and ants
- Parthenogenesis development of an unfertilized egg into an embryo without
fertilization
o Singe set of chromosomes
o Produce gametes by mitosis
- Usually lethal in other systems
o Unmasks recessive lethal
o If individual survives to adulthood no meiosis, sterility
- Monoploidy can be produced experimentally
o E.g. to create monoploid plant
o Monoploid plants have many uses including:
Visualize recessive traits directly
Introduction of mutations
Polyploidy
- Very common in plants
o Associated with origin of new species
o Associated with larger size and plant
o E.g. alfalfa, coffee, peanuts are tetraploid
o E.g. large strawberries are octoploid
- Autopolyploid
o Originate within a species
o E.g. autotriploid (2n +n = 3n)
Tetraploid parents and diploid parent have a sterile triploid zygote
This suggests that there is reproductive isolation between the two parents
hence they are two different species
Autotriploids are sterile due to formation of aneuploid gametes
E.g. bananas and watermelons
- Autotetraploids
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