10.2 Variations in Chromosome Number Flashcards
Aneuploidy
Increase or decrease in the number of individual chromosomes
Polyploidy
Increase in the number of sets of chromosomes
Aneuploidy variations (4)
Double monosomic: (2n-2 non-homologous)
Double trisomic: (2n+2 non-homologous)
Nullisomy: (2n-2 homologous)
Tetrasomy: (2n+2 homologous)
Origins of aneuploidy
Non-disjunction in meiosis or mitosis.
Deletion of a centromere leads to chromosome loss.
Trisomy 13
Patau syndrome; 1 in 16000 newborns.
Trisomy 18
Edward’s syndrome; 1 in 5000 live-born infants
Trisomy 21
Down syndrome; 1 in 800 newborns
Primary down syndrome
3 copies of chromosome 21 (47 chromosomes), accounts for most cases and arises from nondisjunction during meiosis division.
Mother contributes extra chromosome in 75% of cases.
Familial down syndrome
An extra copy of chromosome 21 is attached t another chromosome (3-4% of cases).
Arise in offspring whose parents carry a chromosome that underwent Robertsonian translocation (45 chromosomes).
Live births usually have trisomy of _________ (smaller/larger) chromosomes.
Smaller length, larger chromosome number.
Plants tolerate aneuploidy better
Usually viable with reduced fertility, have many variations in phenotype.
Eg., Jimson weed seeds.
Autopolyploidy
Multiples of the same genome. Can occur during mitosis or meiosis and usually results in sterile individuals due to genetically imbalanced gametes.
Allopolyploidy
Multiples of closely related genomes. Creates hybrids whose chromosomes must be doubled to produce fertile gametes.
Polyploids in agriculture
Cell volume is correlated with nucleus volume - bigger leaves, fruits, seeds.
Polyploidy also allows for the production of seedless fruits.
Polyploid bananas
Most domestic bananas are spontaneous hybrids found in the wild, easily wiped out by disease as none have resistance.
