Bentzen 11 - Chromosome Variations II Flashcards
What is aneuploidy?
An increase or decrease in the number of individual chromosomes (eg. trisomy)
What is polyploidy?
The increase in the number of sets of chromosomes (ef. every copy of every chromosome being triploid)
What are the four most common types of aneuploidy in diploid (2n) individuals?
Nullisomy (loss of both members of a pair of homologous chromosomes)
Monosomy (Loss of a single chromosome)
Trisomy (Gain of a single chromosome)
Tetrasomy (gain of two homologous chromosome)
What is double monosomic aneuploidy?
Loss of 2 non-homologous chromosomes (rare)
What is double trisomic aneuplody?
Gain of two non-homologous chromosomes (rare)
What are two origins of aneuploidy?
- Nondisjunction in meiosis or mitosis
2. Deletion of a centromere leads to chromosome loss
What is the gamete outcome in trisomy?
May be viable
What is the gamete outcome in monosomy?
Usually not viable, except for sex chromosomes
What is the most common cause for human spontaneous abortion?
Aneuploidy
What causes trisomy 21 (Downs Syndrom)?
Nondisjunction in the first meiotic division. 75% of the time the nondisjunction occurs in the mom
Why is it that trisomy occurences increase with increasing maternal age?
Possibly due to fact that oocytes are fomed by birth, in arrested stage of meiosis
What is familial down syndrome?
When an extra copy of chromosome 21 is attached to another chromosome (form parent who underwhent Robertsonian translocation and subsequently has 45 chromosomes- but normal phenotype)
Where is polyploidy common?
In plants
What is autopolyploid?
Multiples of the same genome (eg. autotetraploid - 4n)
What is allopolyploid?
Multiples of closely related genome (eg. allotetraploid - 4n; 2n from species I and 2n from species II)
What can produce autotetraploid?
Nondisjunction of all chromosomes during MITOSIS
What can cause autopolyploidy?
Nondisjunction of all chromosomes during meiosis. (eg. diploid gamete plus normal gamete equals autotriploid (3n))
Why are people with autopolyploidy normally sterile?
Most gametes produced are genetically ubalanced
How can sterile hybrid organisms be converted into fertile ‘new’ species?
Chromosome doubling by mitotic nondisjunction
How can you generate allopolyploids?
By adding two 2n amphidiploids together you can make a allotetraploid cross between the two organisms. If the allotetraploid organisms is viable than this is a cross which makes a new species (like a cabbish)
What is cell volume correlated with? Which is in turn correlated with?
Cell volume correlated with nucleus volume and nucelus volume correlated with genome size. This is why polyplois often have bigger leaves, fruits and seeds
