Lecture 52. Chromosomal (Segmental) Variation Flashcards
What are chromosomal mutations?
Change in the chromosome number per cell
Large-scale (segmental) change in chromosome structure
Visible by microscopy
Why investigate chromosomal mutations?
Cytological insight into meiosis
Medical insight in causes of genetic disease
Molecular insight of how genes interact throughout a genome
Evolutionary insight (e.g., origin of new species)
What does n mean in terms of chromosomes?
Number of chromosome sets
What does 1n represent?
Monoploid
What does 2n represent?
Diploid
What does 3n represent?
Triploid
What does 4n represent?
Tetraploid
What does aneuploid mean?
Change in number of some but not all chromosomes
Is monoploidy useful in most animal species?
No, it is non-viable in most animal species
In what animals is monoploidy useful?
Social insects (ants, bees and wasps)
Males are monoploid & develop by parthenogenesis (gametes from mitosis)
Why is monoploidy useful in plant breeding?
Pollen grains subjected to cold shock begin to divide
What is an example of a triploid plant?
Banana
What are examples of tetraploid plants?
Coffee, cotton, peanut, potato, oilseed rape
What are examples of hexaploid plants?
Oat and wheat
What is an example of an octaploid plant?
Strawberry
What does paleotetraploid mean?
Looks like and is functionally a diploid, but used to be a tetraploid
What are examples of paleotetraploid plants?
Cabbage and soybean
What are examples of tetraploid animals?
African clawed frog, viscacha rat, rainbow trout
What is a common cause for the origin of new plant species?
Polyploidy
What increases with higher ploidy?
Size of organism
What are the two origins of polyploidy?
Autopolyploidy and allopolyploidy
What does autopolyploidy mean?
Derived from the same diploid species
What does allopolyploidy mean?
Derived from different progenitor species
How was hexaploid wheat derived?
Derived from three ancestral diploid species (each n=7)
What are the genomes in hexaploid wheat referred to as?
A, B & D
What can be used to disrupt spindle assembly and thereby block chromosomal segregation?
Colchicine
What are the consequences of meiosis in a triploid?
Highly sterile gametes
What can meiosis in an autotetraploid result in?
Two bivalents (normal)
One quadrivalent (normal)
Univalent + Trivalent (abnormal)
What occurs after meiosis malfunctions?
Non-disjunction
What are the consequences of non-disjunction in meiosis I?
Trisomic and monosomic daughter cells (both lethal)
What are the consequences of non-disjunction in meiosis II?
Disomic daughter cells (normal)
What are the consequences of miss-aligned repeat sequences?
Unequal crossing-over & gain or loss of repeats
What is a pericentric inversion?
A large segmental inversion that encompasses the centromere
What is a paracentric inversion?
A large segmental inversion that does not encompass the centromere
What happens if there is no recombination within an inversion loop?
No deletion or duplication is possible
What happens if a crossover within an inversion loop takes place?
Dicentric and acentric chromosomes will be created
What occurs in heterozygous translocation?
One pair of chromosomes is interchanged whilst the other pair remains normal
What occurs in homozygous translocation?
Both pairs of chromosomes are interchanged
How can cancer be caused by somatic translocation?
ABL encodes a protein kinase that transduces a signal for cell proliferation, which is initiated by growth factor
Chimeric protein is always active (cancerous)
