Final Exam (3) Flashcards
What are chromosomal variations? Are they genetic?
- permanent changes in chromosomes
- passed on to offspring if they effect germline (cells that will become gametes)
What are the 2 general types of chromosomal variation?
- chromosome rearrangement: changes in the structure of individual chromosomes
- changes in the number of chromosomes: 1+ chromosomes added or deleted
What are the four types of chromosomal rearrangements?
- deletion
- duplication
- inversion
- translocation
What is chromosomal deletion?
- the loss of a segment, internal or terminal, of a chromosome
How does chromosomal deletion occur?
- arise by terminal ends breaking off (one break) or internal breaking and rejoining of incorrect ends (2 breaks)
OR unequal crossing over
What determines the severity of impacts of chromosomal deletion?
what is lost and how big it is
How are deletions detected?
- deletion loops can be detected during meiosis
- a variety of molecular methods can also detect decrease heterozygosity and gene dosage
What are some consequences of chromosomal deletion?
- consequences depend on what/what size is lost
- los of DNA sequences
- Acentric chromosome: deletions which span a centromere, eccentric chromosome generally removed during cell division, may be lethal
- pseudodominance: an allele that is normally recessive is expressed
- haploinsufficiency: deletions may impact gene dosage where some genes require 2 copies of a protein to be expressed properly
What is Cri-du-chat syndrome?
top half of one pair of chromosome 5 is lost - leads to genetic disorders
Describe duplications. are they harmful?
- repetition of a chromosome segment
- tandem duplication is the most common (2 repeated)
- single gene or cluster of genes may be duplicated
- nothing lost so often has little consequences, offspring normally viable
- however because excess or unbalanced gene dosage can cause some problems in some cases
Why are duplications important for evolution?
- duplication provides raw material for new genes/adaptations
- 5% of human genome is duplications
What are the origins of duplications?
- duplications primarily derived from unequal crossing over of misaligned chromosomes during meiosis
- also can occur in deletions
How are duplications detected?
- duplicated strand forms a loop
- various molecular methods detect higher gene dosage
What are the evolutionary consequences of duplication?
a) both are functional = redundancy = can impact gene dosage and cause problems
b) one gene is deactivated = pseudo gene (human genome is littered with pseudogenes: one bad gene can ‘break’ the gene)
c) neofunctionalization: one takes on a new property
Describe an example of neofunctionalization
- in hemoglobin : 2 instances of duplication result in alpha and beta gene clusters which form hemoglobin protein!
- Neo functionalization creates new gene families and is the source of new genes
- what are some consequences of duplication? provide an example
- gene dosage can impact phenotype
- amount of protein is sometimes directly proportional to the number of genes present, so duplication can lead to over expression of protein
example: bar bodies in flies
- duplication results in fewer eye facets
-sometimes the only difference in phenotypes is gene dosage
Describe salivary amylase as it pertains to gene dosage
- humans have 5-8 salivary amylase thanks to duplication
- dogs most similar
What are inversions?
- breaks on a chromosome followed by reinsertion in the opposite orientation
- paricentric: invasion occurs around the centromere
- paracentric: inversion occurs beside the centromere
What are the impacts of inversions?
- often none
- sometimes there is an effect since genes are moving
what are the consequences of inversion by position
- positions effects
- change in location can alter function
- genes in/near chromatin may not be expressed
eg; red eye drosophila
what are the consequences of inversion for recombination an production of gametes?
- suppression of recombination!!
- if no crossing over occurs gametes are typically viable because the genetic nor is not lost or gained
- if crossing over occurs …
outside of inverted region .. viable
within inverted region .. some no viable and reduced recombination frequency
Describe crossing over within a paracentric inversion
- the resulting recombinant gametes are non-viable since they’re missing some genes
Describe crossing over within pericentric inversion?
- resulting recombinant gametes are non viable since genes are missing or present in too many copies
Describe translocation
- exchange of segments between two homologous chromosomes or a different region on the same chromosome
- can be reciprocal or non-reciprocal
- if no genetic material is lost considered balanced translocation
what is a balanced translocation?
- no genetic material is lost
What are the consequences of reciprocal translocation
- changes position of genes
- can alter expression due to interaction with other proteins or production of a new fusion protein
Describe the phliadelphia chromosome
chromsome 9 and chromosome 22 combine ends to produce BCR-ABL gene which codes for a fusion protein that functions improperly: Causes CML a rare disease that affects types of WBC
why is inversion’s ability to repress recombination interesitng?
- consequences for adaption/evolution
- lack of recombination means that genes within the inverted region are free to diverge and produce different adaptations
Describe the ruff inversion
- european wading sandpiper
- 3 types: indépendant, satellite, faeder
- faeder/satellite : 3.8 mya an 4.5 Mb inversion occurred
- faeders came first, then a rare crossover event restored some of the independent into the faeder, producing satellite - a mix between the two
-inversion is lethal in the homozygous conditions but the reproductive success outweighs the risks of getting homozygous (similar to sickle cell anemia in humans)
What does it mean for the sandpipers that genes with alternate orientations of invention can diverge dramatically
- alternate orientations can diverge dramatically even if there is no divergence elsewhere
- inside inversion between independent and satellites ~1/4%
- outside inversion site ~0%
- still caused divergence and produced different set of adaptations!
How do chromosomal rearrangements impact cod behaviour and temperature adaptations?
