chromosomal mutations - lecture 10 Flashcards
What types of chromosome rearrangements are there?
- duplication
- deletion
- inversion
- translocation
Which is the more common duplication , intra -chromosomal vs inter - chromosomal duplications?
intra chromosomal
What is a Tandem duplication?
Duplicated region is immediately adjacent to the original segment
what is a displaced duplication?
Duplicated segment some distance from the original segment
What is a reverse duplication?
When the duplicate is inverted
What happens to an individual heterozygous for duplication?
Has one normal chromosome and one abnormal one .
What happens to the added gene in an individual heterozygous?
The duplicated chromosome loops out during pairing in prophase 1.
What is one problem with chromosomal deletions?
- Heterozygous conditions may produce imbalanced gene products
What is the second problem with chromosomal deletions?
- Some genes must be present in two copies for normal function
What happens in an paracentric inversion?
centromere unaffected
What happens in an pericentric inversion?
centromere affected
What happens to chromosomes when a heterozygote has one normal chromosome and one chromosome with a deletion?
In prophase 1 , the normal chromosome must loop out for the homologous sequences of the chromosome to align
The mechanism of a paracentric chromosome mutation
- one wild type chromosome and one with a paracentric inversion
- In prophase 1 an inversion loops form , resulting in a chromosome that lacks a centromere
- This part is lost
What are the resulting games from paracentric meiosis?
- 1 normal gamete
- 2 nonviable recombinant gametes
- 1 non- recombinant gamut with a paracentric inversion
What is the mechanism for pericentric meiosis?
Crossing over occurs and produces chromatids which have too many copies of one gene , and not enough of others
Results of pericentric meiosis
- 1 normal recombinant gamete
- 2 non viable recombinant gametes
- 1 non recombinant gamete with pericentric inversion
What is translocation?
movement of genetic material between non -homologous chromosomes
What is a non. - reciprocal translocation?
Genetic material not transferred between both chromosomes ( less common)
What is a Robertsonian Translocation?
A Robertsonian translocation is when the long arms of two chromosomes with centromeres towards the ends (= acrocentric) become joined to a common centromere generating one big chromosome with a centromere near the middle (=metacentric)
nullisomy
Loss of homologous par (2n-2)
monosomy
loss of a single chromosome (2n-1)
trisomy
gain of a single chromosome(2n +1)
tetrasomy
gain of homologous pair (2n +2)
How can aneuploidy arise?
- if a centromere is deleted - spindle fibres cannot attach. no division.
- Robertsonian translation
- non - disjunction
How would reduced cohesion lead to improper segregation?
if sister chromatids not attached properly in prophase , no crossover , crossover needed for proper segregation
How many Down syndrome people have trisomy 21
95% of all Down syndrome patients have trisomy 21. 91% of these are random nondisjunction in egg rather than sperm.
What are the percentage of people who owe Down syndrome to Robertsonian translocation?
4%
The incidence of Aneuploidy and maternal age
increases drastically with maternal age
Is polyploidy more common in animals or plants?
more common plants
What does autoplolyploidy mean?
Accidents of meiosis/ mitosis that produce extra sets of chromosomes, all derived from a single species
What does allopolyploidy?
arises from hybridisation between two species, resulting polyploid carries chromosomes from two or more species
Which is more common? tandem or displaced duplication?
Tandem duplication more common
What is an example of chromosomal deletion?
reduced eye size
What percentage of the human genome is duplicated?
4%
Why do gene inversions affect fitness?
- gene split in middle
- position effects
- disrupted meiosis
What are the Robertsonian translocations fitness effects?
- cuts within genes
- position effects
- loss of genes , due to the small fragment
